
[Federal Register: October 15, 2008 (Volume 73, Number 200)]
[Rules and Regulations]               
[Page 61255-61289]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr15oc08-29]                         


[[Page 61255]]

-----------------------------------------------------------------------

Part III





Environmental Protection Agency





-----------------------------------------------------------------------



40 CFR Part 197



Public Health and Environmental Radiation Protection Standards for 
Yucca Mountain, Nevada; Final Rule


[[Page 61256]]


-----------------------------------------------------------------------

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 197

[EPA-HQ-OAR-2005-0083; FRL-8724-9]
RIN 2060-AN15

 
Public Health and Environmental Radiation Protection Standards 
for Yucca Mountain, Nevada

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: We, the Environmental Protection Agency (EPA), are 
promulgating amendments to our public health and safety standards for 
radioactive material stored or disposed of in the potential repository 
at Yucca Mountain, Nevada. Congress directed us to develop these 
standards and required us to contract with the National Academy of 
Sciences (NAS) to conduct a study to provide findings and 
recommendations on reasonable standards for protection of the public 
health and safety. The health and safety standards promulgated by EPA 
are to be ``based upon and consistent with'' the findings and 
recommendations of NAS. Originally, these standards were promulgated on 
June 13, 2001 (66 FR 32074) (the 2001 standards).
    On July 9, 2004, the U.S. Court of Appeals for the District of 
Columbia Circuit vacated portions of the 2001 standards concerning the 
period of time for which compliance must be demonstrated. The Court 
ruled that the compliance period of 10,000 years was not ``based upon 
and consistent with'' the findings and recommendations of the NAS and 
remanded those portions of the standards to EPA for revision. These 
remanded provisions are the subject of this action.
    This final rule incorporates compliance criteria applicable at 
different times for protection of individuals and in circumstances 
involving human intrusion into the repository. Compliance will be 
judged against a standard of 150 microsieverts per year ([mu]Sv/yr) (15 
millirem per year (mrem/yr)) committed effective dose equivalent (CEDE) 
at times up to 10,000 years after disposal and against a standard of 1 
millisievert per year (mSv/yr) (100 mrem/yr) CEDE at times after 10,000 
years and up to 1 million years after disposal. This final rule also 
includes several supporting provisions affecting the projections of 
expected disposal system performance prepared by the Department of 
Energy (DOE).

DATES: Effective Date: This final rule is effective on November 14, 
2008.

ADDRESSES: EPA has established a docket for this action under Docket ID 
No. EPA-HQ-OAR-2005-0083. All documents in the docket are listed on the 
http://www.regulations.gov Web site. Although listed in the index, some 
information is not publicly available, e.g., Confidential Business 
Information (CBI) or other information whose disclosure is restricted 
by statute. Certain other material, such as copyrighted material, is 
not placed on the Internet and will be publicly available only in hard 
copy form. Publicly available docket materials are available either 
electronically through http://www.regulations.gov, for purchase or 
access from sources identified in the docket (Docket Nos. EPA-HQ-OAR-
2005-0083-0086 and EPA-HQ-OAR-2005-0083-0087), or in hard copy at the 
Air and Radiation Docket, EPA/DC, EPA Headquarters West Building, Room 
3334, 1301 Constitution Ave., NW., Washington, DC. The Public Reading 
Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, 
excluding legal holidays. The telephone number for the Air and 
Radiation Docket is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: Ray Clark, Office of Radiation and 
Indoor Air, Radiation Protection Division (6608J), U.S. Environmental 
Protection Agency, 1200 Pennsylvania Ave., NW., Washington, DC 20460-
0001; telephone number: 202-343-9360; fax number: 202-343-2305; e-mail 
address: clark.ray@epa.gov.

SUPPLEMENTARY INFORMATION: 

I. General Information

A. Does This Action Apply to Me?

    DOE is the only entity regulated by these standards. Our standards 
affect NRC only to the extent that, under Section 801(b) of the EnPA, 
42 U.S.C. 10141 n., NRC must modify its licensing requirements, as 
necessary, to make them consistent with our final standards. Before it 
may construct the repository or accept waste at the Yucca Mountain site 
and eventually close the repository, DOE must obtain authorization for 
these activities from NRC. DOE will be subject to NRC's modified 
regulations, which NRC will implement through its licensing 
proceedings.

B. How Can I View Items in the Docket?

    1. Information Files. EPA is working with the Lied Library at the 
University of Nevada-Las Vegas (http://www.library.unlv.edu/about/
hours.html) and the Amargosa Valley, Nevada public library (http://
www.amargosalibrary.com) to provide information files on this 
rulemaking. These files are not legal dockets; however, every effort 
will be made to put the same material in them as in the official public 
docket in Washington, DC. The Lied Library information file is at the 
Research and Information Desk, Government Publications Section (702-
895-2200). Hours vary based upon the academic calendar, so we suggest 
that you call ahead to be certain that the library will be open at the 
time you wish to visit. The other information file is in the Public 
Library at 829 East Farm Road in Amargosa Valley, Nevada (phone 775-
372-5340). As of the date of publication, the hours are Monday and 
Thursday (9 a.m.-7 p.m.); Tuesday, Wednesday, and Friday (9 a.m.-5 
p.m.); and Saturday (9 a.m.-1 p.m.). The library is closed on Sunday. 
These hours can change, so we suggest that you call ahead to be certain 
when the library will be open.
    2. Electronic Access. An electronic version of the public docket is 
available through the Federal Docket Management System at http://
www.regulations.gov. You may use http://www.regulations.gov to view 
comments, access the index listing of the contents of the official 
public docket, and to access those documents in the public docket that 
are available electronically. To access the docket go directly to 
http://www.regulations.gov and select ``Advanced Docket Search'' under 
``More Search Options.'' In the Docket ID window, type in the docket 
identification number EPA-HQ-OAR-2005-0083 and click on ``Submit.'' 
Please be patient since the search could take several minutes. This 
will bring you to the ``Docket Search Results'' page. From there, you 
may access the docket contents (e.g., EPA-HQ-OAR-2005-0083-0002) by 
clicking on the icon in the ``Views'' column.

C. Can I Access Information by Telephone or Via the Internet?

    Yes. You may call our toll-free information line (800-331-9477) 24 
hours per day. By calling this number, you may listen to a brief update 
describing our rulemaking activities for Yucca Mountain, leave a 
message requesting that we add your name and address to the Yucca 
Mountain mailing list, or request that an EPA staff person return your 
call. In addition, we have established an electronic listserv through 
which you can receive electronic updates of activities related to this 
rulemaking. To subscribe to the listserv, go to https://lists.epa.gov/
read/

[[Page 61257]]

all_forums. In the alphabetical list, locate ``yucca-updates'' and 
select ``subscribe'' at the far right of the screen. You will be asked 
to provide your e-mail address and choose a password. You also can find 
information and documents relevant to this rulemaking on the World Wide 
Web at http://www.epa.gov/radiation/yucca. The proposed rule for 
today's final rule appeared in the Federal Register on August 22, 2005 
(70 FR 49014). We also recommend that you examine the preamble and 
regulatory language for the earlier proposed and final rules, which 
appeared in the Federal Register on August 27, 1999 (64 FR 46976) and 
June 13, 2001 (66 FR 32074), respectively.

D. What Documents are Referenced in This Final Rule?

    We refer to a number of documents that provide supporting 
information for our Yucca Mountain standards. All documents relied upon 
by EPA in regulatory decision-making may be found in our docket (EPA-
HQ-OAR-2005-0083). Other documents, e.g., statutes, regulations, and 
proposed rules, are readily available from public sources. The 
documents below are referenced most frequently in today's final rule.
    Item No. (EPA-HQ-OAR-2005-0083-xxxx).
    0076 Technical Bases for Yucca Mountain Standards (the NAS Report), 
National Research Council, National Academy Press, 1995.
    0086 DOE Final Environmental Impact Statement, DOE/EIS-0250, 
February 2002.
    0383 ``Geological Disposal of Radioactive Waste,'' International 
Atomic Energy Agency Final Safety Requirements (WS-R-4), 2006.
    0417 ``Radiation Protection Recommendations as Applied to the 
Disposal of Long-Lived Solid Radioactive Waste,'' International 
Commission on Radiological Protection Publication 81, 2000.
    0408 ``Regulating the Long-Term Safety of Geological Disposal: 
Towards a Common Understanding of the Main Objectives and Bases of 
Safety Criteria,'' OECD Nuclear Energy Agency, NEA-6182, 2007.
    0421 ``1990 Recommendations of the International Commission on 
Radiological Protection,'' ICRP Publication 60.
    0423 ``2007 Recommendations of the International Commission on 
Radiological Protection,'' ICRP Publication 103.
    0431 Response to Comments Document for Final Rule, EPA-402-R-08-
008, June 2007.

Acronyms and Abbreviations

    We use many acronyms and abbreviations in this document. These 
include:

BID--background information document
CED--committed effective dose
CEDE--committed effective dose equivalent
CFR--Code of Federal Regulations
DOE--U.S. Department of Energy
EIS--Environmental Impact Statement
EnPA--Energy Policy Act of 1992
EPA--U.S. Environmental Protection Agency
FEIS--Final Environmental Impact Statement
FEPs--features, events, and processes
FR--Federal Register
GCD--greater confinement disposal
HLW--high-level radioactive waste
IAEA--International Atomic Energy Agency
ICRP--International Commission on Radiological Protection
NAS--National Academy of Sciences
NEA--Nuclear Energy Agency
NEI--Nuclear Energy Institute
NRC--U.S. Nuclear Regulatory Commission
NRDC--Natural Resources Defense Council
NTS--Nevada Test Site
NTTAA--National Technology Transfer and Advancement Act
NWPA--Nuclear Waste Policy Act of 1982, as amended
NWPAA--Nuclear Waste Policy Amendments Act of 1987
OECD--Organization for Economic Cooperation and Development
OMB--Office of Management and Budget
RMEI--reasonably maximally exposed individual
SSI--Swedish Radiation Protection Authority
SNF--spent nuclear fuel
TRU--transuranic
UK--United Kingdom
UMRA--Unfunded Mandates Reform Act of 1995
U.S.C.--United States Code
WIPP LWA--Waste Isolation Pilot Plant Land Withdrawal Act of 1992

Outline of This Action

I. What Is the History of This Action?
    A. Promulgation of 40 CFR Part 197 in 2001
    B. Legal Challenges to 40 CFR Part 197
II. Summary of Proposed Amendments to 40 CFR Part 197 and Public 
Comments
    A. How Did We Propose To Amend Our 2001 Standards?
    B. What Factors Did We Consider in Developing Our Proposal?
    C. In Making Our Decisions, How Did We Incorporate Public 
Comments on the Proposed Rule?
    D. What Public Comments Did We Receive?
III. What Final Amendments Are We Issuing With This Action?
    A. What Dose Standards Will Apply?
    1. What Is the Dose Standard Between 10,000 Years and 1 Million 
Years?
    2. What Is the Dose Standard for 10,000 Years After Disposal?
    3. How Does Our Final Rule Protect Public Health and Safety?
    4. How Did We Consider Uncertainty and Reasonable Expectation?
    5. How Did We Consider Background Radiation in Developing the 
Peak Dose Standard?
    6. How Does Our Rule Protect Future Generations?
    7. What is Geologic Stability and Why Is it Important?
    8. Why Is the Period of Geologic Stability 1 Million Years?
    9. How Will NRC Judge Compliance?
    10. How Will DOE Calculate the Dose?
    B. How Will This Final Rule Affect DOE's Performance 
Assessments?
IV. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From 
Environmental Health & Safety Risks
    H. Executive Order 13211: Actions That Significantly Affect 
Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-income 
Populations
    K. Congressional Review Act

I. What Is the History of This Action?

    Radioactive wastes result from the use of nuclear fuel and other 
radioactive materials. Today, we are revising certain standards 
pertaining to spent nuclear fuel, high-level radioactive waste, and 
other radioactive waste (we refer to these items collectively as 
``radioactive materials'' or ``waste'') that may be stored or disposed 
of in the Yucca Mountain repository. When we discuss storage or 
disposal in this document in reference to Yucca Mountain, we note that, 
while Public Law 107-200 approved the site at Yucca Mountain for the 
development of a repository for the disposal of spent nuclear fuel and 
high-level radioactive waste, no licensing decision has been made 
regarding the acceptability of the proposed Yucca Mountain facility for 
storage or disposal as of the date of this publication. To save space 
and to avoid excessive repetition, we will not describe Yucca Mountain 
as a ``potential'' repository; however, we intend this meaning to 
apply.
    Once nuclear reactions have consumed a certain percentage of the 
uranium or other fissionable material in nuclear reactor fuel, the fuel 
no longer is useful for its intended purpose. It

[[Page 61258]]

then is known as ``spent'' nuclear fuel (SNF). It is possible to 
recover specific radionuclides from SNF through ``reprocessing,'' which 
is a process that dissolves the SNF, thus separating the radionuclides 
from one another. Radionuclides not recovered through reprocessing 
become part of the acidic liquid wastes that the Department of Energy 
(DOE) plans to convert into various types of solid materials. High-
level radioactive waste (HLW) is the highly radioactive liquid or solid 
wastes that result from reprocessing SNF. The SNF that does not undergo 
reprocessing prior to disposal remains inside the fuel assembly and 
becomes the final waste form for disposal in the repository.
    In the United States, SNF and HLW have been produced since the 
1940s, mainly as a result of commercial power production and national 
defense activities. Since the inception of the nuclear age, the proper 
disposal of these wastes has been the responsibility of the Federal 
government. The Nuclear Waste Policy Act of 1982, as amended (NWPA, 42 
U.S.C. Chapter 108) sets forth the framework for the disposal of SNF 
and HLW. In general, DOE is responsible for siting, constructing, and 
operating an underground geologic repository for the disposal of SNF 
and HLW and the Nuclear Regulatory Commission (NRC) is responsible for 
licensing the construction and operation of this repository, including 
permanent closure and decommissioning of the surface facilities. In 
making this licensing decision for the Yucca Mountain repository, NRC 
must utilize radiation protection standards that EPA establishes 
pursuant to section 801(a) of the Energy Policy Act of 1992 (EnPA, Pub. 
L. 102-486).\1\ Thus, today we are promulgating amendments to our 
public health protection standards at 40 CFR part 197 (which, pursuant 
to EnPA section 801(a), apply only to releases of radioactive material 
stored or disposed of at the Yucca Mountain site, rather than generally 
applicable). NRC will amend its regulations to be consistent with these 
standards.
---------------------------------------------------------------------------

    \1\ EnPA, Public Law No. 102-486, 102 Stat. 2776, 42 U.S.C. 
10141 n. (1994).
---------------------------------------------------------------------------

    On June 3, 2008, pursuant to the NWPA, as amended, DOE submitted a 
license application to NRC seeking a license to construct the 
repository. NRC will determine whether DOE has met NRC's requirements, 
including those implementing 40 CFR part 197, and whether to grant or 
deny authorization to construct the repository and a license to receive 
radioactive material at the Yucca Mountain site.
    In 1985, we established generic standards for the management, 
storage, and disposal of SNF, HLW, and transuranic (TRU) radioactive 
waste (see 40 CFR part 191, 50 FR 38066, September 19, 1985), which 
were intended to apply to facilities utilized for the storage or 
disposal of these wastes, including Yucca Mountain. In 1987, the U.S. 
Court of Appeals for the First Circuit remanded the disposal standards 
in 40 CFR part 191 (NRDC v. EPA, 824 F.2d 1258 (1st Cir. 1987)). We 
later amended and reissued those standards to address issues that the 
court raised. Also in 1987, the Nuclear Waste Policy Amendments Act 
(NWPAA, Pub. L. 100-203) amended the NWPA by, among other actions, 
selecting Yucca Mountain, Nevada, as the only potential site that DOE 
should characterize for a geologic repository for SNF and HLW. In 
October 1992, Congress enacted the EnPA and the Waste Isolation Pilot 
Plant Land Withdrawal Act (WIPP LWA, Pub. L. 102-579). These statutes 
changed our obligations concerning radiation standards for the Yucca 
Mountain candidate repository. The WIPP LWA:
    (1) Reinstated the 40 CFR part 191 disposal standards, except those 
portions that were the specific subject of the remand by the First 
Circuit;
    (2) Required us to issue standards to replace the portion of the 
challenged standards remanded by the court; and
    (3) Exempted the Yucca Mountain site from the 40 CFR part 191 
disposal standards.

We issued the amended 40 CFR part 191 disposal standards, which 
addressed the judicial remand, on December 20, 1993 (58 FR 66398).
    The EnPA set forth our responsibilities as they relate to Yucca 
Mountain and directed us to set public health and safety radiation 
standards for Yucca Mountain. Specifically, section 801(a)(1) of the 
EnPA directed us to ``promulgate, by rule, public health and safety 
standards for the protection of the public from releases from 
radioactive materials stored or disposed of in the repository at the 
Yucca Mountain site.'' Section 801(a)(2) directed us to contract with 
the National Academy of Sciences (NAS) to conduct a study to provide us 
with its findings and recommendations on reasonable standards for 
protection of public health and safety from releases from the Yucca 
Mountain disposal system. Moreover, it provided that our standards 
shall be the only such standards applicable to the Yucca Mountain site 
and are to be based upon and consistent with NAS's findings and 
recommendations. On August 1, 1995, NAS released its report, 
``Technical Bases for Yucca Mountain Standards'' (the NAS Report) 
(Docket No. EPA-HQ-OAR-2005-0083-0076).

A. Promulgation of 40 CFR Part 197 in 2001

    Pursuant to the EnPA, we developed standards specifically 
applicable to releases from radioactive material stored or disposed of 
in the Yucca Mountain repository. In doing so, we considered the NAS 
Report, our generic standards in 40 CFR part 191, and other relevant 
information, precedents, and analyses.
    We evaluated 40 CFR part 191 because those standards were developed 
to apply to sites selected for storage and disposal of SNF and HLW. 
Thus, we believed that 40 CFR part 191 already included the major 
components of standards needed for any specific site, such as Yucca 
Mountain. However, we recognized that all the components would not 
necessarily be directly transferable to the situation at Yucca 
Mountain, and that some modification might be necessary. We also 
considered that some components of the generic standards would not be 
carried into site-specific standards, since not all of the conditions 
found among all potential sites are present at Yucca Mountain. See 66 
FR 32076-32078, June 13, 2001 (Docket No. EPA-HQ-OAR-2005-0083-0042), 
for a more detailed discussion of the role of 40 CFR part 191 in 
developing 40 CFR part 197.
    We also considered the findings and recommendations of the NAS in 
developing standards for Yucca Mountain. In some cases, provisions of 
40 CFR part 191 were already consistent with NAS's analysis (e.g., 
level of protection for the individual). In other cases, we used the 
NAS Report to modify or draw out parts of 40 CFR part 191 to apply more 
directly to Yucca Mountain (e.g., the stylized drilling scenario for 
human intrusion). See the NAS Report for a complete description of 
findings and recommendations (Docket No. EPA-HQ-OAR-2005-0083-0076).
    Because our standards are intended to apply specifically to the 
Yucca Mountain disposal system, we tailored our approach to consider 
the characteristics of the site and the local populations. Yucca 
Mountain is in southwestern Nevada approximately 100 miles northwest of 
Las Vegas. The eastern part of the site is on the Nevada Test Site 
(NTS). The northwestern part of the site is on the Nevada Test and 
Training Range (referred to in our proposal as the Nellis Air Force 
Range). The southwestern part of the site is on Bureau of Land 
Management land. The

[[Page 61259]]

area has a desert climate with topography typical of the Basin and 
Range province. Yucca Mountain is made of layers of ashfalls from 
volcanic eruptions that happened more than 10 million years ago. There 
are two major aquifers beneath Yucca Mountain. Regional ground water in 
the vicinity of Yucca Mountain is believed to flow generally in a 
south-southeasterly direction. For more detailed descriptions of Yucca 
Mountain's geologic and hydrologic characteristics, and the disposal 
system, please see Chapter 7 of the 2001 Background Information 
Document (BID) (Docket No. EPA-HQ-OAR-2005-0083-0050) and the preamble 
to the proposed rule (64 FR 46979-46980, August 27, 1999, Docket No. 
EPA-HQ-OAR-2005-0083-0041).
    We proposed the original standards for Yucca Mountain on August 27, 
1999 (64 FR 46976). In response to our proposal, we received more than 
800 public comments and conducted four public hearings. After 
evaluating public comments, we issued final standards (66 FR 32074, 
June 13, 2001). See the Response to Comments document from that 
rulemaking for more discussion of comments (Docket No. EPA-HQ-OAR-2005-
0083-0043).
    The final standards issued in 2001 as 40 CFR part 197 included the 
following:
     A standard to protect the public during management and 
storage operations on the Yucca Mountain site;
     An individual-protection standard to protect the public 
from releases from the undisturbed disposal system;
     A human-intrusion standard to protect the public after 
disposal from releases caused by a drilling penetration into the 
repository;
     A set of standards to protect ground water from 
radionuclide contamination caused by releases from the disposal system;
     The requirement that compliance with the disposal 
standards be shown for 10,000 years;
     The requirement that DOE continue its projections for the 
individual-protection and human-intrusion standards beyond 10,000 years 
to the time of peak (maximum) dose, and place those projections in the 
Environmental Impact Statement (EIS) for Yucca Mountain;
     The concept of the Reasonably Maximally Exposed Individual 
(RMEI), defined as a hypothetical person whose lifestyle is 
representative of the local population living today in the Town of 
Amargosa Valley, as the individual against whom the disposal standards 
should be assessed; and
     The concept of a ``controlled area,'' defined as an area 
immediately surrounding the repository whose geology is considered part 
of the natural barrier component of the overall disposal system, and 
inside of which radioactive releases are not regulated.
    More detail on these aspects of the 2001 final rule may be found at 
66 FR 32074-32134, June 13, 2001, and 70 FR 49019-49020, August 22, 
2005.

B. Legal Challenges to 40 CFR Part 197

    Various aspects of our standards were challenged in lawsuits filed 
with the U.S. Court of Appeals for the District of Columbia Circuit in 
July 2001. These challenges and the Court's subsequent ruling are 
described briefly here, emphasizing the aspects leading to today's 
final rule, and in more detail in the preamble to the proposed rule (70 
FR 49014, August 22, 2005).
    The State of Nevada, the Natural Resources Defense Council (NRDC), 
and several other petitioners challenged various aspects of our final 
standards on the grounds that they were insufficiently protective and 
had not been adequately justified. The focus of this challenge was the 
10,000-year compliance period. Nevada and NRDC claimed that EPA's 
promulgation of numerical standards that applied for 10,000 years after 
disposal violated the EnPA because such standards were not ``based upon 
and consistent with'' the findings and recommendations of the NAS. NAS 
recommended standards that would apply to the time of maximum risk, 
within the limits imposed by the long-term geologic stability of the 
site, and stated that there is ``no scientific basis for limiting the 
time period of the individual-risk standard to 10,000 years or any 
other value.'' (NAS Report p. 55) The Nuclear Energy Institute (NEI) 
challenged the ground-water protection standards as unnecessary to 
protect public health and safety, contrary to recommendations of the 
NAS, and outside our authority under the EnPA.
    The DC Circuit Court's July 9, 2004 decision dismissed NEI's 
challenge, and all of the challenges by Nevada and NRDC, except one. On 
the question of EPA's 10,000-year compliance period, the Court upheld 
the challenge, ruling that EPA's action was not ``based upon and 
consistent with'' the NAS Report, and that EPA had not sufficiently 
justified on policy grounds its decision to apply compliance standards 
only to the first 10,000 years after disposal. Nuclear Energy Institute 
v. Environmental Protection Agency, 373 F.3d 1251 (D.C. Cir. 2004) (NEI 
).
    The Court concluded that ``we vacate 40 CFR part 197 to the extent 
that it incorporates a 10,000-year compliance period * * *.'' (Id. at 
1315) The Court did not address the protectiveness of the 150 [mu]Sv/yr 
(15 mrem/yr) dose standard applied over the 10,000-year compliance 
period, nor was the protectiveness of the 15 mrem/yr standard 
challenged. It ruled only that the compliance period was not consistent 
with or based upon the NAS findings and recommendations and, therefore, 
was contrary to the plain language of the EnPA.
    As the Court noted, NAS stated that it had found ``no scientific 
basis for limiting the time period of the individual-risk standard to 
10,000 years or any other value,'' and that ``compliance assessment is 
feasible * * * on the time scale of the long-term stability of the 
fundamental geologic regime--a time scale that is on the order of 
106 years at Yucca Mountain.'' As a result, and given that 
``at least some potentially important exposures might not occur until 
after several hundred thousand years * * * we recommend that compliance 
assessment be conducted for the time when the greatest risk occurs.'' 
(NAS Report pp. 6-7) Today's action addresses this recommendation and 
the DC Circuit ruling.

II. Summary of Proposed Amendments to 40 CFR Part 197 and Public 
Comments

    The primary goal of our proposal issued in 2005 was to gather 
public comment on the appropriate response to the Court decision and 
NAS recommendation to assess compliance at the time of maximum dose 
(risk). Therefore, our proposed amendments centered on extending the 
compliance period to capture the peak projected dose from the Yucca 
Mountain disposal system ``within the limits imposed by the long-term 
stability of the geologic environment.'' (NAS Report p. 2) Of course, 
establishing a radiological protection standard to apply at the time of 
peak dose is a uniquely challenging task. Only a small number of 
countries have established standards of any kind for the geologic 
disposal of SNF and HLW. Of these, only Switzerland has established a 
quantitative standard applicable for as long as 1 million years, 
although we are aware that other regulatory bodies outside the U.S. are 
contemplating the need to establish some type of regulation addressing 
these extremely long time frames. Comments received in the course of 
this rulemaking have been helpful given the extraordinary technical 
complexity of this task.

[[Page 61260]]

A. How Did We Propose To Amend Our 2001 Standards?

    We considered carefully the language and reasoning of the Court's 
decision in revising our 2001 standards. As originally promulgated in 
2001, 40 CFR part 197 contained four sets of standards against which 
compliance would be assessed. The storage standard applies to exposures 
of the general public during the operational period, when waste is 
received at the Yucca Mountain site, handled in preparation for 
emplacement in the repository, emplaced in the repository, and stored 
in the repository until final closure. The three disposal standards 
apply to releases of radionuclides from the disposal system after final 
closure, and include an individual-protection standard, a human-
intrusion standard, and a set of ground-water protection standards.
    The Court's ruling vacated only one aspect of 40 CFR part 197: The 
10,000-year compliance period applicable to the disposal standards. 
Therefore, the storage standard, which is applicable only for the 
period before disposal, is not affected by the ruling. Further, the 
Court recognized that the ground-water protection standards were issued 
as an expression of EPA's overall ground-water protection policies and 
were not among the standards addressed by the NAS, either in form or 
purpose (``NAS treated the compliance-period and ground-water issues 
quite differently * * * NAS made no `finding' or `recommendation' that 
EPA's regulation could fail to be `based upon and consistent with' '' 
(NEI, 373 F.3d at 1282)). Therefore, we concluded that the Court's 
vacature of the 10,000-year compliance period, which was explicitly 
tied to recommendations concerning the individual-protection standard, 
does not extend to the ground-water provisions. As a result, we did not 
propose to amend the ground-water protection standards. Nothing in 
today's final rule affects those standards.
    We proposed to revise only the individual-protection and human-
intrusion standards, along with certain supporting provisions related 
to the way DOE must consider features, events, and processes (FEPs) in 
its compliance analyses (70 FR 49014, August 22, 2005). In addition, we 
proposed to adopt updated scientific factors for calculating doses to 
show compliance with the storage, individual-protection, and human-
intrusion standards. We requested comments only on those aspects of the 
individual-protection and human-intrusion standards which were to be 
amended. Specifically, we proposed to:
     Extend the compliance period for the individual-protection 
and human-intrusion standards to 1 million years after disposal 
(closure), consistent with NAS estimates regarding the ``long-term 
stability of the geologic environment'';
     Retain the dose standard of 150 [mu]Sv/yr (hereafter, 15 
mrem/yr) committed effective dose equivalent (CEDE) for the first 
10,000 years after disposal, as promulgated in 2001;
     Establish a dose standard of 3.5 mSv/yr (hereafter, 350 
mrem/yr) CEDE for the period between 10,000 years and 1 million years;
     Clarify that the arithmetic mean of the distribution of 
projected results will be compared to the dose standard for the initial 
10,000 years, and specify use of the median of the distribution of 
projected results between 10,000 and 1 million years;
     Retain the probability threshold (1 in 10,000 chance of 
occurring in 10,000 years, or 1 in 100 million chance of occurring per 
year) below which ``very unlikely'' FEPs may be excluded from 
consideration;
     Allow FEPs with a probability of occurring above the 
probability threshold to be excluded if they would not significantly 
affect the results of performance assessments in the initial 10,000 
years;
     Require consideration of seismic and igneous events 
causing direct damage to the engineered barrier system during the 1 
million-year period;
     Require consideration of the effects of increased water 
flow through the repository resulting from climate change, which could 
be represented by constant conditions between 10,000 and 1 million 
years;
     Require consideration of the effects of general corrosion 
of the engineered barriers between 10,000 and 1 million years; and
     Require use of updated scientific factors, based on 
Publications 60 and 72 of the International Commission on Radiation 
Protection (ICRP), to calculate dose for comparison with the storage, 
individual-protection, and human-intrusion standards.

B. What Factors Did We Consider in Developing Our Proposal?

    Of great concern in extending the compliance period to 1 million 
years is the increasing uncertainty associated with numerical 
projections of radionuclide releases from the Yucca Mountain disposal 
system and subsequent exposures incurred by the Reasonably Maximally 
Exposed Individual (RMEI). This uncertainty affects not only the 
projections themselves, but also the interpretation of the results. 
There is general agreement in the international community that dose 
projections over periods as long as 1 million years cannot be viewed in 
the same context or with the same confidence as projections for periods 
as ``short'' as 10,000 years. As a result, the nature of regulatory 
decision-making fundamentally changes when faced with the prospect of 
compliance projections for the next 1 million years. International 
guidance from the International Atomic Energy Agency (IAEA) and Nuclear 
Energy Agency (NEA), as well as geologic disposal programs in other 
countries, recognize this difficulty and accommodate it by viewing 
longer-term projections in a more qualitative manner, to be balanced 
and supplemented by other considerations that would provide confidence 
in the long-term safety of the disposal system. In effect, numerical 
dose projections are given less weight in decision-making at longer 
times.\2\ Such approaches discourage comparison of projections against 
a strict compliance limit.
---------------------------------------------------------------------------

    \2\ For example, the ICRP's most recent recommendations note 
that ``both the individual doses and the size of the exposed 
population become increasingly uncertain as time increases. The 
Commission is of the opinion that in the decision-making process, 
owing to the increasing uncertainties, giving less weight to very 
low doses and to doses received in the distant future could be 
considered.'' (Publication 103, 2007, Docket No. EPA-HQ-OAR-2005-
0083-0423, Paragraph 222)
---------------------------------------------------------------------------

    This uncertainty was the overriding reason for limiting the 
compliance period to 10,000 years in our 2001 rule. We supplemented 
that 10,000-year compliance period by requiring DOE to continue 
projections through the time of peak dose, consistent with the approach 
favored by the international community. However, while we believed this 
approach was consistent with the NAS recommendation to assess 
compliance at the time of maximum dose (risk) and the committee's 
acknowledgment that policy considerations would also play a role in 
determining the compliance period, the Court concluded that it was 
inconsistent with the NAS recommendation. We concluded that the most 
direct way to address the Court's ruling would be to establish a 
numeric compliance standard for the time of peak dose, within the 
period of geologic stability at Yucca Mountain, which NAS judged to be 
``on the order of one million years.'' (NAS Report p. 2)
    In establishing our final standards, we have considered that the 
level of uncertainty increases as the time period covered by DOE's 
performance

[[Page 61261]]

assessment increases.\3\ Therefore, it is reasonable for us to consider 
how the compliance standard itself might also need to change. 
Specifically, we do not believe that extending the 10,000-year 
individual-protection standard of 15 mrem/yr to apply for 1 million 
years adequately accounts for the considerations outlined above or 
represents a reasonable test of the disposal system (more extensive 
discussion of uncertainty in performance assessments is in section 
III.A.4 of this document, ``How Did We Consider Uncertainty and 
Reasonable Expectation?''); see also 66 FR 32098. We turned back to the 
international technical literature for advice regarding appropriate 
points of comparison for doses projected over hundreds of thousands of 
years. A number of sources suggested that natural sources of 
radioactivity would provide an appropriate benchmark for such 
comparisons. In exploring this approach further, we found that the 
variation in background radiation across the United States covered a 
wide range (from roughly 100 mrem/yr to 1 rem/yr), primarily because of 
local variation in radon exposures. We chose for our proposal a level 
of 350 mrem/yr, which is close to a widely-cited estimate of 300 mrem/
yr for the national average background radiation exposure (NAS Report 
Table 2-1), but specifically represented the difference between 
estimated background levels in Amargosa Valley and the State of 
Colorado. This level was proposed for both the individual-protection 
and human-intrusion standards as offering both a reasonable level of 
protection and a sound basis for regulatory decision-making when 
exposures are projected to occur hundreds of thousands of years into 
the future. Selecting such a level would also provide an indication 
that exposures incurred by the RMEI in the far future from the 
combination of natural background radiation and releases from the Yucca 
Mountain disposal system would not exceed exposures incurred by 
residents of other parts of the country today from natural sources 
alone. Today's final rule adopts a more stringent standard that is not 
derived from an analysis of background radiation, as explained in 
sections III.A.1 (``What is the Peak Dose Standard Between 10,000 and 1 
Million Years After Disposal?'') and III.A.5 (``How Did We Consider 
Background Radiation in Developing The Peak Dose Standard?'') of this 
document.
---------------------------------------------------------------------------

    \3\ ``We recognize that there are significant uncertainties in 
the calculations and that these uncertainties increase as the time 
at which peak risk occurs increases.'' (NAS Report p. 56)
---------------------------------------------------------------------------

    Uncertainty in long-term projections also influenced our proposal. 
Given the probabilistic nature of performance assessments, it is 
possible that some combinations of parameter values will result in very 
high doses, even if such combinations have an extremely low probability 
of occurring. Although there may be only a few results that are very 
high, extreme results have the potential to exert a strong influence on 
the arithmetic mean, which could make the mean less representative of 
all performance projections. This possibility may be increased by the 
introduction of additional, and possible excessive, conservatisms as a 
way to account for uncertainties. We expressed a preference for a 
statistical measure that would not be strongly affected by either very 
high- or low-end estimates, believing it appropriate to focus on the 
``central tendency'' of the distribution, where the bulk of the results 
might be expected to be found. We proposed the median of the 
distribution as being most representative of central tendency. Because 
it is always located at the point where half the distribution is higher 
and half lower, the median depends only on the relative nature of the 
distribution, rather than the absolute calculated values. Given our 
concerns about specifying a peak dose compliance value against which 
performance would be judged for a period up to 1 million years, we 
believed the median might also provide a reasonable test of long-term 
performance. Today's final rule departs from the proposal by adopting 
the arithmetic mean as the statistical measure of compliance to be 
applied at all times, as explained in section III.A.9 of this document 
(``How Will NRC Judge Compliance?'').
    Our consideration of FEPs also was affected to some extent by 
uncertainty, as well as by conclusions of the NAS committee. In our 
proposal, the overall probability threshold for inclusion of FEPs 
remained the same as in the 2001 rule, which we believe provides a very 
inclusive initial screen that captures both major and minor factors 
potentially affecting performance. Uncertainty plays a role in the 
sense that very gradual or infrequent processes and events may begin to 
influence performance only at times in the hundreds of thousands of 
years, when the overall uncertainty of assessments is increasing. The 
additional uncertainty introduced by these slow-acting FEPs led us to 
propose the exclusion of FEPs if they were not significant to the 
assessments in the initial 10,000 years. We believed this would still 
provide for robust assessments that would address the factors of most 
importance over the entire 1 million-year period. We did consider in 
our proposal whether significant FEPs might not be captured using this 
approach. In evaluating whether excluded FEPs might become more 
probable or more significant after 10,000 years, and therefore should 
not be eliminated, we identified general corrosion as a FEP that is 
certain to occur and represents a significant failure mechanism at 
longer times, even though it is less significant in the initial 10,000 
years.
    We also consulted the NAS Report for advice on handling long-term 
FEPs. NAS identified three ``modifiers'' that it believed could 
reasonably be included in assessments: seismic events, igneous events, 
and climate change. (NAS Report p. 91) We developed provisions 
addressing these FEPs that incorporated the views expressed by the NAS. 
For seismic and igneous events, we proposed that DOE focus its 
attention on events causing direct damage to the engineered barriers. 
We took this approach because failure of the engineered barrier system, 
particularly the waste packages, is the predominant factor in 
determining the timing and magnitude of the peak dose, and is the 
overriding uncertainty in assessing performance of the disposal system. 
To address climate change, we required DOE to focus on the effects of 
increased water flow through the repository, which is the climatic 
effect with the most influence on release and transport of 
radionuclides. We determined that such a focus would provide the basis 
for a reasonable test of the disposal system, and that climate change 
beyond 10,000 years could be represented by constant conditions 
reflecting precipitation levels that differ from current conditions, 
which eliminates unresolvable speculation regarding the timing, 
magnitude, and duration of climatic cycles over this time frame. We 
also directed that NRC establish the exact nature of future climate 
characteristics to be used in performance assessments. NRC subsequently 
issued a proposal to specify a range of values for deep percolation 
into the repository, which DOE would use as another parameter in its 
probabilistic performance assessments. (70 FR 53313, September 8, 2005)
    Finally, we proposed to update the factors used to calculate dose 
for the storage, individual-protection, and human-intrusion standards. 
Our generic standards in 40 CFR part 191, and by inference our Yucca 
Mountain standards in 2001, specified the factors associated with ICRP 
Publications 26

[[Page 61262]]

and 30 (Docket Nos. EPA-HQ-OAR-2005-0083-0425 and 0428, respectively). 
Since we issued 40 CFR part 191, ICRP has modified the models and 
associated organ-weighting factors to more accurately calculate dose. 
See ICRP Publications 60 and 72 (Docket Nos. EPA-HQ-OAR-2005-0083-0421 
and 0427, respectively). We used this newer method in 1999 to develop 
our Federal Guidance Report 13, ``Cancer Risk Coefficients from 
Exposure to Radionuclides'' (Docket No. EPA-HQ-OAR-2005-0083-0072). 
Where possible, we believe it is appropriate to adopt the latest 
scientific methods.\4\
---------------------------------------------------------------------------

    \4\ ICRP published its most recent recommendations in 
Publication 103, issued in 2007 (Docket No. EPA-HQ-OAR-2005-0083-
0423). EPA has not determined the impact of these recommendations on 
its current dose and risk estimates, but may decide to adopt them in 
the future. Today's final rule will incorporate the ICRP 60 
recommendations as consistent with EPA's current federal guidance; 
however, we have provided some flexibility for use of newer 
dosimetry in the future if deemed appropriate by NRC.
---------------------------------------------------------------------------

C. In Making Our Final Decisions, How Did We Incorporate Public 
Comments on the Proposed Rule?

    Section 801(a)(1) of the EnPA requires us to set public health and 
safety radiation protection standards for Yucca Mountain by rulemaking. 
Pursuant to Section 4 of the Administrative Procedure Act (APA), 
regulatory agencies engaging in informal rulemaking must provide notice 
of a proposed rulemaking, an opportunity for the public to comment on 
the proposed rule, and a general statement of the basis and purpose of 
the final rule.\5\ The notice of proposed rulemaking required by the 
APA must ``disclose in detail the thinking that has animated the form 
of the proposed rule and the data upon which the rule is based.'' 
(Portland Cement Association v. Ruckelshaus, 486 F. 2d 375, 392-94 (DC 
Cir. 1973)) The public thus is enabled to participate in the process by 
making informed comments on the proposal. This provides us with the 
benefit of ``an exchange of views, information, and criticism between 
interested persons and the agency.'' (Id.)
---------------------------------------------------------------------------

    \5\ 5 U.S.C. 553.
---------------------------------------------------------------------------

    There are two primary mechanisms by which we explain the issues 
raised in public comments and our reactions to them. First, we discuss 
broad or major comments in the succeeding sections of this preamble. 
Second, we are publishing a document, accompanying today's action, 
entitled ``Response to Comments'' (Docket No. EPA-HQ-OAR-2005-0083-
0431). The Response to Comments document provides more detailed 
responses to issues addressed in the preamble. It also addresses all 
other significant comments on the proposal. We gave all the comments we 
received, whether written or oral, consideration in developing the 
final rule.

D. What Public Comments Did We Receive?

    The public comment period ended November 21, 2005. We received more 
than 300 individual submittals, although any particular submittal could 
contain many specific comments. We also received many more submissions 
as part of mass comment efforts, in which organizations encourage 
commenters to use prepared texts or comment on specific aspects of the 
proposal. All, or representative, comments are available electronically 
through the Federal Document Management System (FDMS), available at 
http://www.regulations.gov. See the ``General Information'' section of 
this document for instructions on how to access the electronic docket. 
Some submittals may be duplicated in FDMS, as a commenter may have used 
several methods to ensure the comments were received, such as fax, e-
mail, U.S. mail, or directly through FDMS.
    A significant number of comments addressed the proposed peak dose 
standard of 350 mrem/yr, which would apply between 10,000 and 1 million 
years. Most commenters opposed our proposal, arguing that it is much 
higher than any previous standard, is not protective, is not equitable 
to future generations, and is based on inappropriate use of background 
radiation data. Many commenters also took issue with our proposal to 
use the median of the distribution of results as the statistical 
measure between 10,000 and 1 million years, viewing this measure as 
inconsistent with NAS recommendations to use the mean. Commenters also 
viewed the median as too ``lax'' and likely to discount scenarios that 
would result in high exposures. We also received comment on our 
proposal concerning the assessment of FEPs beyond 10,000 years, with 
some comments expressing the opinion that we had inappropriately 
constrained the analyses, leaving out potentially significant FEPs. 
Some commenters disagreed with our general premise that uncertainty 
increases with assessment time and further disagreed that we should 
take uncertainties into account when considering standards applicable 
to the far future. These specific comments, and our responses to them, 
will be discussed in more detail in section III of this document and in 
the Response to Comments document associated with this action (Docket 
No. EPA-HQ-OAR-2005-0083-0431).
    Some commenters also questioned our conclusion that extending the 
compliance period is the appropriate way to respond to the Court 
ruling. These commenters point out that the Court's opinion could be 
interpreted to permit us to justify the approach taken in our 2001 
standards. They cite statements by the Court such as ``[i]t would have 
been one thing had EPA taken the Academy's recommendations into account 
and then tailored a standard that accommodated the agency's policy 
concerns'' and ``[h]ad EPA begun with the Academy's recommendation to 
base the compliance period on peak dosage and then made adjustments to 
accommodate policy considerations not considered by NAS, this might be 
a very different case'' (NEI, 373 F.3d at 1270 and 1273, respectively) 
to support the thesis that the Court's judgment was based primarily on 
the presentation of our case, rather than the substance. In the 
commenters' view, the Court would have been receptive to our arguments 
had they been presented differently, and the Court provided a clear 
``road map'' to justify keeping our original standards in place. In 
addition, these and other commenters viewed extending the compliance 
period to 1 million years as not justifiable either scientifically or 
as a matter of public policy. We believe that the approach we are 
taking is the most appropriate way to address the concerns raised by 
the Court's decision, particularly given the weight accorded by the 
Court to the NAS technical recommendations concerning the period of 
geologic stability. As we stated in our proposal, ``it is not clear how 
EPA's earlier explanation of its policy concerns might be reconciled 
with NAS's technical recommendation.'' (70 FR 49032) Accordingly, 
today's final rule implements the NAS technical recommendation with 
regard to the length of time for the compliance period while still 
accommodating our policy concerns in the provisions related to the peak 
dose standard, and FEPs.
    We received some comments that suggested we should have provided 
more or better opportunities for public participation in our decision 
making process. For example, comments suggested that we should have 
rescheduled public hearings, extended the public comment period, and 
provided alternatives to the public hearing process. We provided 
numerous opportunities and avenues for public participation in the 
development of these standards. For example, we held public hearings in 
Washington, DC; Las

[[Page 61263]]

Vegas, NV; and Amargosa Valley, NV. We also opened a 60-day public 
comment period and met with key stakeholders before and during that 
time. In response to requests from stakeholders, we extended the public 
comment period by 30 days and held an additional public hearing in Las 
Vegas. We conducted targeted outreach to Native American tribal groups 
and have fully considered all comments received through December 31, 
2005, after the end of the extended public comment period. These 
measures are in full compliance with the public participation 
requirements of the Administrative Procedure Act.
    Several commenters supported our role in setting standards for 
Yucca Mountain. Other commenters thought that aspects of our standards 
duplicate NRC's implementation role. We believe the provisions of this 
rule clearly are within our authority and they are central to the 
concept of a public health protection standard. We also believe our 
standards leave NRC the necessary flexibility to adapt to changing 
conditions at Yucca Mountain or to impose additional requirements in 
its implementation efforts, if NRC deems them to be necessary.
    We also received many general comments, and others addressing 
topics that are outside the scope of our authority under the EnPA. For 
example, several commenters simply expressed their support for, or 
opposition to, the Yucca Mountain repository. Other comments suggested 
our standards should explicitly consider radiation exposures from all 
sources because of the site's proximity to the Nevada Test Site (NTS) 
and other sources of potential contamination. Also, a number of 
commenters suggested that we should explore alternative methods of 
waste disposal, such as neutralizing radionuclides. Comments also 
expressed concern regarding risks of transporting radioactive materials 
to Yucca Mountain. These comments all raise considerations that are 
outside the scope of our authority and this rulemaking.
    Many comments touched on issues related to our authority and 
standards, but outside the limited scope of this rulemaking. In 
particular, many comments urged us to extend the ground-water 
protection limits to the time of peak dose within the 1 million-year 
compliance period. Many of these commenters disagreed with our position 
that the ground-water standards were not the subject of the Court's 
ruling, and that in fact the Court left us with discretion regarding 
the content and application of those standards. Others believed that we 
are obligated to accept comments on this topic, since we were proposing 
not to change the standards. We stated clearly in our proposal that we 
were not soliciting, and would not consider, comments on this issue.

III. What Final Amendments Are We Issuing With This Action?

    This section describes the provisions of our final rule, our 
rationale, and our response to public comments on various aspects of 
our proposal. Today's final rule establishes the dose standards 
applicable for a period up to 1 million years after disposal, the 
statistical measures used to determine compliance with those standards, 
the methods to be used to calculate the dose, and the requirements for 
including features, events, and processes (FEPs) in the performance 
assessments.

A. What Dose Standards Will Apply?

    Today's final rule includes an individual-protection standard 
consisting of two parts, which will apply over different time frames. 
The post-10,000-year public health protection standard limits the long-
term peak dose to the RMEI from the Yucca Mountain disposal system to 1 
mSv/yr (100 mrem/yr) committed effective dose equivalent (CEDE). This 
post-10,000-year (also referred to as the ``peak dose'') standard 
addresses and responds to the DC Circuit ruling that our 2001 
standards, with the compliance period limited to 10,000 years, were 
inconsistent with the recommendations of the NAS. The post-10,000-year 
standard was the focus of our proposal and will apply after 10,000 
years through the period of geologic stability, up to 1 million years 
after disposal. The other part of the individual-protection standard, 
which will apply over the initial 10,000 years after disposal, consists 
of the 150 [mu]Sv/yr (15 mrem/yr) CEDE individual-protection standard 
promulgated in 2001 as 40 CFR 197.20. We believe this approach 
maintains an appropriate emphasis on the initial condition of the 
repository and its critical early evolution, including the period when 
thermal stresses will be most significant.\6\ As the disposal system 
evolves, today's final rule establishes a peak dose standard for the 
period up to 1 million years that is responsive to the Court's ruling, 
consistent with the NAS recommendation to establish a compliance 
standard for the time of peak risk, and satisfies our statutory mandate 
to protect public health and safety. The final rule also provides a 
reasonable test of disposal system performance by appropriately 
recognizing the relatively more difficult challenge in treating the 
uncertainties associated with projecting performance to such distant 
times, and the resulting lessened level of confidence that can be 
derived from such performance projections.
---------------------------------------------------------------------------

    \6\ We noted in our 2001 rule: ``Focusing upon a 10,000-year 
compliance period forces more emphasis upon those features over 
which humans can exert some control, such as repository design and 
engineered barriers. Those features, the geologic barriers, and 
their interactions define the waste isolation capability of the 
disposal system. By focusing upon an analysis of the features that 
humans can influence or dictate at the site, it may be possible to 
influence the timing and magnitude of the peak dose, even over times 
longer than 10,000 years.'' (66 FR 32099)
---------------------------------------------------------------------------

    As we noted in our proposal, there was no legal challenge to, and 
the Court made no ruling on, the protectiveness of our standards up to 
10,000 years. Further, the Court ruled that we must address peak dose, 
but did not state, and we do not believe intended, that we could not 
have additional measures to bolster the overall protectiveness of the 
standard. We believe that promulgating the post-10,000-year peak dose 
standard to protect public health and safety while retaining a separate 
individual-protection standard that focuses attention on the early 
evolution of the repository in the pre-10,000-year period enhances the 
overall protectiveness of our rule and is consistent with the findings 
and recommendations of the NAS committee. As the Court noted, the EnPA 
requires that EPA ``establish a set of health and safety standards, at 
least one of which must include an EDE-based, individual protection 
standard'' (NEI, 373 F.3d at 1281), but does not restrict us from 
issuing additional standards. Thus, as long as we address the NAS 
recommendation regarding peak dose, as we are doing today by issuing 
the post-10,000-year standard, we are not precluded from issuing other, 
complementary, standards to apply for a different compliance period. 
The Court's concern was whether we had been inconsistent with the NAS 
recommendation by not extending the period of compliance to capture the 
peak dose ``within the limits imposed by the long-term stability of the 
geologic environment.'' (NAS Report p. 2) Today's final rule defines 
the period of geologic stability for purposes of compliance as ending 
at 1 million years after disposal. We believe our decision to retain a 
separate standard applicable for the first 10,000 years after disposal 
during this period, along with ``at least one * * * EDE-based, 
individual protection standard'' applying to the peak dose during the 
period of geologic

[[Page 61264]]

stability between 10,000 years and 1 million years, protects public 
health and safety pursuant to the EnPA, complies with the Court's 
decision, falls well within our policy discretion and is supported by 
scientific considerations concerning the impact of uncertainties in 
projecting doses over extremely long time frames, as discussed in 
Section III.A.4 of this document (``How Did We Consider Uncertainty and 
Reasonable Expectation?'').
    The NAS Report recognized the possible outcome of a rulemaking 
establishing separate standards that apply over different time periods. 
As discussed in more detail in Section III.A.6 (``How Does Our Rule 
Protect Future Generations?''), the committee contrasted an approach in 
which ``a health-based risk standard could be specified to apply 
uniformly across time and generations'' with ``some other expression of 
the principle of intergenerational equity'' to be determined by 
``social judgment.'' (NAS Report pp. 56-57) The committee also 
recognized, as we have just explained, that ``the scientific basis for 
analysis changes with time'' in potentially significant ways as the 
time to peak dose increases. (NAS Report pp. 30-31) We also find it 
useful to consider the testimony of Mr. Robert Fri, chair of the NAS 
committee, before the Senate Environment and Public Works Committee on 
March 1, 2006, in his personal capacity, wherein he pointed out that 
``the specification of the time horizon and the selection of the person 
to be protected are intimately connected.'' As a result, he explained 
that retaining the RMEI as the receptor (which the NAS committee 
recognized as more conservative than, but ``broadly consistent'' with, 
its preferred probabilistic critical group \7\) while at the same time 
extending the compliance period ``runs the risk of excessive 
conservatism,'' potentially putting the rule where the ``committee 
specifically did not want to be.'' He noted that the committee had 
considered and rejected such an approach. (See NAS Report pp. 100-103) 
Mr. Fri viewed our proposal of a higher dose limit between 10,000 and 1 
million years as a way ``to avoid becoming overly conservative.'' 
Therefore, while he (like the NAS committee itself) offered no opinion 
on the level of the proposed post-10,000-year standard, he indicated 
that, in his opinion, our approach was not in conflict with the 
committee's intention, and would be closer to the committee's overall 
goal than would applying the 15 mrem/yr standard to the 1 million-year 
compliance period. He concluded by stating ``the committee recognized 
that EPA properly had considerable discretion in applying policy 
considerations outside the scope of our study to the development of the 
health standard for Yucca Mountain.'' (See generally NAS Report p. 3) 
See the hearing transcript at Docket No. EPA-HQ-OAR-2005-0083-0380 and 
Mr. Fri's prepared testimony at Docket No. EPA-HQ-OAR-2005-0083-0402. 
We believe the decision to establish two compliance standards falls 
well within our policy discretion and in that context the 10,000-year 
individual-protection standard is analogous to our ground-water 
protection standards, which were also not addressed by NAS 
recommendations.
---------------------------------------------------------------------------

    \7\ In discussing an alternative subsistence-farmer receptor, 
the committee noted that ``it makes the most conservative assumption 
that wherever and whenever the maximum concentration of 
radionuclides occurs in a ground water plume accessible from the 
surface, a farmer will be there to access it.'' (NAS Report p. 102) 
We have defined the RMEI to incorporate this same assumption.
---------------------------------------------------------------------------

1. What Is the Peak Dose Standard Between 10,000 and 1 Million Years 
After Disposal?
    In establishing a public health and safety standard applicable at 
the time of peak dose, as required by the EnPA and recommended by the 
NAS, and after considering public comments on the issue, today's final 
rule adopts a more stringent standard than the proposed 3.5 mSv/yr (350 
mrem/yr) standard. Specifically, we are today establishing an 
individual-protection standard of 1 mSv/yr (100 mrem/yr) to apply 
beyond 10,000 years and up to 1 million years after disposal.
    As discussed in more detail later in this section, NAS expressly 
refrained from recommending any specific dose or risk limit for the 
compliance standard, but instead described ``the spectrum of 
regulations already promulgated that imply a level of risk, all of 
which are consistent with recommendations from authoritative radiation 
protection bodies'' for EPA's consideration. (NAS Report p. 49) 
Further, while NAS stated that a single standard ``could be specified 
to apply uniformly over time and generations,'' it also recognized that 
other approaches are possible as ``a matter for social judgment.'' (NAS 
Report pp. 56-57) NAS also recognized that the level of protection was 
a matter best left to EPA to establish through rulemaking: ``We do not 
directly recommend a level of acceptable risk.'' (NAS Report p. 49) NAS 
further noted that, while ``there is a considerable body of analysis 
and informed judgment from which to draw in formulating a standard for 
the proposed Yucca Mountain repository,'' ``EPA's process for setting 
the Yucca Mountain standard is presumably not bound by this 
experience.'' (NAS Report p. 39) Thus, the NAS Report contains no 
finding or recommendation as to the dose limit at the time of peak dose 
in our Yucca Mountain standards.
    In selecting this final standard, we started with a range of annual 
fatal cancer risk (10-5 to 10-6) that encompassed 
the 15 mrem/yr standard established in 2001 for the initial 10,000 
years after disposal. We also considered the ``starting range'' 
identified by NAS in determining the appropriate level for the 
individual-protection standard to apply in the time period beyond 
10,000 years. (NAS Report p. 49 and Tables 2-3 and 2-4) For the reasons 
discussed below, we determined that it would not be reasonable to apply 
a standard within that starting range for the entire million-year 
compliance period. Rather, we identified dose levels that are 
protective of public health and safety and that reasonably accommodate 
our policy concerns regarding the implementation of a compliance 
standard for 1 million years. For the same reasons, the Agency has 
determined that it is not reasonable to apply its traditional risk-
management policies when establishing a compliance standard applicable 
for periods beyond 10,000 years and up to 1 million years (see section 
III.A.3, ``How Do Our Standards Protect Public Health and Safety?''). 
EPA does not believe it is realistic to demand that projections for 
such complex systems over this far future time frame be readily 
distinguishable at the level of incremental risk customarily addressed 
by the Agency in situations where results can be confirmed, modeling is 
utilized on a more limited scale, or institutional controls are more 
applicable.
    In selecting 100 mrem/yr as the peak dose standard for the period 
beyond 10,000 years, we took particular note of the NAS's discussion of 
that dose level: ``Consistent with the current understanding of the 
related consequences, ICRP, NCRP, IAEA, UNSCEAR, and others have 
recommended that radiation doses above background levels to members of 
the public not exceed 1 mSv/yr (100 mrem/yr) effective dose for 
continuous or frequent exposure from radiation sources other than 
medical exposures. Countries that have considered national radiation 
protection standards in this area have endorsed the ICRP recommendation 
of 1 mSv per year radiation dose limit above natural background 
radiation for members of

[[Page 61265]]

the public.'' (NAS Report pp. 40-41) We also note that the 100 mrem/yr 
level is included in the range of regulations offered by NAS for EPA's 
consideration. (NAS Report Table 2-3)
    Therefore, as we discussed in our proposal, a dose level of 100 
mrem/yr level is well-established as protective of public health under 
current dose limits, and, as such, represents a robust public health 
protection standard in the extreme far future. (70 FR 49040) As noted 
by NAS, international organizations such as ICRP, IAEA, and NEA 
recommend its use as an overall public dose limit in planning for 
situations where exposures may be reasonably expected to occur. 
Although it had used the concept of public dose limits previously, ICRP 
first described its recommendations for a comprehensive system of 
radiation protection in Publication 60 (``1990 Recommendations of the 
ICRP'') (Docket No. EPA-HQ-OAR-2005-0083-0421). ICRP considered two 
referents in recommending a public dose limit: health detriment and 
``variation in the existing level of dose from natural sources.'' ICRP 
concluded that estimates of health detriment ``suggest a value of the 
annual dose limit not much above 1 mSv.'' Similarly, ``[e]xcluding the 
very variable exposures to radon, the annual effective dose from 
natural sources is about 1 mSv, with values at high altitudes above sea 
level and in some geological areas of at least twice this. On the basis 
of all these considerations, the Commission recommends an annual limit 
on effective dose of 1 mSv.'' (Paragraphs 190-191) ICRP re-affirmed 
this position in its most recent recommendations: ``For public exposure 
in planned exposure situations, the Commission continues to recommend 
that the limit should be expressed as an effective dose of 1 mSv in a 
year.'' (Publication 103, Paragraph 245, Docket No. EPA-HQ-OAR-2005-
0083-0423)
    This recommendation as to a 100 mrem/yr public dose limit was 
adopted in the 1996 ``International Basic Safety Standards for 
Protection Against Ionizing Radiation and for the Safety of Radiation 
Sources,'' which was jointly sponsored by IAEA, NEA, the Food and 
Agriculture Organization of the United Nations, the International Labor 
Organization, the Pan American Health Organization, and the World 
Health Organization. (IAEA Safety Series 115, Schedule II, Docket No. 
EPA-HQ-OAR-2005-0083-0409) It should also be noted that the European 
Union requires its Member States to incorporate this 100 mrem/yr public 
dose limit into national law or regulation (Council Directive 96/29/
EURATOM of 13 May 1996, Docket No. EPA-HQ-OAR-2005-0083-0410). Non-EU 
countries such as Argentina, Australia, Canada, and Japan also 
incorporate this public dose limit into their systems of regulation, as 
shown by their national reports under the Joint Convention on the 
Safety of Spent Fuel Management and on the Safety of Radioactive Waste 
Management (see http://www-ns.iaea.org/conventions/waste-
jointconvention.htm). The United States is also a Contracting Party to 
the Joint Convention (Docket No. EPA-HQ-OAR-2005-0083-0393).
    Domestically, both NRC and DOE incorporate the 100 mrem/yr level 
into their systems of regulation (10 CFR 20.1301 and DOE Order 5400.5, 
respectively), and NCRP also endorses the ICRP system of protection 
(NCRP Report 116, ``Limitation of Exposure to Ionizing Radiation,'' 
Docket No. EPA-HQ-OAR-2005-0083-0407). In setting today's peak dose 
standard, EPA acknowledges and concurs in the broad consensus in the 
protectiveness of the 100 mrem/yr level and, furthermore, considers it 
especially suitable for application to the extreme far future, when 
planning for and projecting public exposures is much less certain.
    For all these reasons, we conclude that the 100 mrem/yr peak dose 
standard we are establishing today for the period beyond 10,000 years 
will protect public health and safety. By considering international 
guidance and examples, we have derived a final peak dose limit that 
balances the competing factors highlighted by NAS and acknowledged by 
us as important: the dual objectives of promulgating a standard that is 
protective of the health and interests of future generations, and also 
effectively addressing the effects of uncertainty on compliance 
assessment. Moreover, the 100 mrem/yr level is comparable to the 
domestic and international standards NAS suggested that EPA consider. 
(NAS Report p. 49 and Tables 2-3 and 2-4)
    Our selection of a 100 mrem/yr standard is therefore protective and 
reasonable in that it effectively addresses the factors it is necessary 
to consider when projecting exposures very far into the future. By 
applying this standard over the entire period of geologic stability 
beyond 10,000 years (up to 1 million years), our approach is consistent 
with the NAS recommendation to have a standard with compliance measured 
``at the time of peak risk, whenever it occurs, within the limits 
imposed by the long-term stability of the geologic environment, which 
is on the order of one million years.'' (NAS Report p. 2)
    Although we have not used specific estimates of background 
radiation in determining our final peak dose standard, as we had 
proposed, we note that the 100 mrem/yr level reasonably comports with 
such an analysis as well. For example, it is comparable to outdoor 
(unshielded) measurements of cosmic and terrestrial radiation in 
Amargosa Valley. When shielding from buildings is considered and indoor 
radon doses are estimated using a more conservative conversion factor 
suggested by some commenters, 100 mrem/yr is at the low end of overall 
background radiation estimates in Amargosa Valley and nationally.\8\ 
Within the State of Nevada, the difference in average estimates of 
background radiation for counties is greater than 100 mrem/yr. (Docket 
No. EPA-HQ-OAR-2005-0083-0387) This suggests that 100 mrem/yr can be 
considered to be a level such that the total potential doses incurred 
by the RMEI from the combination of background radiation and releases 
from Yucca Mountain will remain below doses incurred by residents of 
other parts of the country from natural sources alone. See Section 
III.A.5 of this document for more discussion of background radiation 
(``How Did We Consider Background Radiation in Developing the Peak Dose 
Standard?'').
---------------------------------------------------------------------------

    \8\ NAS cited an estimate of 300 mrem/yr as the national average 
for natural background radiation (cosmic, terrestrial, radon, and 
radioactive isotopes internal to the human body). (NAS Report Table 
2-1) This is the best-known estimate of average natural background 
in the U.S., but does not use the more conservative radon dose 
conversion factor provided by public comments.
---------------------------------------------------------------------------

    Our proposal discussed several factors that we considered to be 
important in setting a dose standard for the time of peak dose within 
the period of geologic stability. We emphasized the cumulative and 
increasing uncertainty in projecting potential doses over great time 
periods, and argued against viewing projected doses as predictions of 
disposal system performance. This is consistent with the position taken 
by the NAS committee: ``The results of compliance analysis should not, 
however, be interpreted as accurate predictions of the expected 
behavior of a geologic repository.'' (NAS Report p. 71)
    We also have considered how the role of quantitative projections in 
making compliance decisions must change as the time covered by those 
projections increases to the extreme far future. We noted that 
emphasizing incremental dose increases when such increases may be 
overwhelmed by fundamental uncertainties inappropriately takes 
attention away from an evaluation of the

[[Page 61266]]

overall safety of the disposal system, which may rest equally on other 
lines of evidence, such as confidence in the long-term stability of the 
site or reference to natural analogues. In our view, in order to 
provide a reasonable test of the disposal system, the role of the peak 
dose standard in the overall decision of disposal system safety must be 
consistent with the relative confidence that can be placed in 
quantitative projections over extremely long times. We have recognized 
the strong consensus in the international radioactive waste community 
that dose projections extending many tens to hundreds of thousands of 
years into the future can best be viewed as qualitative indicators of 
disposal system performance, rather than as firm predictions that can 
be compared against strict numerical compliance criteria. In fact, 
international organizations have treated such numerical criteria in a 
more flexible way and supported their application in conjunction with 
other qualitative considerations in applying them to regulatory 
determinations over very long time frames.\9\ Further, we agree that 
confidence in the way the projections were performed, and the 
consideration of supporting qualitative information, may be more 
important to an overall judgment of safety at longer times.\10\ 
However, our task is to establish a numerical compliance limit, rather 
than a qualitative standard or dose target. Therefore, we believe it is 
appropriate in setting that limit to evaluate and apply the 
considerations that have led the international radiation protection 
community to view long-term projections in a more qualitative manner.
---------------------------------------------------------------------------

    \9\ The 2007 NEA document on ``Consideration of Timescales in 
Post-Closure Safety of Geological Disposal of Radioactive Waste,'' 
which is based on surveys of NEA Member Countries, states 
``Calculated values of dose and risk are therefore viewed in 
regulations not as predictions but rather as indicators or measures 
of protection that are used to test the capability of the system to 
provide isolation of the waste and containment of radionuclides (the 
`dose' that is being calculated is what radio-protectionists refer 
to as `potential dose'). These indicators are to be evaluated on the 
basis of models that include certain stylized assumptions, in 
particular regarding the biosphere and human lifestyle or actions.'' 
(Docket No. EPA-HQ-OAR-2005-0083-0411, p. 38) NEA also notes: 
``There is agreement that calculations of dose and risk in the 
future are illustrations of possible system behaviour rather than 
predictions of outcomes, and there is consensus that, in the long 
term, numerical criteria for radioactive waste disposal should be 
considered as references or indicators, addressing the ultimate 
safety objectives, rather than as absolute limits in a legal 
context.'' (``Regulating the Long-Term Safety of Geological 
Disposal: Towards a Common Understanding of the Main Objectives and 
Bases of Safety Criteria,'' NEA-6182, Docket No. EPA-HQ-OAR-2005-
0083-0408, p. 24) Similarly, ICRP Publication 81 contrasts the 
approach of ``consideration of quantitative estimates of dose or 
risk on the order of 1000 to 10,000 years'' with ``consideration of 
quantitative calculations further into the future making increasing 
use of stylized approaches and considering the time periods when 
judging the calculated results. Qualitative arguments could provide 
additional information to this judgmental process.'' (Docket No. 
EPA-HQ-OAR-2005-0083-0417, Paragraph 71) The IAEA consensus document 
for geologic disposal (``Safety Requirements for Geological Disposal 
of Radioactive Waste,'' WS-R-4, 2006) states: ``It is recognized 
that radiation doses to individuals in the future can only be 
estimated and that the uncertainties associated with these estimates 
will increase for times farther into the future. Care needs to be 
exercised in using the criteria beyond the time when the 
uncertainties become so large that the criteria may no longer serve 
as a reasonable basis for decisionmaking.'' (Docket No. EPA-HQ-OAR-
2005-0083-0383, Paragraph 2.12)
    \10\ Such considerations are not unusual in other applications. 
For example, in making plans based on weather forecasts, one can 
expect the next-day forecast to be fairly accurate. However, one has 
to recognize that the same degree of accuracy cannot be expected 
from longer-range forecasts. In that case, one would want to have 
confidence that the forecast is based upon the most current 
scientific understanding of weather patterns.
---------------------------------------------------------------------------

    We conclude that a peak dose standard of 100 mrem/yr for the Yucca 
Mountain disposal system for the period between 10,000 and 1 million 
years protects public health and safety. Setting the standard as we 
have is also consistent with the NAS committee's decision not to 
recommend a level for the final peak standard and EPA's broad 
discretion to establish standards that are protective while 
accommodating technical and policy concerns inherent in projecting and 
evaluating potential events hundreds of thousands of years into the 
future. See section III.A.3 of this document for more discussion of the 
protectiveness of our standards (``How Does Our Final Rule Protect 
Public Health and Safety?'').
    The ICRP recommendation for a public dose limit of 100 mrem/yr 
relates to the total exposure to members of the public from all manmade 
sources (excluding occupational, accidental, and medical, which can be 
significantly higher). A number of comments took issue with our 
approach and suggestion that it might be reasonable to ``apportion'' 
the entire 100 mrem/yr to the Yucca Mountain disposal system because of 
the lack of other potential sources in the region, and that this could 
be considered consistent with the NAS recommendation to rely on current 
conditions and present knowledge. The comments expressed the view that 
such an approach would be entirely contrary to the NAS recommendation 
to apply apportionment, as well as to the principle of apportionment 
itself, which recognizes the potential for new or additional sources of 
exposure to be developed.
    NAS made no recommendation or finding regarding apportionment. In 
its discussion of apportionment, NAS noted that the concept had been 
widely adopted (NAS Report pp. 40-41). NAS also noted that ``guidance 
to date has been for expected exposures from routine practices. There 
is little guidance on potential exposures in the far distant future.'' 
(NAS Report p. 41). NAS made no specific recommendation that EPA apply 
the concept to Yucca Mountain, let alone how the concept should be 
applied.
    Further, given our statutory obligation under the EnPA to establish 
a site-specific standard, allocating 100 mrem/yr to a single source at 
the time of peak dose is reasonable because other contributors 
currently in the Yucca Mountain area are negligible by comparison 
(FEIS, DOE/EIS-0250, section 8.3.2, Docket No. EPA-HQ-OAR-2005-0083-
0086). By relying on current conditions, as recommended by NAS, rather 
than speculating on potential future sources of exposure to the local 
population, it is reasonable for EPA to allocate the entire 100 mrem/yr 
to the Yucca Mountain disposal system. By assuming that current 
conditions will apply in the future, we are applying an approach 
routinely applied internationally, as well as by EPA in its WIPP 
compliance criteria (the ``future states'' assumption at 40 CFR 
194.25).\11\
---------------------------------------------------------------------------

    \11\ For example, IAEA notes that in modeling over longer time 
frames, ``The emphasis of assessment should therefore be changed so 
that the calculations relating to the near-surface zone and human 
activity are simplified by assuming present day communities under 
present conditions.'' (TECDOC-767, Docket No. EPA-HQ-OAR-2005-0083-
0044, p. 19) The French Basic Safety Rule III.2.f specifies that 
``The characteristics of man will be considered to be constant 
(sensitivity to radiation, nature of food, contingency of life, and 
general knowledge without assuming scientific progress, particularly 
in the technical and medical fields).'' (Docket No. EPA-HQ-OAR-2005-
0083-0389, Section 3.2)
---------------------------------------------------------------------------

    EPA's application of the concept of apportionment is, moreover, 
reasonable. We addressed the apportionment approach in conjunction with 
our 10,000-year standard of 15 mrem/yr as consistent with EPA's overall 
risk management approach and past actions. However, we do not agree 
that it is either required or reasonable to follow the apportionment 
approach over hundreds of thousands of years, when the level of 
uncertainty in dose projections is significantly increased and the 
ability to project the performance of engineered barriers and the 
overall disposal system with a high degree of certainty decreases. This 
position is consistent with general

[[Page 61267]]

international practice and guidance, in which regulatory judgments rely 
less on compliance with quantitative standards and more on other 
qualitative factors supporting the overall safety case. Thus, for 
example, IAEA recognizes in the consensus document ``Safety 
Requirements for Geological Disposal of Radioactive Waste'' (WS-R-4, 
Docket No. EPA-HQ-OAR-2005-0083-0383) the general agreement of the 
geologic disposal community that, while apportionment is pertinent to 
geologic disposal, it cannot be assumed to apply indefinitely.\12\ 
Moreover, IAEA reaches this conclusion on the basis of uncertainty in 
projecting exposure from a specific long-term source, without regard to 
the presumed knowledge, or lack thereof, of other potential sources of 
exposure. We believe our approach is consistent with the long-held 
international view of 10,000 years generally as a demarcation point 
prior to which quantitative dose projections can be reasonably well-
managed, but beyond which those projections become progressively more 
uncertain and less valuable.\13\ In our view, it is preferable to 
follow this well-established precedent rather than to attempt to define 
a different transition point based on the level and timing of 
uncertainty in dose projections. As discussed in more detail later in 
this section, countries that have established dose or risk standards 
for geologic disposal have typically applied them for 10,000 years or 
less, suggesting that this is a period of time within which standards 
comparable to those applied to current practices can ``serve as a 
reasonable basis for decision making.'' Beyond that time, the initial 
``criteria,'' or dose standards, are viewed more qualitatively or 
entirely different criteria that are not expressed in terms of risk or 
dose are applied.\14\
---------------------------------------------------------------------------

    \12\ In describing criteria relevant to apportionment, IAEA 
states: ``It is recognized that radiation doses to individuals in 
the future can only be estimated and that the uncertainties 
associated with these estimates will increase for times farther into 
the future. Care needs to be exercised in using the criteria beyond 
the time when the uncertainties become so large that the criteria 
may no longer serve as a reasonable basis for decision making.'' 
(Paragraph 2.12, emphasis added) Similarly, NEA cites IAEA and ICRP 
in noting that ``Generally speaking, these documents recommend that 
the same criteria should be used as are applied for radiation 
protection from current practices. These documents also recognise, 
however, that such criteria cannot be applied in the same way for 
the distant future as they are for current practices.'' (NEA-6182, 
Docket No. EPA-HQ-OAR-2005-w0083-0408, p. 19, emphasis added)
    \13\ ICRP clearly expresses this view in Publication 81: ``To 
evaluate the performance of waste disposal systems over long time 
scales, one approach is the consideration of quantitative estimates 
of dose or risk on the order of 1000 to 10,000 years. This approach 
focuses on that period when the calculation of doses most directly 
relates to health detriment and also recognises the possibility that 
over longer time frames the risks associated with cataclysmic 
geologic changes such as glaciation and tectonic movements may 
obscure risks associated with the disposal system. Another approach 
is the consideration of quantitative calculations further into the 
future making increased use of stylised approaches and considering 
the time periods when judging the calculated results. Qualitative 
arguments could provide additional information to this judgmental 
process.'' (Docket No. EPA-HQ-OAR-2005-0083-0417, Paragraph 71) 
Similarly, IAEA suggests that within 10,000 years, ``While it is 
recognized that considerable uncertainty can exist during this time 
period, it is still reasonable to attempt to make quantitative 
estimates of the indicators to be used.'' However, beyond that time, 
``While it may be possible to make general predictions about 
geological conditions, the range of possible biospheric conditions 
and human behaviour is too wide to allow reliable modeling * * * 
Such calculations can therefore only be viewed as illustrative and 
the `doses' as indicative.'' (``Safety Indicators in Different Time 
Frames for the Safety Assessment of Underground Radioactive Waste 
Repositories,'' TECDOC-767, Docket No. EPA-HQ-OAR-2005-0083-0044, 
pp. 18-19)
    \14\ France applies a dose standard for the first 10,000 years 
that ``will be applied for determining the acceptability of the 
radiological consequences.'' However, at later times, ``the same [25 
mrem/yr] limit shall be used as a reference value.'' (Basic Safety 
Rule III.2.f, Section 3.2.1, Docket No. EPA-HQ-OAR-2005-0083-0389, 
emphasis added) Sweden specifies quantitative analyses to be judged 
against a numerical standard for the first 1,000 years, but requires 
examination of ``various possible sequences for the development of 
the repository's properties, its environment and the biosphere'' 
after that time. (SSI FS 1998:1, Docket EPA-HQ-OAR-2005-0083-0047) 
Similarly, Finland applies a dose standard for ``at least several 
thousands of years,'' but when ``human exposure'' is no longer 
``adequately predictable,'' an activity release standard is in 
place. (YVL 8.4, Docket EPA-HQ-OAR-2005-0083-0392)
---------------------------------------------------------------------------

    Moreover, we note that under 10 CFR 20.1301, NRC requires that 
licensees conduct operations so that the total effective dose 
equivalent to individual members of the public from ``the licensed 
operation'' does not exceed 100 mrem/yr. Thus, this regulatory limit 
applies to individual licensees operating today, without reference to 
other potential sources of exposure to the public. Of course, some 
types of NRC licensees, such as fuel cycle facilities subject to our 
standards in 40 CFR part 190, must meet dose constraints lower than the 
100 mrem/yr limit. Nonetheless, 100 mrem/yr is the public dose limit 
from licensed operations imposed in NRC regulations.
    We disagree with those comments generally questioning both the 
legality and the protectiveness of our proposal to establish a long-
term standard higher than 15 mrem/yr. As described previously in 
section III.A (``What Dose Standards Will Apply?''), commenters stated 
that the NAS Report and Court decision required us to retain a single 
dose standard (i.e., 15 mrem/yr) for the entire 1 million-year 
compliance period, equivalent to the period of geologic stability 
defined in our rule. Commenters pointed out that the proposed level was 
well above the range identified by NAS as a starting point for our 
rulemaking, and therefore stated that only the 15 mrem/yr level could 
be considered consistent with the committee's recommendation. 
Similarly, some commenters interpreted the Court ruling to require us 
to adjust the time period covered by the existing 15 mrem/yr standard, 
which was not challenged. We do not believe this interpretation to be 
correct. It should be emphasized that NAS identified a range of risks 
represented by current national and international standards, ``all of 
which are consistent with recommendations from authoritative radiation 
protection bodies,'' suggested only a ``reasonable starting point'' for 
our rulemaking, and that none of the regulatory precedents considered 
by NAS applied for periods approaching 1 million years. (NAS Report pp. 
5 and 49, respectively) In fact, NAS explicitly declined to recommend a 
level of protection, recognizing that this was a matter best left to 
EPA to establish through rulemaking: ``We have not recommended what 
levels of risk are acceptable * * * The specific level of acceptable 
risk cannot be identified by scientific analysis, but must rather be 
the result of a societal decision-making process. Because we have no 
particular authority or expertise for judging the outcome of a properly 
constructed social decision-making process on acceptable risk, we have 
not attempted to make recommendations on this important question.'' 
(NAS Report p. 20) Indeed, NAS explicitly acknowledged ``that 
determining what risk level is acceptable is not ultimately a question 
of science but of public policy.'' (NAS Report p. 5) Further, NAS noted 
that the final outcome of the rulemaking might diverge substantially 
from the starting point suggested by NAS: ``Finally we have identified 
several instances where science cannot provide all of the guidance 
necessary to resolve an issue * * * In these cases, we have tried to 
suggest positions that could be used by the responsible agency in 
formulating a proposed rule. Other starting positions are possible, and 
of course the final rule could differ markedly from any of them.'' (NAS 
Report p. 3, emphasis added) Thus, we agree with NAS that the selection 
of a level for the peak dose standard is one of the regulatory policy 
issues left to EPA's discretion by the EnPA. As stated earlier, we find 
that the annual risk associated with the final peak dose standard of 
100 mrem/yr is

[[Page 61268]]

protective of public health and comparable to the domestic and 
international standards NAS suggested that EPA consider, particularly 
when considering the extended time frames under consideration for this 
rulemaking. (NAS Report p. 49 and Tables 2-3 and 2-4)
    We also find it instructive to consider again the personal Senate 
testimony of NAS committee chair Robert Fri, as described in Section 
III.A (``What Dose Limits Will Apply?'') (Docket Nos. EPA-HQ-OAR-2005-
0083-0380 and 0402). Mr. Fri noted that simply extending the compliance 
period in our 2001 rule to 1 million years ``runs the risk of excessive 
conservatism'' and could place our standard where the ``committee 
specifically did not want to be.'' He recognized that a higher standard 
at the time of peak dose would be one way to reduce that conservatism. 
Mr. Fri did not address the consistency of our proposed dose level with 
the NAS findings and recommendations; however, he indicated that, in 
his view, retaining the 15 mrem/yr standard at the time of peak dose 
would not be consistent with those findings and recommendations if 
other aspects of our rule remained unchanged (specifically, the choice 
of receptor). We find this perspective noteworthy, in that it suggests 
that there are circumstances in which applying 15 mrem/yr throughout 
the 1 million-year compliance period could result in a standard 
contrary to the committee's overall goals, which emphasized the use of 
``cautious, but reasonable'' assumptions and care in the use of 
``pessimistic scenarios and parameter values.'' (NAS Report pp. 100 and 
79, respectively)
    Further, we do not believe the Court's decision provides direction 
independent of the NAS Report; rather, the decision requires only that 
we ensure that our standards are consistent with the NAS committee's 
findings and recommendations, as required by the EnPA.
    In considering appropriate dose standards for periods approaching 1 
million years, we also considered the development of our generic 
standards in 40 CFR part 191. In both our 1985 and 1993 rulemakings 
establishing those generic standards, we emphasized that the 10,000-
year compliance period for both the containment requirements and 
individual-protection limit would lead to a combination of site 
characteristics and engineered barriers that would be capable of 
providing containment and isolation of the waste for these long periods 
of time. We did not, however, anticipate that such performance could be 
maintained indefinitely. Our generic technical analyses, in fact, 
suggested that significant releases and doses to individuals could 
result at later times, depending on the characteristics of the site in 
question and the presumed location of the receptor. (See 58 FR 66401, 
December 20, 1993)
    We note that sites whose natural features alone did not provide 
total containment were not necessarily considered unsuitable, but we 
recognized that in those instances, the focus would have to be on ``the 
design of more robust engineered barrier systems capable of 
significantly impeding radionuclide releases.'' We believe that it is 
unrealistic to assume that these sites would then exhibit better 
performance after the failure of those barriers than they would in the 
initial 10,000-year period. Consequently, we believe that the potential 
for doses higher than 15 mrem/yr to individuals in the far future has 
always been implicit in the concept of geologic disposal. Over time, 
the initial static system consisting of intact waste packages and other 
engineered barriers in the natural geologic setting gives way to a more 
dynamic system in which episodic and gradual processes combine to 
transport radionuclides to the accessible environment. The sequence and 
timing of barrier failures strongly influence, and introduce 
considerable uncertainty into, the timing and magnitude of projected 
doses over the 1 million-year period. The range of projected doses 
widens considerably as the containment capability of the engineered 
barriers diminishes. Interpreting the safety of the disposal system for 
regulatory purposes, in our judgment, involves more than comparison of 
projected doses to a regulatory standard, and a single standard 
applicable to the initial static system would not adequately capture 
the essential nature of a system that will evolve over 1 million years.
    In developing our final standards, we have given much attention to 
guidance from international organizations and examples from specific 
national programs. In general, we find few similarities in the details 
of the international approaches that are directly applicable, and no 
clear basis for comparing the different approaches. At the same time, 
we did find broad points of similarity in the overall approach to long-
term projections, and referred in our proposal to organizations such as 
IAEA and NEA, as well as specific countries, such as Sweden. The more 
typical approach internationally is to require compliance with 
quantitative performance assessment for only a limited period of time 
(in some cases, less than 10,000 years). Longer-term dose projections 
may be compared to dose or risk targets or reference levels, but are 
viewed more as qualitative indicators of performance than as ``accurate 
predictions of the expected behavior of a geologic repository'' (NAS 
Report p. 71), to be weighed in conjunction with other qualitative 
arguments for confidence in the overall safety of the facility. At 
longer times, the weight given to quantitative projections typically 
decreases.\15\ More detailed discussion of specific international 
approaches may be found in Section 4 of the Response to Comments 
document for this final rule (Docket No. EPA-HQ-OAR-2005-0083-0431).
---------------------------------------------------------------------------

    \15\ The standard issued by the Swedish Radiation Protection 
Authority (SSI, formerly the Swedish Radiation Protection Institute) 
(SSI FS 1998:1, ``Regulations on the Protection of Human Health and 
the Environment in Connection with the Final Management of Spent 
Nuclear Fuel and Nuclear Waste,'' Docket EPA-HQ-OAR-2005-0083-0047) 
includes a numerical standard during the initial period after 
disposal and adopts a more qualitative approach at later times. 
Specifically, for the first 1,000 years following closure of a 
repository, ``the assessment of the repository's protective 
capability shall be based on quantitative analyses of the impact on 
human health and the environment.'' (Section 11) Thus, initially the 
performance projections may be used to make decisions regarding the 
protectiveness of the disposal system. However, beyond the first 
thousand years, ``the assessment of the repository's protective 
capability shall be based on various possible sequences for the 
development of the repository's properties, its environment and the 
biosphere.'' (Section 12) Similarly, the Finnish Radiation and 
Nuclear Safety Authority's (STUK) regulations for ``Long-term Safety 
of Disposal of Spent Nuclear Fuel'' (YVL 8.4, May 2001, Docket EPA-
HQ-OAR-2005-0083-0392) include two primary protection standards. The 
first is an individual-protection standard of 10 mrem/yr (0.1 mSv/
yr), which applies to ``an assessment period that is adequately 
predictable with respect to assessments of human exposure but that 
shall be extended to at least several thousands of years.'' (Section 
2.2) The second protection standard, which is implied to cover 
periods beyond the time for which ``human exposure'' is ``adequately 
predictable,'' is a radionuclide release standard similar to that 
included in 40 CFR part 191 and applied at WIPP. We also refer 
readers to the French standard (Basic Safety Rule No. III.2.f, 
``Disposal of Radioactive Waste in Deep Geological Formations,'' 
1991, Docket No. EPA-HQ-OAR-2005-0083-0389). For the initial period, 
which is to last ``at least 10,000 years * * * The limit of [25 
mrem/yr] will be applied for determining the acceptability of the 
radiological consequences.'' However, ``[b]eyond this period'' when 
``uncertainty concerning the evolution of the repository increases 
progressively with time * * * Quantified estimates of the individual 
dose estimates must then be made. These may be supplemented, by more 
qualitative assessments of the results of these estimates, as 
regards the geological barrier evolution factors, so as to verify 
that the release of the radionuclides does not result in an 
unacceptable individual dose. In this verification, the same [25 
mrem/yr] limit shall be used as a reference value.'' (Section 3.2.1, 
emphasis added)

---------------------------------------------------------------------------

[[Page 61269]]

2. What is the Dose Standard for 10,000 Years After Disposal?
    Section 801(a)(1) of the EnPA directs us to ``promulgate, by rule, 
public health and safety standards'' that ``prescribe the maximum 
annual effective dose equivalent to individual members of the public'' 
from releases of radioactive material from the Yucca Mountain 
repository. Promulgation of the standard described in section III.A.1 
of this document, which will apply beyond 10,000 years and up to 1 
million years, fulfills this statutory direction. Today's final rule 
also retains the standard promulgated in 2001 as Sec.  197.20, which 
requires that DOE demonstrate a reasonable expectation that the RMEI 
will not incur annual doses greater than 15 mrem from releases of 
radionuclides from the Yucca Mountain disposal system for 10,000 years 
after disposal. We believe this is an appropriate exercise of our 
policy discretion, protective of public health and safety, and 
consistent with our generic standards at 40 CFR part 191 (now applied 
to the WIPP) and other applications in both our regulations for 
hazardous materials and internationally for radioactive waste. Further, 
this dose level is also within the range of risks identified by NAS as 
consistent with current national and international regulations. (NAS 
Report p. 49, Tables 2-3 and 2-3) Moreover, the 15 mrem/yr standard for 
10,000 years is consistent with EPA's overall risk management policies 
\16\ and serves as a logical foundation for us to incorporate concerns 
regarding far future projections (such as the specifications regarding 
seismic, igneous, and climatic events and processes discussed in 
section III.B of this document).
---------------------------------------------------------------------------

    \16\ The annual fatal cancer risk of 15 mrem is 8.6 x 
10-6, based on a conversion factor of 5.75 x 
10-4 fatal cancers per rem.
---------------------------------------------------------------------------

    As we stated in our proposal, an important reason for retaining a 
standard applicable for the first 10,000 years is to address the 
possibility, however unlikely, that significant doses could occur 
within 10,000 years, even if the peak dose occurs significantly later, 
as NAS believed likely. (NAS Report p. 2) We received some comments 
suggesting that DOE's estimates of waste package performance are overly 
optimistic and that significant early package failures are possible, if 
not to be expected. Some commenters incorrectly argued that we had 
inappropriately ``ratified'' DOE's projections of waste package 
performance and our proposal ``would provide essentially no protection 
for the period before 10,000 years,'' because early failure of a system 
licensed against a post-10,000-year dose standard in excess of 15 mrem/
yr would have greater consequences than would early failure of a system 
licensed against a 15 mrem/yr standard that applied at all times. We 
recognize that DOE's estimates of waste package integrity rely heavily 
on extrapolations of laboratory testing data, which involve significant 
uncertainties, especially when considering time frames well in excess 
of all practical experience. It is not possible to claim unequivocally 
that no information will come to light that might cause a reassessment 
of the containers' behavior and its effect on disposal system 
performance. However, while DOE must defend its estimates in licensing, 
our rulemaking is not dependent on resolution of this issue. DOE will 
have to demonstrate that there is a reasonable expectation that the 
dose to the RMEI will not exceed 15 mrem/yr in the first 10,000 years 
after closure. Thus, the addition of the peak dose standard in no way 
weakens the protection provided by our 2001 standards, since disposal 
system performance must still be assessed against the 15 mrem/yr limit 
during the relevant time period.
    In fact, the reverse is true. The peak dose standard adds a new 
level of public health protection for the post-10,000-year period that 
was not defined in our 2001 standards. It may in fact be highly 
unlikely, if not impossible, for projected doses to exceed (or even 
approach) 15 mrem/yr within the first 10,000 years without also 
exceeding 100 mrem/yr at some other time during the compliance period 
(see section III.A.4, ``How Did We Consider Uncertainty and Reasonable 
Expectation?''). In that case, the peak dose standard of 100 mrem/yr 
alone would provide the necessary public health protection at all times 
during the compliance period. The 10,000-year standard would not, then, 
control projected doses during that period but would instead represent 
an explicit statement of the level of performance that is required to 
be achieved by the peak dose standard in that initial period. We 
believe it is important to structure our regulations to make it clear 
that the standard of protection at Yucca Mountain would not be less 
than that provided for WIPP or the Greater Confinement Disposal 
facility (GCD).\17\
---------------------------------------------------------------------------

    \17\ GCD is a group of 120-feet deep boreholes, located within 
the Nevada Test Site, which contain disposed transuranic wastes.
---------------------------------------------------------------------------

3. How Do Our Standards Protect Public Health and Safety?
    The peak dose standard we are establishing today, 1 mSv/yr (100 
mrem/yr), will protect public health and safety for the period beyond 
10,000 years and up to 1 million years. This standard is consistent 
with the public dose limit recommended by ICRP and widely adopted 
internationally and nationally. Section 801(a)(1) of the EnPA directs 
us to ``promulgate, by rule, public health and safety standards'' that 
``prescribe the maximum annual effective dose equivalent to individual 
members of the public'' from releases of radioactive material from the 
Yucca Mountain repository. In promulgating these standards, we have 
given special consideration to the EnPA mandate that our standards be 
``based upon and consistent with'' the recommendations of the NAS, 
which included setting a ``health-based individual standard'' ``that 
sets a limit on risk to individuals of adverse health effects.'' (NAS 
Report pp. 65 and 4) We understand this to mean that we should select 
the standard based, in part, on the level of risk, although NAS 
declined to recommend such a level. (NAS Report p. 49) We have chosen 
to express the standard in terms of dose, for the reasons described in 
our 2001 final rulemaking (66 FR 32085-32086). In that rulemaking, we 
did consider both the NAS views on risk and EPA policies and precedents 
in establishing the dose standard. The risk associated with the 15 
mrem/yr standard applicable for the initial 10,000-year period is 
consistent with both the Agency's overall risk management policies and 
the suggested NAS ``starting point'' (NAS Report p. 49) The nominal 
annual risk associated with the final peak dose standard of 100 mrem/
yr, 5.75 x 10-5, is comparable to the range of risks 
represented by domestic and international standards that NAS suggested 
for EPA to consider.\18\ This is a protective level of risk given the 
extremely long time frames contemplated for this standard, and 
reasonable in that it effectively addresses the associated uncertainty 
in projecting doses for up to 1 million years. Given this fact and the 
broad consensus regarding 100 mrem/yr as a protective public dose 
limit, EPA finds that the dose standard of 100 mrem/yr, with its 
associated risk, is protective of the RMEI over the period from 10,000

[[Page 61270]]

years to 1 million years, as required by the EnPA.
---------------------------------------------------------------------------

    \18\ This document focuses on annual risk rather than lifetime 
risk because NAS identified annual risk as the appropriate metric, 
although it did not recommend a particular risk level.
---------------------------------------------------------------------------

    The Agency believes it important to emphasize two aspects of this 
decision. First, modeling of a complex system such as the Yucca 
Mountain disposal system over such time frames involves significant 
uncertainties in both the knowledge of characteristics of the site and 
the conceptual representation of the processes contributing to release 
and transport of radionuclides. The NAS recommendation has extended the 
application of regulatory judgment beyond the period when substantially 
complete containment might reasonably be provided, and through a period 
during which complete loss of containment cannot be discounted. The 
sequence and timing of scenarios resulting in waste package failure are 
highly dependent on initial assumptions and are the most significant 
factors in estimating the timing and magnitude of doses to the RMEI. 
Dose projections involve extrapolation of assumptions, models, and data 
over time periods much longer than those considered in other regulatory 
contexts. Such projections therefore cannot be confirmed in the usual 
sense (i.e., through measurements or monitoring), nor is it expected 
that long-term maintenance of the repository will be performed. Such 
considerations lead us to conclude that it would not be realistic to 
demand that projections from such complex systems be readily 
distinguishable from one another at the level of incremental risk 
customarily addressed by the Agency in situations where results can be 
confirmed, modeling is utilized on a more limited scale, or 
institutional controls are more applicable.
    The Agency's second concern is the correlation of risk with health 
detriment. NAS specifically framed its recommendation to establish a 
risk standard in the context of health effects. (NAS Report pp. 4 and 
65) In doing so, it explicitly extended the traditional reliance on 
``present knowledge'' in the framing of performance assessments to 
assume that future societies would not have eliminated radiation cancer 
risks.\19\ (NAS Report p. 100) However, the reliance on risk to express 
the results of long-term safety assessments has been approached more 
cautiously, and it has primarily been viewed as a mechanism to 
incorporate the likelihood of scenarios affecting potential exposures, 
rather than as a direct measure of health impacts or as a firm 
compliance criterion.\20\
---------------------------------------------------------------------------

    \19\ Dose can be converted to risk by use of either 
radionuclide-specific or overall conversion factors. The NAS 
committee referred only to overall conversions (i.e., risk per rem), 
which is the typical approach applied to dose standards when the 
specific mix of radionuclides is not well-defined in advance. The 
committee saw the direct use of risk as an advantage if the 
relationship should change in the future through new research on 
low-dose health effects, because the underlying risk could be viewed 
as representing the level of societal acceptance of health impacts, 
which the committee saw as less likely to change, whereas dose could 
become further removed from this level of societal acceptance. (NAS 
Report p. 64) In fact, we use a conversion factor slightly higher 
than that cited by the NAS committee (5.75 x 10-4 fatal 
cancers per rem, compared to the committee's figure of 5 x 
10-4 per rem). See 66 FR 32080-32081, for more discussion 
of health risks from ionizing radiation.
    \20\ For example, a 2007 NEA document on ``Consideration of 
Timescales in Post-Closure Safety of Geological Disposal of 
Radioactive Waste'' (NEA/RWMC/IGSC/(2006)3), which was based on 
surveys of Member Countries, points out that ``In evaluating 
compliance with regulatory criteria, or in formulating these 
criteria, extreme scenarios or parameter distributions can generally 
be assigned less weight. This is, for example, inherent in criteria 
expressed in terms of risk.'' (Docket No. EPA-HQ-OAR-2005-0083-0411, 
p. 38) Similarly, the UK Environment Agency has stated: ``In the 
1995 White Paper, the Government stated that reliance cannot be 
placed exclusively on estimates of risk to determine whether the 
facility is safe. Whilst such calculations can inform a judgement on 
the safety of the facility, other technical factors, including some 
of a more qualitative nature, will also need to be considered. The 
Government therefore considers it inappropriate to rely on a 
specified risk limit or risk constraint as an acceptance criterion 
for a disposal facility after control is withdrawn. It is, however, 
considered appropriate to apply a risk target in the design 
process.'' (Guidelines for Authorisation of Disposal Facilities for 
Low- and Intermediate-Level Radioactive Waste, Docket No. EPA-HQ-
OAR-2005-0083-0063, Paragraph 6.14)
---------------------------------------------------------------------------

    Risk correlations are highly dependent on population 
characteristics and baseline cancer rates, which change over time with 
dietary, lifestyle, medical, industrial, environmental, demographic, 
and other contributing factors. ICRP has expressed caution that 
``[d]oses and risks, as measures of health detriment, cannot be 
forecast with any certainty for periods beyond around several hundreds 
of years into the future * * * Such estimates must not be regarded as 
predictions of future health detriment.'' However, ICRP has also 
suggested that it is not unreasonable for shorter-term assessments to 
relate dose or risk to health effects: ``To evaluate the performance of 
waste disposal systems over long time scales, one approach is the 
consideration of quantitative estimates of dose or risk on the order of 
1000 to 10,000 years. This approach focuses on that period when the 
calculation of doses most directly relates to health detriment * * *'' 
(ICRP Publication 81, ``Radiation Protection Recommendations as Applied 
to the Disposal of Long-Lived Radioactive Waste,'' Docket No. EPA-HQ-
OAR-2005-0083-0417, Paragraphs 41 and 71, respectively) Thus, the 
Agency finds that its requirements for the probabilistic calculation of 
doses effectively incorporates the issue of risk as it has customarily 
been considered in long-term safety assessments. Further, the Agency 
believes its decision to view the 10,000-year standard within its 
traditional risk-management framework is reasonable and consistent with 
views on shorter-term safety assessments.
    The nominal annual risk level for fatal cancer associated with the 
100 mrem/yr dose standard is 5.75 x 10-5. This is comparable 
to the range of risks represented by national and international 
regulations identified by NAS for EPA to consider, and is premised on a 
dose level the NAS has addressed favorably as a matter of international 
regulatory consensus (NAS Report pp. 40-41, Tables 2-3 and 2-4). 
Considering that this standard will apply for up to 1 million years, we 
believe this represents a level of risk that will protect public health 
and safety in the far future. However, for the reasons described above, 
we do not believe it is appropriate to view the standard through a 
strict risk perspective, and caution against doing so. Further, even if 
the risk correlations could be assumed valid over such times, the 
nominal risk represented by projected doses may be a reflection of the 
uncertainties inherent in such projections, and therefore overstated. 
ICRP states, for example, that ``as the time frame increases, some 
allowance should be made for assessed dose or risk exceeding the dose 
or risk constraint * * * This must not be misinterpreted as a reduction 
in the protection of future generations, and, hence, as a contradiction 
of the principle of equity of protection, but rather as an adequate 
consideration of the uncertainties associated with the calculated 
results.'' (ICRP Publication 81, Docket No. EPA-HQ-OAR-2005-0083-0417, 
Paragraph 77).
    As a result of these considerations, for a standard covering 
periods up to 1 million years, the Agency believes it is more 
appropriate to view protectiveness from a broader perspective. This 
perspective must include consideration of the modeling issues discussed 
earlier, as well as be cognizant of the regulatory context in which 
dose projections will be presented. NRC's judgment of ``reasonable 
expectation'' will not rely on a simple comparison of the mean 
projected dose with the regulatory standard, but will encompass the 
data, assumptions, and models underlying those projections, including 
the sources and treatment of uncertainties and conservatisms. We are 
also mindful that the post-10,000-year peak dose standard

[[Page 61271]]

covers an extremely wide time window, far beyond that for any previous 
regulatory situation in this country, and that a peak mean dose could 
be projected to occur at any point within that time span. Where the 
precision and predictive capabilities of performance assessment models 
diminish over such long times, we believe it is appropriate that NRC 
``weigh how the scientific basis for analysis changes with time'' in 
reaching its judgment (NAS Report pp. 30-31).
    In that context, the 100 mrem/yr public dose limit recommended by 
ICRP and widely adopted by national and international organizations and 
government agencies represents a key element of radiation protection 
practice that can be applied to the estimation of potential future 
exposures. It provides a standard for public protection today and, by 
extension in the far future. This judgment reflects our view that the 
selected level must take into account larger, less quantifiable factors 
such as the uncertainties involved in projecting doses over 1 million 
years and the meaning that can be assigned to such projections (both in 
terms of their value as predictions of expected behavior of the 
disposal system and in their correlation with health effects), as well 
as the relative importance they should assume, in a regulatory context. 
Having considered these factors, we conclude that the post-10,000-year 
dose standard of 100 mrem/yr is protective of the RMEI. It must also be 
emphasized that the 100 mrem/yr level applies to the RMEI, who is 
described as a person whose location, lifestyle, and characteristics 
cause that person to be subject to doses at the high end of the local 
population. As a result, the RMEI is among the most highly exposed 
members of the public. Most residents in the vicinity of Yucca Mountain 
would receive much lower doses from the disposal system than the RMEI, 
if any dose at all.
    Taken together, the dual standards provide a reasonable test of the 
disposal system that appropriately combines protectiveness with 
recognition of the limitations of modeling in predicting the evolution 
of that system over hundreds of thousands of years. The 10,000-year 
standard is solidly grounded in the Agency's risk-management framework 
and prior practice for geologic disposal facilities. The longer-term 
peak dose standard is widely-accepted domestically and internationally 
as protective of public health and safety, reasonable in its 
recognition of the regulatory context, and fulfills our EnPA mandate by 
extending to the time of peak dose up to 1 million years. However, the 
Agency also emphasizes the site-specific nature of this rulemaking, 
which should not be viewed as a precedent for other regulatory 
situations, but as a reasoned response to unique circumstances 
involving issuance of a compliance standard applicable for periods up 
to 1 million years after disposal.
4. How Did We Consider Uncertainty and Reasonable Expectation?
    In establishing our final standards pursuant to the EnPA, we have 
considered two important statements from the NAS committee: (1) ``We 
recognize that there are significant uncertainties in the supporting 
calculations and that the uncertainties increase as the time at which 
peak risk occurs increases'' and (2) ``No analysis of compliance will 
ever constitute an absolute proof; the objective instead is a 
reasonable level of confidence in analyses that indicates whether 
limits established by the standard will be exceeded.'' (NAS Report pp. 
56 and 71, respectively) We have been mindful of these statements, as 
well as the fact that NAS deferred to our judgment in setting the level 
of the final compliance standard, as indicating that there are limits 
to the ability of science to provide definitive answers. ``When all 
reasonable steps have been taken to reduce technical uncertainty * * * 
there still remains a residual, unquantifiable uncertainty * * * The 
only defense against it is to rely on informed judgment.'' (NAS Report 
p. 80)
    We believe we have appropriately considered the NAS views in 
establishing 1 mSv/yr (100 mrem/yr) as the individual-protection 
standard for the period beyond 10,000 years and up to 1 million years. 
In order to approve DOE's license application, NRC must determine, at a 
minimum, that there is a reasonable expectation that standard will be 
met (as well as determine compliance with other NRC requirements, such 
as a multiple-barrier system). The primary indicator of compliance with 
the individual-protection standard is the mean of the distribution of 
projected doses presented by DOE (see Section III.A.9 of this document, 
``How Will NRC Determine Compliance?''). However, NRC's compliance 
determination will consist of more than a simple comparison of the mean 
of projected doses with the dose standard. Rather, as stated in 40 CFR 
197.14, NRC will reach its determination ``based upon the full record 
before it.'' Regardless of whether the mean of projected doses is well 
below the dose standard or not, NRC will examine the assumptions, data, 
models, and other aspects of DOE's projections to ensure that it has an 
understanding of those projections sufficient to reach a ``reasonable 
expectation'' as to their compliance with the standard (40 CFR 197.13). 
While applying the principles of reasonable expectation at all times, 
NRC may also use its judgment as to whether it would apply the concept 
in exactly the same way for times as long as 1 million years as it 
would for much shorter times. A key element of reasonable expectation 
is that it ``accounts for the inherently greater uncertainties in 
making long-term projections of the performance of the Yucca Mountain 
disposal system'' (Sec.  197.14(b)), we would consider it logical as 
well as practical for NRC, in reaching its compliance decision, to 
evaluate the sources and effects of uncertainties in DOE's analyses, as 
well as DOE's treatment of them.\21\
---------------------------------------------------------------------------

    \21\ ICRP Publication 81: ``Demonstration of compliance with the 
radiological criteria is not as simple as a straightforward 
comparison of calculated dose or risk with the constraints, but 
requires a certain latitude of judgement.'' (Docket No. EPA-HQ-OAR-
2005-0083-0417, Paragraph 86)
---------------------------------------------------------------------------

    Uncertainties can influence performance assessments in a number of 
ways. Some sources of uncertainty can be addressed, or at least 
accounted for, while in other areas our knowledge may be too limited to 
even characterize the uncertainty, much less explicitly account for it. 
Sources of uncertainty are often discussed in broad categories such as 
``data'' or ``model'' uncertainty, although these can take on various 
forms within those broader categories that create individual 
challenges.\22\
---------------------------------------------------------------------------

    \22\ For example, ``data'' uncertainty can cover broad issues 
such as whether sufficient data are available, whether the right 
kind of data are available, whether the data are of sufficient 
quality, and whether the available data adequately capture what NAS 
referred to as ``the difficulties in spatial interpolation of site 
characteristics'' which ``will be present at all times'' (NAS Report 
p. 72). Similarly, ``model'' uncertainty includes not only whether 
the processes acting on the site have been correctly represented 
mathematically and coupled with each other, but also whether the 
basic understanding of which processes operate, whether there are 
competing mechanisms that must be considered (e.g., for corrosion or 
ground-water flow), and the extent to which and conditions under 
which one mechanism is dominant.
---------------------------------------------------------------------------

    NAS supported the use of probabilistic modeling as one way to 
address the effects of uncertainty. However, NAS noted that this 
process itself can involve significant uncertainties in defining the 
parameter value distributions from which the probabilistic selections 
would be made. (NAS Report pp. 78-79) As a result, interpretation of 
probabilistic results, which illustrate uncertainty through the 
distribution of calculated values, may

[[Page 61272]]

also be affected by this underlying uncertainty, which may not be fully 
appreciated or understood.
    Selecting an appropriate dose limit for periods up to 1 million 
years must also consider the ability of performance assessments, and 
those who interpret them, to distinguish between differing repository 
designs, as well as different conceptualizations of total system 
performance over very long time frames. We have described the general 
view that the predictive capabilities of performance assessments 
diminish as the time periods covered by the assessments increase. It is 
also important to understand that, while mathematical calculations can 
result in very precise estimates of dose (to multiple significant 
digits), this precision is misleading in its presentation of the 
approximate outcomes of multiple interacting processes. We believe it 
is not appropriate to imply that there is a clear and immutable 
difference between two projections of dose, when it is understood that 
neither on its own is an unqualified representation of reality. Such 
representations may promise more than can be delivered by the model's 
ability to ``slice it thin.'' \23\ In our view, it makes little sense 
to assert that a 15 mrem/yr dose limit for the period within 10,000 
years is more ``protective'' than a higher limit much later in time if, 
in the time frame of hundreds of thousands of years, the uncertainties 
in projecting disposal system performance cannot easily make 
distinctions at such incremental levels.\24\
---------------------------------------------------------------------------

    \23\ This problem is not specific to quantitative performance 
assessment. Similar issues have been identified in analysis of 
different policy options for energy or other areas associated with 
technological risk. It has been noted that ``The results of 
individual risk assessment studies are often reported with 
formidable precision, expressed as discrete numbers (rather than 
ranges) and presented to two, three and even four significant 
figures. Yet * * * such precision seems entirely to misrepresent the 
accuracy of this style of appraisal taken as a whole * * * the 
problem does not tend to be driven by any single factor in analysis, 
nor is it a simple matter of some studies being more `accurate' or 
`reasonable' than others in any definitive sense. The manifest 
variability * * * is rather a simple reflection of * * * the 
adoption of different (but equally scientifically valid) assumptions 
and priorities concerning the multitude of different dimensions of 
risk. Where [different options cannot be clearly distinguished] in 
any absolute sense, then the value of appraisal lies in exposing the 
relationships between different assumptions in analysis and the 
associate pictures of the relative importance of different options. 
It is better to be roughly accurate in this task of mapping the 
social and methodological context-dependencies than it is to be 
precisely wrong in spurious aspirations to a one-dimensional 
quantitative expression of technological risk.'' (``On Science and 
Precaution in the Management of Technological Risk,'' Volume 1, 
Institute for Prospective Technical Studies, 1999, Docket No. EPA-
HQ-OAR-2005-0083-0413, pp 13-16, emphasis in original)
    \24\ One might compare this situation to finding two proximate, 
but distinct, locations on a road map. In the first instance, the 
scale on the map is such that all individual roads and landmarks 
(e.g., schools, churches, libraries) can be seen. One can easily 
locate each site and circle it. Now consider a map of the same size, 
in which the scale is much smaller, showing only major thoroughfares 
and main local roads. One would still be able to approximate the 
desired location(s), but any attempt to circle them would likely 
encompass both (and may be deliberately larger to ensure that both 
are captured). Thus, the ability to distinguish the two locations 
hinges on the scale and detail of the map in question. The change in 
``scale'' for our rulemaking is the extension of the compliance 
period to 1 million years.
---------------------------------------------------------------------------

    In responding to comments on this issue, we considered how it might 
be possible to demonstrate the increase in projected uncertainties and 
provide a quantitative estimate of the degree of increased uncertainty 
that might be encountered as a result of variation in parameter values. 
To examine the long-term propagation of uncertainty in dose 
projections, we used a simplified Yucca Mountain site performance 
assessment model and constructed a hypothetical disposal system that 
would produce a mean dose to the RMEI of 15 mrem/yr at 10,000 years. 
That is, we estimated the number of waste package failures that would 
be necessary to produce a disposal system operating at the ``edge of 
compliance'' at 10,000 years. This disposal system, which would still 
meet the performance standard at 10,000 years, was the reference base 
case for our uncertainty analyses. The number of ``failed'' waste 
packages needed to produce the reference case dose (a mean of 15 mrem/
yr at 10,000 years) was calculated using the simplified site model and 
parameters used in the DOE model, and assumed some components of the 
engineered barrier did not function to provide containment (i.e., the 
titanium drip shields designed to divert water from the waste packages, 
as well as other components of the engineered barrier system, were 
removed from the model).\25\ Further, upon ``failure'' of a waste 
package, the entire inventory of that package was assumed to be 
available for dissolution and transport, subject to solubility limits 
applied to each radionuclide.
    To assess the progressive effects of uncertainty, the number of 
``failed'' packages was limited to the number necessary to produce 15 
mrem/yr at 10,000 years, and the hypothetical site model was used to 
make dose projections from 10,000 years (the reference base case) 
through the period of peak dose within the period of geologic 
stability. Thus, the system established as a starting point for the 
peak dose projections was one in which some degree of release and 
transport to the RMEI had already taken place within the initial 10,000 
years, providing a basis for judging how the continuation of these 
processes would change the results over time. These analyses examined 
the effects of uncertainties from the natural barrier portion of the 
disposal system, since additional waste package failures were not 
considered.\26\ It should be recognized that the base case was 
determined using probabilistic methods, so the results at 10,000 years 
already showed some effects of uncertainty, as indicated by the range 
of projected doses with the mean at 15 mrem/yr.
---------------------------------------------------------------------------

    \25\ Although it employed site parameter value distributions 
used by DOE, the model used in this analysis was simplified and 
``forced'' to the boundary condition of a 15 mrem/yr mean dose at 
10,000 years. This analysis should in no way be compared to the 
modeling conducted to support DOE's license application.
    \26\ We considered release of radionuclides from the waste form 
as a natural process dependent on solubility parameters. The waste 
form itself (spent fuel assemblies or vitrified HLW) is often 
considered part of the engineered barrier system.
---------------------------------------------------------------------------

    We found that the uncertainty in dose projections, from the base 
case (at 10,000 years) to peak dose (as measured by the spread in dose 
estimates between the 5th and 95th percentiles at these times), 
increased by approximately two orders of magnitude. These results 
showed quantitatively that uncertainty in performance projections does 
increase with time for the Yucca Mountain system, and supports the 
premise that increasing uncertainty reduces the degree of confidence 
that can be assumed for very long-term performance assessments. We 
believe this supports the premise, discussed earlier, that increasing 
uncertainty in dose projections over very long time periods lessens the 
ability of performance assessment modeling to meaningfully distinguish 
among alternative (and equally ``likely'') ``futures'' represented by 
individual model simulations, and ultimately to distinguish among 
alternate models and assumptions for site performance assessments. More 
detail on the site model we used, parameter databases, sensitivity 
analyses and discussion of the results, is provided in the technical 
reports describing this work (Docket No. EPA-HQ-OAR-2005-0083-0386).
    NRC must reach a determination of compliance based on the specific 
case presented by DOE. In order to conclude that there is a reasonable 
expectation that the Yucca Mountain disposal system will comply with 
our standard of 100 mrem/yr, NRC must understand the technical basis 
for DOE's projections,

[[Page 61273]]

including the inherent uncertainties. We believe it is appropriate for 
NRC to examine uncertainty in its licensing review in order to achieve 
the necessary level of confidence in DOE's understanding and depiction 
of the disposal system. Ultimately, in reaching its compliance 
determination, it is incumbent upon NRC to clearly state what it can or 
cannot conclude from the performance assessment results, within the 
limits of science.
5. How Did We Consider Background Radiation In Developing the Peak Dose 
Standard?
    We are not adopting the proposed 3.5 mSv/yr (350 mrem/yr) level as 
the compliance standard for the period beyond 10,000 years, nor have we 
adopted the reasoning used to support the proposed standard (i.e., 
considerations of specific background radiation estimates) to the 
selection of the 100 mrem/yr level. We received significant comment on 
this aspect of our proposal, much of it taking issue with the concept 
of using background radiation as an indicator of ``safe'' levels of 
exposure from an engineered facility. We also received additional 
information that provided insights into and refined our consideration 
of background radiation. For example, commenters referred to monitoring 
data collected by the Desert Research Institute indicating that the 
unshielded (outdoor) background radiation from cosmic and terrestrial 
sources in Amargosa Valley is roughly 110 mrem/yr. Commenters also 
informed us that roughly 90% of the population in Amargosa Valley lives 
in mobile homes, which has implications for indoor radon exposures. 
Other commenters supported the use of a different factor for converting 
radon concentrations into dose.
    In considering these comments, as well as those taking issue with 
the overall premise described in the proposal, we found the relatively 
simple approach used in the proposal evolving into a more complex 
undertaking requiring numerous decisions where science did not provide 
a definitive answer. Addressing indoor radon estimates presented the 
greatest challenge, as indoor radon represented the highest proportion 
of overall background radiation. Complicating factors included multiple 
ways of calculating radon dose, the prevalence of mobile homes in 
Amargosa Valley, limited data sets primarily from the early 1990s, and 
data for individual counties in a different format than state-wide 
data. We concluded that there was no generally agreed-upon approach in 
the context of Amargosa Valley for incorporating indoor radon exposures 
into an analysis of background radiation that would lead to a 
regulatory standard, particularly given the fact that many commenters 
viewed the entire concept as arbitrary. Accordingly, we have decided 
not to adopt a standard derived from an analysis of background 
radiation estimates at specific locations or the differences between 
background radiation estimates at different locations.
    We continue to believe that references to natural sources of 
radiation can provide useful insights. IAEA has observed that ``[i]n 
very long time frames * * * uncertainties could become much larger and 
calculated doses may exceed the dose constraint. Comparison of the 
doses with doses from naturally occurring radionuclides may provide a 
useful indication of the significance of such cases''. (IAEA WS-R-4, 
Docket No. EPA-HQ-OAR-2005-0083-0383, Paragraph A.8) We note that the 
100 mrem/yr level reasonably comports with such an analysis as well. 
For example, as noted above, 100 mrem/yr is roughly the value reported 
by the Desert Research Institute for cosmic and terrestrial radiation 
at Amargosa Valley (unshielded). When shielding from buildings is 
considered and indoor radon doses are estimated using a more 
conservative conversion factor suggested by some commenters, 100 mrem/
yr is at the low end of overall background radiation estimates in 
Amargosa Valley and nationally. Within the State of Nevada, the 
difference in average estimates of background radiation for counties is 
greater than 100 mrem/yr. (Docket No. EPA-HQ-OAR-2005-0083-0387) As 
previously stated, this suggests that 100 mrem/yr can be considered to 
be a level such that the total potential doses incurred by the RMEI 
from the combination of background radiation and releases from Yucca 
Mountain will remain below doses incurred by residents of other parts 
of the country from natural sources alone.\27\ It may also be noted 
that the 100 mrem/yr public dose limit recommended by ICRP is itself 
related to background radiation, so indirectly our peak dose standard 
does incorporate the concept of variations in background radiation.\28\ 
However, in the absence of compelling reasons for selecting specific 
background radiation estimates and points of comparison, we conclude 
that comparing background radiation estimates from specific locations 
does not provide a clear or sufficient basis for a regulatory 
compliance standard applicable to the Yucca Mountain disposal system. 
Discussion of specific issues raised in public comments is in Section 3 
of the Response to Comments document.
---------------------------------------------------------------------------

    \27\ It could also be considered consistent with the NEA 
statement that ``[w]hat can be aimed at, however, is to leave future 
generations an environment that is protected to a degree acceptable 
to our own generation. It is also relevant to observe that this 
level of protection will ensure that any radiological impacts due to 
disposal will not raise levels of radiation above the range that 
typically occurs naturally.'' (``The Handling of Timescales in 
Assessing Post-Closure Safety: Lessons Learnt from the April 2002 
Workshop in Paris, France,'' p. 9, Docket No. EPA-HQ-OAR-2005-0083-
0046)
    \28\ ``This natural background may not be harmless * * * but the 
variations from place to place (excluding the large variations in 
the dose from radon in dwellings) can hardly be called unacceptable 
* * * Excluding the very variable exposures to radon, the annual 
effective dose from natural sources is about 1 mSv, with values at 
high altitudes above sea level and in some geological areas of at 
least twice this. On the basis of all these considerations, the 
Commission recommends an annual limit on effective dose of 1 mSv.'' 
(ICRP Publication 60, Docket No. EPA-HQ-OAR-2005-0083-0421, 
Paragraphs 190-191)
---------------------------------------------------------------------------

6. How Does Our Rule Protect Future Generations?
    Because of its long lifetime, high hazard, and potential for 
misuse, SNF and HLW present special challenges to those charged with 
protecting the health, safety, and security of the public and the 
environment. Geologic disposal has long been viewed by policymakers as 
the management option that best addresses all of these concerns.\29\ In 
the United States, geologic disposal was first endorsed by the NAS in 
1957 (``The Disposal of Radioactive Waste on Land'') and established as 
national policy in the Nuclear Waste Policy Act of 1982.
---------------------------------------------------------------------------

    \29\ In its 1995 Collective Opinion, the NEA Radioactive Waste 
Management Committee concludes that ``from an ethical standpoint, 
including long-term safety considerations, our responsibilities to 
future generations are better discharged by a strategy of final 
disposal than by reliance on stores which require surveillance, 
bequeath long-term responsibilities of care, and may in due course 
be neglected by future societies whose structural stability should 
not be presumed'' and ``after consideration of the options for 
achieving the required degree of isolation of such wastes from the 
biosphere, geological disposal is currently the most favoured 
strategy,'' whereby ``it is justified, both environmentally and 
ethically, to continue development of geological repositories for 
those long-lived radioactive wastes which should be isolated from 
the biosphere for more than a few hundred years.'' (``The 
Environmental and Ethical Basis of Geological Disposal of Long-Lived 
Radioactive Wastes,'' Docket No. EPA-HQ-OAR-2005-0083-0412, pp. 5-6) 
Similarly, the NAS Board on Radioactive Waste Management stated: 
``There is a strong worldwide consensus that the best, safest long-
term option for dealing with HLW is geological isolation.'' 
(``Rethinking High-Level Radioactive Waste Disposal: A Position 
Statement of the Board on Radioactive Waste Management,'' 1990, 
Docket No. EPA-HQ-OAR-2005-0083-0420, p. 2)
---------------------------------------------------------------------------

    However, the fact that geologic disposal has potentially 
significant

[[Page 61274]]

impacts over times far in excess of recorded human history naturally 
raises concerns as to how the welfare of people living far in the 
future can and should be taken into account when societal institutions 
may no longer exist to provide oversight of a disposal facility.\30\
---------------------------------------------------------------------------

    \30\ NEA states: ``The design and implementation of a repository 
involves balancing of risks and responsibilities between 
generations. The obligations of the present generation toward the 
future are complex, involving not only issues of safety and 
protection but also of freedom of choice and of the accompanying 
burden of responsibility, and of the need to transfer knowledge and 
resources. Our capacity to deliver these obligations diminishes with 
distance in time, which complicates the setting of criteria to be 
used today in order to demonstrate that obligations to the future 
will be met.'' NEA-6182, Docket No. EPA-HQ-OAR-2005-0083-0408, p. 
25)
---------------------------------------------------------------------------

    In considering how our standards reflect these intergenerational 
issues, we considered the guidance offered by the NAS committee. (See 
70 FR 49036) In citing NRC and IAEA sources on the question of 
intergenerational equity, NAS wrote:

    A health-based risk standard could be specified to apply 
uniformly over time and generations. Such an approach would be 
consistent with the principle of intergenerational equity that 
requires that the risks to future generations be no greater than the 
risks that would be accepted today. Whether to adopt this or some 
other expression of the principle of intergenerational equity is a 
matter for social judgment.

NAS Report pp. 56-57, emphasis added.

    We generally agree with the NAS statement. A single dose standard 
applicable at all times would typically be consistent with a close 
reading of the principle of intergenerational equity as stated by NAS. 
However, NAS clearly acknowledges that ``some other'' approach could 
also be consistent with that principle. We believe it is reasonable to 
conclude that ``some other'' approach must include situations where it 
may not be reasonable to apply the same dose standard at all times 
because of the extremely long compliance period. We believe 
establishing a peak dose standard for the Yucca Mountain disposal 
system is a situation in which ``some other expression of 
intergenerational equity'' is more appropriate than is applying a 
single dose standard of 15 mrem/yr throughout the compliance period. 
The rulemaking process we are following is the accepted way for 
``social judgment'' to be incorporated into regulations.
    NAS made no recommendation regarding the appropriate expression of 
intergenerational equity, just as it made no recommendation regarding 
the level of the final peak compliance standard. Rather, NAS 
acknowledged EPA's wide latitude to exercise its policy judgment.
    We emphasize that we do not question whether there is an obligation 
to future generations, but we believe there is no consensus regarding 
the nature of that obligation, for how long it applies, whether it 
changes over time, or how it can be discharged. Regarding radioactive 
waste management and geologic disposal, there is general agreement that 
assurances can be provided that the protections offered will be similar 
to those applied to current activities for periods approximating 10,000 
years, which is a very long time. It also is generally accepted that 
engineered barriers cannot be relied upon indefinitely, and that 
projected doses may eventually exceed the initial regulatory levels. 
The question of equity is also raised by the fact that the repository 
is part of a passive disposal system that may provide complete 
containment for hundreds of generations without their knowledge, but 
present the greatest risks to equally unsuspecting generations beyond 
that time. However, it is unclear as to exactly how such long-term 
projected doses should be factored into a judgment of facility safety, 
if we are not confident they can be interpreted in the same way at all 
times.\31\ We are establishing today a standard consistent with a 
public dose limit of 100 mrem/yr that is deemed protective today as a 
matter of international consensus, which would not affect the quality 
of life for future generations, even those hundreds of thousands of 
years distant. We believe this is a reasonable level of commitment for 
such long times, given the complexities of the situation and what we 
see as our responsibility to establish a level of compliance, not a 
soft target or reference level that could be exceeded for unspecified 
reasons and by unspecified amounts.
---------------------------------------------------------------------------

    \31\ NEA-6182: ``National programmes which have already 
established such criteria have generally found it possible to make 
cautious, but reasonable assumptions to extend the use of 
radiological limits already applied to contemporary activities for 
several thousands of years. The greater challenge lies in setting 
criteria for very long time frames, extending to a million years and 
beyond, for which safety analyses must account for high uncertainty 
and for which the understanding of the needs and impacts on future 
generations become increasingly speculative.'' (Docket No. EPA-HQ-
OAR-2005-0083-0408, pp. 20-21).
---------------------------------------------------------------------------

    In conclusion, EPA acknowledges and remains committed to the 
principles of intergenerational equity. However, we do not interpret 
these principles as requiring that the same compliance standard must 
apply at all times. Such an approach is overly simplistic in the 
circumstances and ignores the complexities involved in establishing 
radiological protection standards for periods approaching 1 million 
years. We believe that peak dose limits over such periods should be 
viewed as qualitatively different from limits applied at earlier times; 
in other words, the basis for judgment at different times is not the 
same. As a matter of public policy, a commitment to protect future 
generations over the next 10,000 years at levels consistent with 
standards applied for the current generation, and to protect more 
distant generations at levels consistent with the overall public dose 
limits deemed protective today and adopted nationally and 
internationally, protects public health and the environment across 
generations in a manner that comports with the objective of 
intergenerational equity. Under this approach, future generations will 
not face undue burdens or the irreversible loss of reasonable options 
arising from a decision by the current generation to pursue a policy of 
geologic disposal at Yucca Mountain, nor will the compliance 
demonstration demand more than can be provided by scientific analysis. 
The standards applicable to both time frames are protective of public 
health and safety and will offer comparable, if not identical, 
protections to the affected generations. See section 9 of the Response 
to Comments document for more detailed discussion of these issues.
7. What is Geologic Stability and Why is it Important?
    Underlying the NAS recommendation to assess compliance at the time 
of maximum risk is the concept of geologic stability (i.e., peak dose 
should be assessed ``within the limits imposed by the long-term 
stability of the geologic environment,'' NAS Report p. 2). NAS viewed 
this as an important consideration in assessing performance, both 
analytically and in regulatory review. Indeed, NAS discussed two 
important kinds of uncertainty in describing this concept, which are 
spatial and temporal uncertainty. The committee concluded that spatial 
uncertainties will always exist no matter what time frame is used for 
the performance assessments. Temporal uncertainties, on the other hand, 
will vary over different time frames, and the presence of such 
uncertainties indicates the advisability of defining a ``period of 
geologic stability,'' during which performance projections can be made 
with some degree of confidence. For time periods where conditions at 
the site would change dramatically in a relatively short time, 
projections of site

[[Page 61275]]

conditions would be highly speculative, and consequently performance 
assessments would have very limited if any validity. It is important to 
understand that ``stable'' in this context is not synonymous with 
``static and unchanging.'' Rather, NAS recognized that many ``physical 
and geologic processes'' are characteristic of any site and have the 
potential to affect performance of the disposal system. NAS concluded 
that these processes could be evaluated as long as ``the geologic 
system is relatively stable and varies in a boundable manner'' (NAS 
Report p. 9). Thus, the site itself could be anticipated to change over 
time, but in relatively narrow ways that can be defined (``bounded''). 
Implicit in the NAS recommendation is the idea that the maximum risk 
might occur outside the period of geologic stability, but assessments 
performed at that time would have little credibility and would not be a 
legitimate basis for regulatory decisions: ``After the geologic 
environment has changed, of course, the scientific basis for 
performance assessment is substantially eroded and little useful 
information can be developed.'' (NAS Report p. 72)
    NAS judged this period of ``long-term stability'' to be ``on the 
order of one million years.'' (NAS Report p. 2) We describe in section 
III.A.8 (``Why is the Period of Geologic Stability 1 Million Years?'') 
the policy judgment on our part to explicitly equate the period of 
geologic stability with 1 million years. More important, however, is to 
understand the relationship among the regulatory definition, the 
physical reality of the site, and the performance assessment models. In 
reaching its conclusion, NAS considered information available on the 
site properties and the processes as they currently operate. This 
provides a basis for understanding how the site functions today, but 
would not be sufficient to project that understanding for periods of 
millions of years into the future. To do that, NAS also considered 
information obtained through studies of the geologic record at the 
site, to see if evidence existed for times when processes were either 
fundamentally different or they operated at different rates. This is 
similar to our recommendation that DOE consider at least the last two 
million years (the Quaternary period) in characterizing FEPs. In fact, 
examination of the Quaternary geologic record is an important component 
in understanding the evolution of the geologic setting over time. NAS 
expressed confidence that neither the processes active at the site, nor 
the site itself, had changed in fundamental ways over the Quaternary 
Period and longer, and probably would continue to behave much as it 
does today for the next million years. NAS therefore suggested that 
geologic conditions could be bounded with reasonable confidence for 
periods ``on the order of one million years.'' (NAS Report p. 2)
    Models used to assess performance need to incorporate a description 
of the bounds under which the model can be considered valid, so as to 
avoid physically impossible situations, as well as assure that the 
conceptual models upon which the performance assessments are based 
reasonably represent the way the site is expected to behave over the 
period of stability. They must be defined so that significant changes 
to the properties of the site and physical and geologic processes are 
not projected inadvertently to create conditions of ``geologic 
instability.'' That is, they must avoid crossing over into sets of 
conditions that would in reality not be a geologically stable 
situation, or are outside the bounds under which the model can be 
considered valid. Here again the examination of the geologic record at 
the site provides the means of constructing the models to adequately 
make simulations of future performance that reflect the range of 
potential expected conditions at the site over the regulatory 
compliance period. Parameter value distributions used in the 
simulations, which are the fundamental input information used to make 
the dose assessments, should not be limited only to data collected for 
the present situation at the site, but should consider how those 
parameter values could change over the period of stability. Expert 
judgment, where appropriate, based upon site-specific information and 
broader understanding of how these processes operate in general, plays 
an important role in defining such modeling input data.
    The geologic record is the primary source of information on the 
question of geologic stability and was considered by NAS in reaching 
its conclusions about the geologic stability period. We believe that 
the geologic record at the site clearly supports the position that the 
site will be stable over the course of the next million years. 
Conclusions based on extrapolation beyond what can be supported in the 
geologic record should be avoided.
8. Why is the Period of Geologic Stability 1 Million Years?
    Today's final rule includes a compliance period of 1 million years, 
over which DOE must project performance and demonstrate compliance with 
the individual-protection and human-intrusion standards. As discussed 
at length in our proposal and more briefly in Sections I and II of this 
document, our rulemaking is in response to the DC Circuit decision 
vacating the 10,000-year compliance period in our 2001 rule. The Court 
concluded that the 10,000-year compliance period was not based upon and 
consistent with the NAS recommendations, as the EnPA required. NAS 
recommended ``that compliance with the standard be assessed at the time 
of peak risk, whenever it occurs, within the limits imposed by the 
long-term stability of the geologic environment, which is on the order 
of one million years.'' (NAS Report p. 2) NAS found that ``compliance 
assessment is feasible for most physical and geologic aspects of 
repository performance on the time scale of the long-term stability of 
the fundamental geologic regime,'' and accordingly ``there is no 
scientific basis for limiting the time period of an individual-risk 
standard.'' (NAS Report p. 6) As a matter of policy, we believe it is 
appropriate and necessary to define a compliance period within which 
our standards apply. This section discusses the considerations that led 
us to conclude that a compliance period of 1 million years is 
appropriate from a policy perspective and consistent with NAS 
statements regarding geologic stability at Yucca Mountain.
    As discussed in section III.A.7 (``What is Geologic Stability and 
Why is it Important?''), the NAS introduced the concept of geologic 
stability in its report and referred to it repeatedly in its 
discussions (NAS Report, e.g., pp. 9, 55, 69, 71, and 72). In 
discussing the physical properties and geologic processes leading to 
the transport of radionuclides away from the repository, the NAS 
committee concluded ``that these physical and geologic processes are 
sufficiently quantifiable and the related uncertainties sufficiently 
boundable that the performance can be assessed over time frames during 
which the geologic system is relatively stable or varies in a boundable 
manner.'' (NAS Report p. 9) While variation of site characteristics 
over time produces some uncertainty, NAS believed that such changes 
could be bounded during the period of geologic stability of the site, 
i.e., as long as the conditions do not change significantly. (NAS 
Report pp. 72, 77) NAS also noted that ``[a]fter the geologic 
environment has changed, of course, the scientific basis for

[[Page 61276]]

performance assessment is substantially eroded and little useful 
information can be developed.'' (NAS Report p. 72) While NAS made no 
additional qualification on what constituted ``significant'' changes, 
it made numerous references in its report to a stability period for the 
site ``on the order of one million years.'' The committee concluded 
that during this period it would be feasible to make projections of 
repository site conditions. We concur and believe that assessments can 
be made and bounded where uncertainty exists, and consequently 
performance assessments can be developed with adequate confidence for 
regulatory decision-making within the context of the requirements 
adopted in today's final rule. We discuss some additional 
qualifications to this proposition in the remainder of this section.
    While the NAS characterized the length of the geologic stability 
period in loose terms (``on the order of''), we believe it is 
appropriate to fix the stability period duration as a matter of 
regulatory policy. We find support on this point from NAS: ``It is 
important, therefore, that the `rules' for the compliance assessment be 
established in advance of the licensing process.'' (NAS Report p. 73). 
We believe, therefore, as a matter of regulatory philosophy and policy, 
that a relatively loosely defined stability period ``on the order of'' 
one million years is not sufficiently specific for regulatory purposes, 
i.e., implementing our standards and reaching a compliance decision. 
Indeed, NAS clearly considered that the compliance period could be one 
of the ``rules'' that should be established for compliance assessments. 
(NAS Report p. 56) Some commenters suggested that the period of 
geologic stability could be longer (or interpreted ``on the order of 
one million years'' as possibly as long as ten million years), and said 
our rule should allow consideration of longer timescales if justified 
by considerations of geologic stability. The actual period of geologic 
stability at Yucca Mountain is unknowable, and we disagree that an 
open-ended compliance standard is justified over such time frames. We 
believe that the applicant (DOE) and the compliance decision-maker 
(NRC) must have definitive markers to judge when compliance is 
demonstrated, and that a loosely defined time frame does not provide 
such a marker for implementation of our standards in a licensing 
process. We believe that the geologic stability period of 1 million 
years that we have defined provides the necessary marker, and is within 
our discretion to set as a matter of policy. (See generally NAS Report 
p. 3) To do otherwise we believe would leave the licensing process in a 
potentially untenable situation of dealing with possibly endless debate 
over exactly when a peak dose occurs in relation to a compliance period 
time limit. Such debate can arise because of the inherent uncertainty 
that exists in characterizing the complex processes and variables 
involved in projecting performance of the disposal system over very 
long periods of time. As the NAS explained, ``although the selection of 
a time period of applicability has scientific elements, it also has 
policy aspects we have not addressed.'' (NAS Report p. 56)
    As commenters have pointed out, the rate of waste package failure 
is a dominant factor in determining when the peak dose for a 
probabilistic assessment will occur. With all the parameters (and the 
uncertainty in their values over time) involved in a total system 
performance assessment, as well as the assumptions necessary to select 
processes involved in projecting performance, it is quite possible that 
significant debate could result in the licensing process over selection 
of the parameter values and the resulting timing of the peak dose 
results. We do not believe such debate is constructive because it would 
not advance the goal of providing a reasonable test of the disposal 
system. We also believe that the 1 million year stability period 
provides the needed definitive marker for judging the time over which 
the standards apply and is an appropriate exercise of our policy 
discretion.
    Throughout our proposal and in this final rule we have cited a 
significant number of international references to support policy 
judgments such as the one discussed here. Readers may recall that we 
cited such references suggesting that dose projections beyond 1 million 
years have little credibility and believe that we used those arguments 
to justify proposing the 1 million-year compliance period (70 FR 49036, 
August 22, 2005). We did not explicitly discuss in the proposal our 
reasons for selecting 1 million years as the compliance period and 
equating it to the period of geologic stability, other than references 
to the NAS language that it is ``on the order of'' 1 million years. 
However, these sources do generally reflect widespread acceptance of 
the proposition that quantitative performance projections at very long 
time frames have limited utility for regulatory decision-making, and 
that 1 million years may be a reasonable reference point beyond which 
such projections either should not be required or should be considered 
only in their broadest sense.\32\ Further, while it should be clear 
that we agree with the thrust of those international sources regarding 
the effects of uncertainty on long-term dose projections and the 
relative level of confidence that can be placed in them for decision-
making, we believe the post-10,000-year peak dose standard in today's 
final rule appropriately accommodates those considerations and is 
protective of public health, meaningful, implementable, and provides a 
reasonable test of the disposal system that is consistent with the NAS 
Report, DC Circuit decision, and the principles of reasonable 
expectation.
---------------------------------------------------------------------------

    \32\ For example, in general guidance documents, the IAEA has 
stated that ``little credibility can be attached to assessments 
beyond 10\6\ years.'' (``Safety Indicators in Different Time Frames 
for the Safety Assessment of Underground Radioactive Waste 
Repositories,'' IAEA-TECDOC-767, p. 19, 1994, Docket No. EPA-HQ-OAR-
2005-0083-0044) In its final 2006 Safety Requirements for Geological 
Disposal of Radioactive Waste, IAEA also states, ``Care needs to be 
exercised in using the criteria beyond the time where the 
uncertainties become so large that the criteria may no longer serve 
as a reasonable basis for decision making.'' (Docket No. EPA-HQ-OAR-
2005-0083-0383, page 11, paragraph 2.12) As a country-specific 
example, final guidelines from the Swedish Radiation Protection 
Authority state that ``the risk analysis should be extended in time 
as long as it provides important information about the possibility 
of improving the protective capability of the repository, although 
at the longest for a time period of one million years.'' (Docket No. 
EPA-HQ-OAR-2005-0083-0388) Also, in an example where the official 
guidelines specify a risk target that is of undefined duration, the 
United Kingdom's National Radiological Protection Board has stated 
that ``[o]ne million years is * * * the timescale over which stable 
geological formations can be expected to remain relatively 
unchanged,'' while concluding that the scientific basis for risk 
calculations past one million years is ``highly questionable.'' 
(``Board Statement on Radiological Protection Objectives for the 
Land-based Disposal of Solid Radioactive Wastes,'' 1992 Documents of 
the NRPB, Volume 3, No. 3, p. 15, Docket No. EPA-HQ-OAR-2005-0083-
0416)
---------------------------------------------------------------------------

    To support these general policy arguments, which would lead us to 
consider a time period of approximately 1 million years as an 
appropriate regulatory time frame, it is necessary to address NAS's 
scientific judgments. While NAS did not define with precision the 
period of time that the geologic environment likely would remain 
stable, for purposes of our regulation we believe scientific 
information can be relied upon to support a firm definition of that 
period as ending at 1 million years after disposal. Further, we believe 
that equating a specific time period with the ``period of geologic 
stability'' is a site-specific decision, as NAS's statements regarding 
geologic stability were wholly in the context of Yucca Mountain. (See, 
for example, NAS Report p. 69: ``The time scales of long term geologic

[[Page 61277]]

processes at Yucca Mountain are on the order of 10\6\ years''; and NAS 
Report p. 85: ``The geologic record suggests this time frame is on the 
order of about 10\6\ years.'') Therefore, we have considered how the 
natural processes and characteristics at the Yucca Mountain site would 
support defining the period of geologic stability as ending at a 
specified time after disposal. In considering the natural setting, many 
comments expressed the view that the site's natural characteristics are 
so conducive to rapid release and transport of radionuclides, only the 
waste packages and other engineered barriers would make it possible for 
significant doses to be delayed much beyond 10,000 years. We believe it 
is therefore also appropriate to consider the geologic stability period 
from the perspective of a reasonable length of time for significant 
events to act on the waste packages and engineered barriers, and 
ultimately lead to release of radionuclides. Natural processes and 
events would contribute to both the package failures and to the 
subsequent transport of radionuclides, even if such failures occur 
relatively late in the period under consideration.
    A consideration of the geologic history of the site, in the areas 
of igneous and seismic activity, also supports a 1 million year 
stability period. Information compiled by NRC (Docket No. EPA-HQ-OAR-
2005-0083-0373) concerning basaltic igneous activity around the site 
shows that this type of activity has been the only activity around the 
site through the Pliocene (beginning roughly 5.4 million years ago), 
and that the volume of eruptive activity (both tuff and basaltic 
material) has decreased continually over the last 10 million years 
(Coleman et al., 2004, Docket No. EPA-HQ-OAR-2005-0083-0378). From the 
identification of surface features as well as indicators of buried 
remnants of past volcanic activity, the episodes of basaltic activity 
around the site can be shown to have occurred in clusters of events 
around 1 million and 4 million years ago (Hill, 2004, Docket No. EPA-
HQ-OAR-2005-0083-0373). The occurrence of these clusters indicates that 
the nature and extent of past volcanic activity can be reasonably well 
characterized and that annual probabilities for such events can be 
reasonably estimated from the geologic record around the site. Annual 
probabilities of volcanic disruptions to the repository have been 
estimated by various investigators, and range from as high as 
10-6 to as low as 5.4 x 10-10 (Coleman et al., 
2004, Docket No. EPA-HQ-OAR-2005-0083-0378).
    Further, while geologic stability may be viewed as being affected 
primarily by large-scale events, accumulations of small-scale changes 
over very long time periods also have the potential to alter the 
geologic setting and affect the technical basis for performance 
assessments. Tectonic events have such a potential at Yucca Mountain. 
Rates of displacement on the nearest potentially significant fault in 
the region average about 0.02 mm/yr. (DOE, Science & Engineering 
Report, 2002, p. 4-409, Docket No. EPA-HQ-OAR-2005-0083-0069) This 
means that in 10,000 years, there could be 20 cm (0.65 ft) of 
displacement, a relatively small change not likely to affect 
performance of the geologic system. However, in 1 million years, the 
same rate of movement results in 20 m (65 ft) of displacement on the 
fault. Using the larger estimates of movement within the range of 
potential movement, displacement could be as much as 30 m (100 ft) over 
1 million years. Such changes in the geologic setting at Yucca Mountain 
have the potential to erode the scientific basis for performance 
assessment and possibly to affect the quality of the information the 
assessment can provide to decision-makers.
    NAS also stated that ``we see no technical basis for limiting the 
period of concern to a period that is short compared to the time of 
peak risk or the anticipated travel time.'' (NAS Report p. 56) This 
statement suggests that the stability period must be long enough to 
allow FEPs that pass the probability and significance screens to 
demonstrate their effects, if any, on the results of the performance 
assessments, even from waste package failures occurring relatively late 
in the period. In contrast to the accumulated small-scale changes 
discussed above, larger-scale seismic events are more likely to 
contribute directly to radionuclide releases through the effects of 
ground motion. Strong seismic events could damage waste package 
integrity by causing emplacement drift collapse or vigorous shaking of 
the packages themselves. Earthquake recurrence intervals for the site 
indicate that strong events could reasonably be assumed to test waste 
package integrity at various times within the 1 million-year period 
(Docket No. EPA-HQ-OAR-2005-0083-0374 and 0379). In addition, we note 
that estimates of ground water travel time from the repository to the 
RMEI location are on the order of thousands of years (see the BID for 
the 2001 final rule, Docket No. EPA-HQ-OAR-2005-0083-0050). At these 
rates, the effects of disruptive volcanic and seismic effects on 
releases would not be delayed from reaching the RMEI location during 
the stability period, e.g., added releases from a low probability 
seismic event at 800,000 years would have ample time to be captured by 
the performance assessments. Based on these considerations, the 1 
million-year period is a sufficiently long time frame to evaluate the 
potential consequences of both gradual processes and disruptive events 
on disposal system performance.
    In summary, for regulatory policy as well as site-specific 
scientific considerations, we believe that fixing the period of 
geologic stability for compliance assessments at 1 million years 
provides a reasonable test for the disposal system performance. We 
believe a fixed time period is necessary both to provide a definitive 
marker for compliance decision-making and to prevent unbounded 
speculation surrounding the factors affecting engineered barrier 
performance and the ultimate timing of peak dose projections. 
Examination of site characteristics indicates that the influences of 
natural processes and events on release and transport of radionuclides 
would be demonstrated even for waste package failures occurring 
relatively late in the period. We believe that setting a 1 million year 
limit is a cautious but reasonable approach consistent with the NAS 
position on bounding performance assessments for uncertain elements 
affecting disposal system performance. Finally, explicitly defining the 
period during which our standards apply will focus attention on times 
for which the geologic setting and associated processes are more 
quantifiable and boundable, rather than entering debate on disposal 
system performance in time periods where the fundamental geologic 
regime may have sufficiently changed so that the ``scientific basis for 
performance assessment is substantially eroded and little useful 
information can be developed.'' (NAS Report p. 72)
9. How Will NRC Judge Compliance?
    Today's final rule directs NRC to use the arithmetic mean of the 
distribution of projected doses to determine compliance with both the 
150 [mu]Sv/yr (15 mrem/yr) dose standard applicable for the first 
10,000 years after closure and the 1 mSv/yr (100 mrem/yr) peak dose 
standard applicable between 10,000 and 1 million years after closure. 
In reaching this decision, we considered comments raising legal, 
technical, and policy points. Foremost among these were comments 
focusing on a statement by the NAS committee: ``We

[[Page 61278]]

recommend that the mean values of calculations be the basis for 
comparison with our recommended standards.'' (NAS Report p. 123)
    After considering public comments, the NAS Report, and the DC 
Circuit decision, we conclude that the use of the arithmetic mean to 
determine compliance at all times, without conditions or restrictions, 
is straightforward and clearly consistent with the NAS recommendation, 
pursuant to the EnPA. Consistent with our proposal, we are specifying 
that the ``mean'' to be used is the arithmetic mean, as this is 
consistent with the intent of 40 CFR part 191 and its implementation at 
WIPP. See section 7 of the Response to Comments document for more 
discussion of the points raised in public comments.
10. How Will DOE Calculate the Dose?
    Today's final rule requires DOE to calculate the annual committed 
effective dose equivalent (CEDE) for comparison to the storage, 
individual-protection, and human-intrusion standards using the 
radiation- and organ-weighting factors in ICRP Publication 60 (``1990 
Recommendations of the ICRP''), rather than those in ICRP Publication 
26 (``1977 Recommendations of the ICRP''). As we described in our 
proposal, this action will incorporate updated scientific factors 
necessary for the calculation, but will not change the underlying 
methodology. We explained in some detail the use of the terms 
``effective dose equivalent'' and ``effective dose'' in the EnPA, the 
DC Circuit decision, the ICRP publications, and our previous actions to 
support our position that use of the weighting factors in ICRP 60 (and 
its follow-on implementing Publication 72) is consistent with 
calculation of effective dose equivalent, as required by the EnPA. (70 
FR 49046-49047)
    We received some comment disagreeing with our conclusion that use 
of the term ``effective dose equivalent'' is consistent with the use of 
the ICRP 60 weighting factors. As we discussed in our proposal, we 
believe a close reading of ICRP 60 supports our interpretation that 
effective dose equivalent and effective dose are synonymous concepts. 
ICRP defined two weighting factors in ICRP 26, the radiation quality 
factor, Q, and the tissue weighting factor, WT. In ICRP 60, 
the quality factor was replaced by the radiation weighting factor, 
WR, with the same values assigned to alpha, beta, and gamma 
radiation. In ICRP 26, the tissue weighting factor was presented as a 
rigid construct with defined values for specific organs. In ICRP 60, 
the tissue weighting factor was redefined as a set of recommended 
values for an expanded set of organs (which could be modified in cases 
where scientific information was available to support using alternative 
factors), and it was explained that the attributes of the tissue 
weighting factor include the components of detriment cited by the 
comments (fatal and non-fatal cancers, length of life lost, and 
hereditary effects). However, ICRP made a clear distinction between its 
renaming of the doubly weighted dose quantity from ``effective dose 
equivalent'' (ede) to ``effective dose'' (E) and its redefining of 
WT. The association of effective dose equivalent with the 
ICRP 26 tissue weighting factors is thus coincidental but not required. 
We cited ICRP to that effect in our proposal:

    The weighted equivalent dose (a doubly weighted absorbed dose) 
has previously been called the effective dose equivalent but this 
name is unnecessarily cumbersome, especially in more complex 
combinations such as collective committed effective dose equivalent. 
The Commission has now decided to use the simpler name effective 
dose, E. The introduction of the name effective dose is associated 
with the change to equivalent dose, but has no connection with 
changes in the number or magnitude of the tissue weighting factors * 
* *

ICRP Publication 60, p. 7, paragraph 27, Docket No. EPA-HQ-OAR-2005-
0083-0421, emphasis added.

    Similarly, ICRP also states:

    The values of both the radiation and tissue weighting factors 
depend on our current knowledge of radiobiology and may change from 
time to time. Indeed, new values are adopted in these 
recommendations * * *. It is appropriate to treat as additive the 
weighted quantities used by the Commission but assessed at different 
times, despite the use of different values of weighting factors. The 
Commission does not recommend that any attempt be made to correct 
earlier values. It is also appropriate to add values of dose 
equivalent to equivalent dose and values of effective dose 
equivalent to effective dose without any adjustments.

ICRP Publication 60, p. 9, paragraph 31, Docket No. EPA-HQ-OAR-2005-
0083-0421, emphases added.

    In summary, we believe the intent of Congress in specifying 
effective dose equivalent is that the Yucca Mountain standards be based 
on a doubly weighted dose quantity, not that the assessment of that 
quantity be tied to factors developed at a particular time, when newer 
science indicates those factors should be updated. We use effective 
dose equivalent for consistency with the terminology used in the EnPA, 
but are adopting in today's final rule the current recommended values 
for WT. Our approach is thus fully consistent with both the 
current ICRP recommendations and the EnPA.
    Today's final rule does incorporate a change to the proposed 
definition of ``effective dose equivalent'' in Sec.  197.2 to make it 
consistent with language in Appendix A regarding the potential use of 
future ICRP recommendations. We received some comments suggesting that 
the appendix should not include specific weighting factors, but state 
only that doses are to be calculated in accordance with the methods of 
ICRP 60/72. The commenter believes this is appropriate because NRC's 
proposed licensing requirements included the tissue weighting factors, 
but not the radiation weighting factors. Further, the commenter points 
out that dose coefficients in ICRP 72 (and Federal Guidance Report 13) 
consider a somewhat different set of organs than do the tissue 
weighting factors. We prefer not to adopt the commenter's suggestion, 
which we believe could lead to questions regarding the appropriate 
factors to use. We note that ICRP 60, unlike ICRP 26, is not tied to a 
specific set of weighting factors, and allows for the possibility that 
users will substitute their own preferred set of factors. Stating only 
that the methods of ICRP 60/72 be used to calculate dose, without the 
additional stipulations in the appendix, would not provide sufficient 
clarity on this point. Therefore, we are adding language to the 
definition in Sec.  197.2 to the effect that NRC can direct that other 
weighting factors be used to calculate dose, consistent with the 
conditions presented in Appendix A. We believe this will effectively 
address the commenter's concern.

B. How Will This Final Rule Affect DOE's Performance Assessments?

    Today's final rule requires DOE to demonstrate compliance with the 
individual-protection standard through use of performance assessment. A 
performance assessment is developed by first compiling lists of 
features (characteristics of the disposal system, including both 
natural and engineered barriers), events (discrete and episodic 
occurrences at the site), and processes (continuing activity, gradual 
or more rapid, and which may occur over intervals of time) anticipated 
to be active during the compliance period of the disposal system. These 
items are collectively referred to as ``FEPs'' (features, events, and 
processes). Once FEPs are identified, they are evaluated for their 
probability of occurrence (i.e., how likely they are to occur during 
the compliance period) and their effect on the results of the 
performance assessment (i.e., do they significantly

[[Page 61279]]

affect projected doses from the disposal system during the first 10,000 
years after disposal). Addressing these aspects of performance 
assessment for a compliance period of 1 million years was a central 
aspect of our proposal and is the focus of this section.
    After considering public comments, we are retaining Sec.  197.36 as 
proposed, with two modifications. First, the probability threshold for 
FEPs to be considered for inclusion in performance assessments 
conducted to show compliance with Sec.  197.20(a)(1) is now stated as 
an annual probability of 1 in 100 million (10-8 per 
year).\33\ Because the same FEPs included in these performance 
assessments will also be included in performance assessments conducted 
to show compliance with Sec.  197.20(a)(2), the same probability 
threshold applies in all cases. Second, we are adding a provision to 
address a potential effect of seismicity on hydrology that was 
identified by NAS. The final rule now requires the potential effects of 
a rise in the ground-water table as a result of seismicity to be 
considered. If NRC determines such effects to be significant to the 
results of the performance assessment, it shall specify the extent of 
the rise for DOE to assess.
---------------------------------------------------------------------------

    \33\ Only FEPs with an annual probability greater than or equal 
to 10-5 need to be considered in performance assessments 
to show compliance with Sec. Sec.  197.25(b) and 197.30. FEPs below 
this probability threshold, but still above 10-8 per 
year, are defined by NRC as ``unlikely''.
---------------------------------------------------------------------------

    Our 2001 rule set forth three basic criteria for evaluating FEPs 
for their potential effects on site performance and their incorporation 
into the scenarios used for compliance performance assessments (Sec.  
197.36). These criteria retained the same limitations originally 
established in 40 CFR part 191, which were developed to apply to any 
potential repository for spent nuclear fuel, high-level waste, or 
transuranic radioactive waste. We believe that approach remains 
reasonable for the site-specific Yucca Mountain standards, and we 
believe it is desirable to maintain consistency between the two 
regulations for geologic repositories in the basic criteria for 
evaluating FEPs. The criteria for evaluating FEPs are:
     A probability threshold below which FEPs are considered 
``very unlikely'' and need not be included in performance assessments;
     A provision allowing FEPs above the probability threshold 
to be excluded from the analyses if they would not significantly change 
the results of performance assessments; and
     An additional stipulation that in addition to ``very 
unlikely'' FEPs, ``unlikely'' FEPs need not be considered in 
performance assessments conducted to show compliance with the human-
intrusion and ground-water protection standards.
    As an initial step, a wide-ranging set of FEPs that potentially 
could affect disposal system performance is identified. The term 
``potentially'' is key here, because at this early stage, the list is 
deliberately broad, focusing more on ``what could happen'' rather than 
``what is likely to happen at Yucca Mountain.'' Under the 2001 rule, 
each of these FEPs is then examined to determine whether it should be 
included in an assessment of disposal system performance over a 10,000-
year period by evaluating the probability of occurrence at Yucca 
Mountain and, as appropriate, the effects of the FEP on the results of 
the performance assessment. Based on these evaluations, a FEP may be 
excluded from the assessment of disposal system performance on the 
basis of probability, or if the results of the performance assessments 
would not be changed significantly by its exclusion.
    We included in our proposal provisions describing how FEPs should 
be incorporated into assessments of disposal system performance during 
the period of geologic stability, defined as ending at 1 million years 
after closure. Our purpose was to build upon the provisions applicable 
to the 10,000-year compliance period in our 2001 rule to address the 
complexities introduced by extending the compliance period to 1 million 
years. In general, the database of FEPs applicable to Yucca Mountain 
should be the same, regardless of the period covered by the 
assessments. In developing our proposal, however, we considered how 
these general provisions might change when the compliance period 
extends to 1 million years. We also proposed specific provisions to 
address climate change, seismicity, and igneous events, which were 
identified by NAS as potential ``modifiers'' whose effects could be 
bounded within the period of geologic stability.
    Some commenters questioned whether our authority to establish 
public health protection standards for Yucca Mountain extended to 
specifying how FEPs must be considered, contending that this function 
properly lies with the implementing authority (NRC). We disagree. While 
NRC clearly has authority to specify such provisions, it is also within 
our purview to stipulate such conditions as are necessary to place our 
regulations in context and ensure they are implemented as we intended. 
For analyses covering 1 million years, it is important to focus on 
those factors most affecting performance, if necessary by excluding 
other aspects that are more likely to have little or no significance. 
We believe this approach is consistent with the direction from NAS. NAS 
was charged with providing advice to EPA on ``reasonable standards for 
protection of public health and safety'' (EnPA section 801(a)(2)). NAS 
provided its findings and recommendations in the context of standards 
to be developed by EPA, including discussion of FEPs, for example: 
``the radiological health risk from volcanism can and should be subject 
to the overall health risk standard to be required for a repository at 
Yucca Mountain.'' (NAS Report p. 95) Further, NAS discussed the 
question of uncertainty in quantifying physical and chemical processes 
and their operation over long time periods and the inevitability of 
``residual, unquantifiable uncertainty,'' stating ``[t]he only defense 
against it is to rely on informed judgment.'' (NAS Report p. 80) 
Therefore, we believe it appropriate to specify, where necessary, 
additional provisions for the treatment of FEPs in disposal system 
assessments to avoid boundless speculation. We have explained our 
understanding of the proper use of bounding performance scenarios, and 
we believe we are consistent with the NAS on this point. Bounding 
assessments addressing uncertainty in understanding the long-term 
behavior of the site should be constructed using informed judgment, not 
speculative assumptions without credible supporting evidence.
    Two of the criteria for evaluating FEPs, probability and 
significance of the impacts on performance assessments, are of primary 
importance in considering how the provisions applicable to the 10,000-
year period might change when the compliance period is extended to 1 
million years. In the proposed rule, we concluded that the 10,000-year 
FEPs screening could serve as an adequate basis for longer-term 
assessments because it is sufficiently inclusive to be appropriate for 
the entire 1 million-year compliance period, while at the same time 
reasonably bounding the scenarios that must be considered over the 
longer time frame. We thought our statements in the preamble on this 
point were sufficiently clear, but we understand that the way we 
structured Sec.  197.36 of the proposal, essentially separating the two 
time periods, may have caused some confusion. For example, we did not 
intend to indicate or imply that the

[[Page 61280]]

post-closure performance assessments would consist of two separate and 
dramatically different calculations, with each having distinctly 
different scenario construction, parameter value distributions, or 
other attributes. Regardless of the standard against which compliance 
is being judged, the probability of occurrence and the significance of 
the impacts on performance assessment are the two primary criteria for 
including a FEP in the compliance analysis. The screening for FEPs is 
done for the 10,000-year performance assessment and then used with 
certain additions set forth in the rule for the 1 million-year peak 
dose performance assessment. The initial screening provides a database 
of FEPs, which is then used for both the 10,000-year and post-10,000-
year peak dose analyses, with some additional stipulations for the 
period beyond 10,000 years. The discussion that follows addresses each 
of these screening criteria in turn.

Probability

    In the proposed standards, we defined the probability threshold for 
``very unlikely'' FEPs as a 1 in 10,000 chance of occurrence within 
10,000 years, or roughly a 1 in 100 million (10-8) chance 
per year of occurring. In today's final rule, the probability threshold 
is now stated only as an annual probability of 1 in 100 million 
(10-8). We believe it is appropriate to clarify that FEPs 
have associated probabilities of occurrence that generally do not 
change over time. That is, the database of FEPs deemed sufficiently 
probable would serve equally well as the basis for assessments covering 
1,000, 10,000, 100,000, or 1 million years. These probabilities of 
occurrence are established by examining the geologic record and 
considering potential mechanisms for components of the repository and 
its natural setting to undergo changes. FEPs with a probability of 
occurrence greater than 1 chance in 100 million per year should be 
considered for inclusion in the performance assessments to show 
compliance with the 10,000-year individual-protection standard, and the 
same FEPs included in those assessments should be used to develop the 
performance assessment scenarios to be analyzed for the peak dose 
performance assessments between 10,000 and 1 million years. We believe 
that this is an inclusive threshold level that fully considers a range 
of low-probability FEPs, while at the same time limiting speculation 
over highly improbable FEPs. We believe the probability screening 
threshold provides the foundation for a reasonable test of the disposal 
system, as discussed further below.
    Although we discussed the meaning of the probability threshold in 
some detail in our proposal, we emphasize it again as the foundation 
for constructing the performance assessment. A 1 in 100 million annual 
probability of occurrence, when considered over a 10,000-year period, 
includes FEPs with a cumulative chance of occurring of one one-
hundredth of one percent (0.01%). Similarly, over 1 million years, the 
cumulative probability increases to only a one percent (1%) chance of 
occurrence within that time frame. We believe that the database of 
information necessary to assess FEPs at this low probability is the 
same as that necessary for examining their importance over the entire 1 
million-year compliance period. We believe this probability criterion 
leads to an inclusive set of potential FEPs for both the 10,000-year 
and peak dose assessments, and in our view would support a reasonable 
test of the disposal system that encompasses the climate change, 
seismic, igneous, and corrosion scenarios specified in our proposal.
    In our proposed rule, we concluded that the 10,000-year FEPs 
screening could serve as an adequate basis for longer-term assessments 
because it is sufficiently inclusive to be appropriate for use in 
developing performance scenarios applicable to the entire 1 million-
year compliance period. That is, we did not propose to require DOE to 
consider FEPs with an annual probability lower than 10-8 to 
accommodate the lengthened compliance period. We believe excluding FEPs 
with less than a 1% chance of occurrence in 1 million years is 
consistent with the principles of reasonable expectation. We believe 
that lowering the annual probability level below 10-8 would 
allow for speculative scenarios to be considered in the peak dose 
performance assessment, which would be neither reasonable nor 
justifiable, as explained below.
    Some commenters disagreed, stating that, because we are extending 
the compliance period by a factor of 100, the probability threshold for 
excluding FEPs should also be extended by a factor of 100, resulting in 
a threshold of 1 chance in 10 billion of occurrence per year. 
Similarly, we received some comments questioning altogether the need 
for or validity of a probability threshold. The comments suggest that, 
because the effects are weighted by the probability of occurrence, any 
potential FEP, no matter how unlikely, should be characterized and 
assessed because its influence will be mitigated by its low 
probability. They cite NAS to the effect that ``all these scenarios 
need to be quantified'' with respect to probability and consequence. 
(NAS Report p. 72) Therefore, the commenters conclude that our concerns 
about introducing excessive speculation are unfounded. We disagree. We 
addressed this topic in our proposal, in the expectation that we would 
be encouraged to adjust the probability threshold by two orders of 
magnitude (i.e., widening the probability range by a factor of 100) to 
account for the similarly lengthened compliance period. We believe that 
simply extending the approach of using a one in 10,000 probability over 
a 1 million-year period to give 1 in 10 billion chance per year of 
occurring (10-10) would result in the inclusion of FEPs that 
are so speculative as to be unreasonable (70 FR 49052). Nor do we 
believe it would be consistent with NAS's view that the overall goal 
was ``to define a standard that specifies a high level of protection 
but that does not rule out an adequately sited and well-designed 
repository because of highly improbable events.'' (NAS Report p. 28) 
Further, NAS itself suggested situations in which scenarios need not be 
quantified. NAS discusses, in the context of volcanism, a 
10-8 annual probability of occurrence as a level that 
``might be sufficiently low to constitute a negligible risk'' below 
which ``it might not be necessary to consider'' how the event might 
contribute to releases from the disposal system. (NAS Report p. 95) We 
believe this example is instructive, given that volcanism is the single 
scenario resulting in direct release of radioactive material from the 
repository into the biosphere, resulting in relatively immediate 
exposures. We believe it is reasonable to extend the concept expressed 
by NAS as ``negligible risk'' to FEPs whose influences are seen in the 
gradual release and transport of radionuclides over long periods of 
time. Therefore, we believe that lowering the probability threshold, or 
eliminating it altogether, would be inconsistent with the important NAS 
cautions to focus assessment efforts on FEPs that can be bounded within 
the limits of geologic stability.
    In our view, were we to lower or eliminate the probability 
threshold, it would be necessary to consider and describe FEPs that 
might have been present or occurred only the initial years of the 
planet's existence. Similarly, FEPs with an annual probability of 
10-10 may be only hypothetical, since the age of the Earth 
is generally considered to be ``only'' 4.6

[[Page 61281]]

x 10\9\ years, suggesting that these FEPs may have less than a 50% 
chance of occurring within the entire history of the Earth. Indeed, the 
volcanic rocks comprising Yucca Mountain and its surroundings are only 
on the order of 10-12 million years old (~10\7\ years). In determining 
the probability of particular FEPs, the geologic record at the site is 
the source of information to identify what FEPs have occurred at the 
site in the past and may occur in the future (through the period of 
geologic stability). Since the host rock formations at the site are 
only about 10 million years old, an annual probability cut-off of 
10-10 would mean that probability estimates for some FEPs 
would have to be made in spite of the fact that there is no evidence 
for their occurrence at the site in the past. As it is, the 
10-8 probability threshold presents a significant challenge 
to characterize FEPs with some degree of confidence, given the limits 
of today's science and technology. ICRP makes a similar point in its 
2007 recommendations: ``The use of probability assessment is limited by 
the extent that unlikely events can be forecast. In circumstances where 
accidents can occur as a result of a wide spectrum of initiating 
events, caution should be exercised over any estimate of overall 
probabilities because of the serious uncertainty of predicting the 
existence of all the unlikely initiating events.'' (Publication 103, 
Docket No. EPA-HQ-OAR-2005-0083-0423, paragraph 269) (Note that this 
discussion is in the context of ``potential'' exposures, which include 
releases that may occur in the far future from disposal facilities. 
Therefore, the term ``accidents'' should not be taken as limited to 
operational activities.) Overall, we believe events with a lower annual 
probability than 10-8 would introduce speculation beyond 
what is appropriate to define a reasonable test of disposal system 
performance.
    We also received comments stating that maintaining the probability 
screening criteria for the extended compliance period undermines our 
arguments for increasing uncertainty. To the contrary, we believe the 
physical meaning of the probability threshold (0.01% chance of 
occurrence within 10,000 years, but a 1% chance within 1 million years) 
appropriately incorporates the concept of uncertainty increasing with 
time, while still applying a substantially conservative screening 
criterion.
    We believe that the guidance we have provided for executing a FEPs 
evaluation and screening process assures that it is executed in a 
thorough manner. For example, we have stated that the geologic record 
through the Quaternary Period (a period extending back approximately 2 
million years from today) at and around the site should be examined to 
identify relevant FEPs. While we believe that the Quaternary Period 
offers the most reliable data for identifying and characterizing site 
geologic FEPs, we do not believe that evidence preserved in older 
portions of the geologic record should be ignored in the FEPs 
identification process. We did not mean to imply that DOE need only 
consider the previous 10,000 years when developing evidence for the 
probability of occurrence of future events. Rather, our statements 
regarding the Quaternary Period as an appropriate geologic record were 
intended to confirm that, where available, reliable geologic records 
for earlier time periods should be consulted. For example, determining 
the probability of seismic and igneous events would make use of the 
geologic record at the site for as far back in time as reliable 
estimates of past events can be made so that defensible probability 
estimates can be made. We believe the Quaternary Period offers the best 
information to quantify the probabilities and consequences of geologic 
FEPs relevant to site performance. However, we did not intend that 
significant information about FEPs be ignored simply because that 
information appears in the geologic record at the site prior to the 
Quaternary Period.
    In fact, a longer portion of the geologic record has been examined 
by DOE and NRC in developing FEP probabilities. For example, to 
determine the nature and frequency of volcanic activity around Yucca 
Mountain, volcanic activity around the site through the Quaternary 
Period was extensively examined, as well as volcanic activity prior to 
that time (ACNW Workshop on Volcanism at Yucca Mountain, September 22, 
2004--Docket No. EPA-HQ-OAR-2005-0083-0373 and 0378). We believe that 
the information necessary to evaluate FEPs against the probability 
threshold we established (10-8 annual probability) will be 
extensive, and that increasing the compliance period from 10,000 to 1 
million years does not require that additional studies be performed 
beyond those necessary to derive the FEPs probabilities under the 
screening process done for the 10,000-year time frame assessments. As 
we have noted previously, the probabilities for individual FEPs are 
determined once, and the same probabilities are used in both the 
10,000-year and 1 million-year assessments.
    On this last point, we stress that the revised Sec.  197.36(a) 
issued today should not be interpreted as compelling DOE to extend the 
databases for its technical justifications. We are restating the 
probability screening criterion, not recasting the entire framework for 
the analysis. We recognize that in any licensing process the burden of 
proof is on the applicant to demonstrate that the necessary factors and 
influences have been evaluated. It must also be recognized that there 
will always be limits to the ability of science and technology to 
characterize FEPs and their effects on the disposal system. However, 
NAS has stated that many of these processes and their uncertainties are 
boundable. In our judgment, given the capabilities of today's science 
and technology, it would be contrary to the principle of reasonable 
expectation to require DOE to demonstrate the same level of confidence 
in assessments covering 1 million years as it would for a much shorter 
10,000-year analysis.
    Similarly, we believe that this clarification does not create the 
prospect of speculative scenarios of very low probability (from 
combinations of FEPs) being proposed, thereby opening the performance 
assessments to unbounded speculation. For example, if two low 
probability independent FEPs were proposed to occur simultaneously 
because of the longer time horizon under consideration, the probability 
of that combination would be the product of their respective 
probabilities. In other words, the probability of the combined FEPs 
occurring during the same year will be much lower, by possibly orders 
of magnitude, than the probability of either FEP occurring 
individually. Therefore, since the contributions of various FEPs (or 
scenarios) to the dose assessments is the product of their respective 
probabilities and consequences, the consequence of the combined FEPs 
would need to be inversely proportionally higher, typically by orders 
of magnitude, than the combined consequences of the individual FEPs 
considered separately, in order to make a significant change in the 
overall dose assessment.
    We did receive some comment suggesting that we had inappropriately 
excluded the type of volcanic events that created the Yucca Mountain 
tuff some 12 to 14 million years ago, instead focusing on the past 
several million years. However, as we stated in our proposal, the 
geologic record of the past several million years in the area around 
the site indicates that basaltic volcanism is the type of volcanism 
that has occurred recently and has the potential to recur in the 
future. The earlier events

[[Page 61282]]

were of a much different, cataclysmic nature, producing rock units more 
than 6000 ft (1800 m) thick. The type of volcanic activity that created 
Yucca Mountain and the surrounding area has not recurred over the 
approximately 10 million years since the deposits were originally laid 
down and is extremely unlikely to occur within the next 1 million years 
(Docket No. EPA-HQ-OAR-2005-0083-0050, pp. 7-42 through 7-49). Further, 
we question whether such cataclysmic events could be reasonably 
considered to fall within the bounds of geologic stability as 
envisioned by NAS. Inclusion of such events in the peak dose assessment 
up to 1 million years would be inconsistent with the intent of the NAS 
when it noted that long-term performance can be assessed (because 
physical and geologic processes are sufficiently quantifiable, and the 
related uncertainties sufficiently boundable) when the geologic system 
is relatively stable or varies in a boundable manner. (NAS Report p. 9) 
However, NAS noted that ``[a]fter the geologic environment has changed, 
of course, the scientific basis for performance assessment is 
substantially eroded and little useful information can be developed.'' 
(NAS Report p. 72) We believe that volcanism of that magnitude would 
result in fundamental change of the geologic environment and would not 
represent a reasonable test of the disposal system. Therefore, we 
continue to see no basis for requiring this type of event be included 
in the performance assessment.
    Some may view our approach using a single probability threshold for 
determining which FEPs should be considered for inclusion in the 
performance assessments as inconsistent with the application of 
different dose standards for the initial 10,000 years and the period up 
to 1 million years. We do not see an inconsistency primarily because 
the nature and effects of uncertainty on event probability and dose 
projections are dissimilar. The overall uncertainty in projecting doses 
using a model simulating the complex interplay of the disposal system 
components over long times, each of which has inherent uncertainties in 
their characteristics, and the associated difficulty in relying on such 
projections for regulatory decisions, should not be confused with the 
uncertainty implied in assigning a probability of occurrence to a 
particular FEP, which in many cases derives from an examination of the 
geologic record at the site. We have noted the difficulty in 
extrapolating performance to very long times, and believe it is 
appropriate to address this difficulty by establishing a somewhat 
higher, but still protective, dose limit for the period beyond 10,000 
years. FEP probabilities are assigned based on observations that may 
cover long periods of time, such as for geologic processes, or from 
laboratory testing and the extrapolation of such results to conditions 
that may exist in the distant future, such as for corrosion processes. 
In today's final rule, the FEP probability threshold that must be 
considered in developing performance assessments represents a policy 
judgment about how such events should be addressed in order to meet the 
regulatory challenge recognized by NAS, supported by technical 
reasoning about the nature of the site database for identifying and 
characterizing FEPs.

Significance

    The second criterion for evaluating FEPs, the evaluation of the 
significance of the impacts on performance assessment, allows FEPs 
above the probability threshold to be excluded from the analyses if 
they would not significantly change the results of performance 
assessments. In other words, this evaluation is intended to identify 
those FEPs whose projected probability would otherwise make them 
candidates for inclusion in the performance assessment, but whose 
effect on repository performance (however probable) can be demonstrated 
not to be significant. We are retaining the provisions presented in the 
proposed rule related to screening FEPs for their effects on the 
performance assessment results, and, for the reasons discussed below, 
are adding an additional provision regarding the analysis of seismic 
FEPs in Sec.  197.36(c).
    Today's final rule continues to focus on seismic and igneous events 
that cause direct damage to the engineered barrier system (e.g., 
repository drifts and waste packages). Regardless of other effects of 
these events on the disposal system, the timing and degree of waste 
package degradation has a significant effect on peak dose. The 
longevity of waste packages, when considering periods of hundreds of 
thousands of years, is uncertain and dependent on a number of factors. 
Therefore, the aspect of primary interest in evaluating seismic and 
igneous FEPs is their potential to breach waste packages and make 
radioactive material available for transport by infiltrating water (or, 
in the case of volcanic events, for direct release into the biosphere).
    We believe that the use of the significance criterion of Sec.  
197.36(a) would assure a reasonable test of disposal system performance 
through the period of geologic stability. We recognize that setting 
forth the significance screening criterion in Sec.  197.36(a) of our 
proposal as pertaining to the 10,000-year period could be construed as 
creating a situation in which important long-term processes could be 
excluded altogether from the analysis if they were not significant in 
the earlier period. However, we do not believe it is reasonable to 
interpret the significance criterion in this way. We have taken 
specific steps to ensure that significant long-term FEPs will be 
considered in the assessments. Consistent with NAS, we have addressed 
the long-term effects of seismic, igneous, and climatic FEPs. In 
addition, as described below, we have directed that the effects of 
general corrosion on the engineered barrier system be evaluated. 
Further, contrary to some comments, we explicitly required that FEPs 
included in the 10,000-year analysis must continue to be included for 
the longer-term (10,000 years to 1 million years) assessment. That is, 
FEPs included in the initial 10,000-year assessments will continue to 
operate throughout the period of geologic stability. These FEPs are 
already identified as appropriate for inclusion, and include 
fundamental physical and geologic processes that play roles in the 
release and transport of radionuclides, regardless of the time period 
covered by the assessment.
    As noted above, to further bolster the significance screening 
criterion, in our proposal we considered whether it might be possible 
that FEPs eliminated from consideration during the first 10,000 years 
should be included in the longer-term assessment if they would have a 
significant bearing on performance at later times, even if they could 
legitimately be dismissed for the initial 10,000-year period. We 
focused our attention on FEPs affecting the engineered barriers since, 
as noted above, waste package failure is the dominant factor in the 
timing and magnitude of the peak dose, and is the primary reason for 
considering time frames up to 1 million years. To illustrate one 
consideration, thermal conditions in the repository change dramatically 
within the initial 10,000-year period, affecting the relative 
importance of some FEPs during and after the thermal pulse. However, 
FEPs involved in release and transport of radionuclides would generally 
be the same, regardless of when the waste package fails. Further, while 
FEPs associated with the natural characteristics of the site are active 
today or can be observed in the geologic

[[Page 61283]]

record, FEPs related to engineered barrier longevity involve 
extrapolation of shorter-term testing data. The degree to which natural 
FEPs can contribute to the breaching of waste packages is dependent to 
a large extent on the condition of those packages over time, making 
FEPs specific to the engineered barriers of particular importance. We 
took this approach for two reasons. First, we needed to clearly outline 
the reasons why a FEP that could be excluded on the basis of 
significance from the performance assessments for the initial 10,000-
year period might potentially need to be re-considered for the 
lengthened compliance period. Second, we wanted to further our goal of 
issuing an implementable standard by limiting potentially unconstrained 
speculation over the longer compliance period. By discussing the 
considerations involved in evaluating FEPs that could be previously 
excluded, we hoped to lay out clearly the reasoning that could be used 
to justify inclusion of additional FEPs beyond those identified by the 
NAS committee.
    We explicitly addressed general corrosion of the waste packages and 
other engineered barriers in our proposal because it is likely to be a 
significant degradation process at later times. We identified this FEP 
as being significant at times greater than 10,000 years because we 
believe it is the principal process FEP that could lead to ``gross 
breaching'' of the waste package over those extended time frames. 
Processes and events that could lead to ``gross breaching'' are of 
greatest significance to long term performance because, as noted by the 
NAS, ``canisters are likely to fail initially at small local openings 
through which water might enter, but out of which the diffusion of 
dissolved wastes will be slow until the canister is grossly breached.'' 
(NAS Report p. 86) It is the time of ``gross breaching'' that 
determines the time of more rapid release of dissolved wastes from the 
repository and hence may have a significant effect on the time and 
magnitude of the peak dose within 1 million years. Although the general 
corrosion process is slow, tends to decrease with decreasing 
temperature, and may not lead to significant releases for the first 
10,000 years (depending on DOE's design of the waste package), we 
believe this FEP could be significant enough over the long term to 
require inclusion in the assessment of performance during the time of 
geologic stability, regardless of the screening decision in the first 
10,000 years. Further, consideration of the uncertainties involved in 
extrapolating general corrosion data for the proposed waste package 
materials supports the inclusion of this potentially highly significant 
process (``Assumptions, Conservatisms, and Uncertainties in Yucca 
Mountain Performance Assessments,'' Docket No. EPA-HQ-OAR-2005-0083-
0085, section 5.4.1). Therefore, we believe that general corrosion, in 
addition to those FEPs related to seismicity, igneous activity and 
climate change identified by NAS, requires explicit inclusion in the 
assessments during the time of geologic stability.
    We did, as one commenter pointed out, consider providing NRC more 
latitude to identify FEPs if they would significantly affect the peak 
dose. After further consideration, we decided against this approach, 
believing the provisions outlined above and the specification of 
general corrosion would adequately address this situation, provide a 
reasonable test of disposal system performance, and give DOE the 
necessary assurance that the important factors have been explicitly 
identified in the rule. As we noted above, we identified general 
corrosion of engineered barriers as a FEP potentially significant to 
the peak dose, and specified its inclusion because it is likely to be a 
significant degradation process at later times. Similarly, consistent 
with the NAS recommendations, we have specified the inclusion of 
climate change, seismicity, and igneous scenarios. We view the 
requirement to include general corrosion, as well as the climate, 
seismic, and igneous scenarios identified by NAS, as leading to an 
effective and extensive assessment, which can fairly be represented as 
a reasonable test of the disposal system. As we discussed in our 
proposal, the search for additional FEPs that might be significant at 
some point beyond 10,000 years can rapidly become highly speculative 
and limited in benefit. Therefore, we continue to believe that our 
approach represents ``informed judgment'' and a reasonable test of 
repository performance over time frames as long as 1 million years for 
the Yucca Mountain disposal system.
    We also note that DOE submitted, as part of its comments on the 
proposed rule, the results of analyses based on a simplified peak dose 
model (Docket No. EPA-HQ-OAR-2005-0083-0352, Appendix 1). DOE states 
that it had compiled a database of FEPs, independent of compliance 
period, and evaluated them for inclusion in a 10,000-year analysis. DOE 
``subsequently re-evaluated the FEPs over the period beyond 10,000 
years'' and concluded that those FEPs excluded on the basis of 
significance within 10,000 years would also not have significant 
effects on performance projections beyond 10,000 years. DOE reached its 
conclusion both for FEPs excluded ``on a low consequence basis that is 
not affected by time'' and for ``gradual and continuing processes'' 
that ``are time dependent.''
    Also as part of its comments, DOE submitted an analysis that 
identified three reasons why gradual and/or infrequent FEPs excluded on 
the basis of significance within 10,000 years would also not have 
significant effects on performance projections beyond 10,000 years: (1) 
An excluded FEP was determined to be of secondary importance to the 
primary significant degradation FEP, which was included in the 
analysis; (2) the inclusion of the FEP would tend to lower the peak 
dose during the time of geologic stability because it resulted in 
earlier and more diffuse releases (hence the exclusion of the FEP would 
be conservative from a peak dose perspective); or (3) the FEP is 
correlated in some way with temperature (e.g., in the rate with which 
it operates), so it would be less significant at later times due to the 
lower temperature in the repository over time. (Docket No. EPA-HQ-OAR-
2005-0083-0352, Appendix 1, section 6.1 and Table 24) DOE considered 
FEPs of this nature associated with both the engineered and natural 
barrier systems. DOE concluded, for example, that some longer-term 
processes, such as general corrosion, may contribute to waste package 
failure, and disruptive seismic events may contribute to rockfall and 
other physical mechanisms leading to release.
    We also considered public comments on this topic. Most commenters 
who disagreed with our proposal cited the limited data available on 
various corrosion mechanisms that could affect the waste packages. Many 
of these commenters seem to believe that we have excluded all corrosion 
mechanisms except general corrosion. This is not the case. We have 
explicitly directed that general corrosion be considered because it is 
likely to be the most significant such process at longer times; 
however, other corrosion mechanisms (such as localized corrosion) are 
more likely in the early period after disposal when temperatures inside 
the repository are high. If DOE determines these processes to be 
insignificant within 10,000 years, they are not likely to be more 
significant than general corrosion at later times. If they are included 
in the 10,000-year analysis,

[[Page 61284]]

they must be included in the longer-term assessments. One commenter 
highlighted our discussion of criticality as excluding one of the 
``most worrisome threats to the repository'' over the long term. We 
cited an NRC technical study to support our conclusion that such an 
event is unlikely to be significant to the results of the assessments. 
Further, the DOE reference cited above concludes that all criticality 
scenarios fall below the probability screening threshold. An 
alternative view on the FEPs screening process was expressed in a 
report by the Electric Power Research Institute (EPRI): ``Thus, the 
current EPA screening limit is very conservative compared to the 
[Negligible Incremental Dose] level suggested by [NAS]. It is likely 
that there are many FEPs that DOE has already included in their 
analysis using the EPA approach that would not have been included if 
the [NAS]-recommended approach had been followed. Given that many 
additional FEPs are already included, it should be unnecessary to 
include any additional FEPs if the regulatory compliance period is 
extended beyond 10,000 years.'' (``Yucca Mountain Licensing Standard 
Options for Very Long Time Frames,'' April 2005, pp. 3-5 and 3-6, 
Docket No. EPA-HQ-OAR-2005-0083-0087) Taking all of this information 
into account, we continue to believe it is reasonable that, with the 
exception of the specific FEPs identified in 197.36(c), a FEP 
determined to be insignificant in the first 10,000 years may continue 
to be excluded in the post-10,000-year analyses.
    As we noted above, we are modifying the proposed rule regarding the 
provisions related to seismic events in Sec.  197.36(c). We noted in 
our proposal the NAS statement that ``[w]ith respect to the effects of 
seismicity on the hydrologic regime, the possibility of adverse effects 
due to displacements along existing fractures cannot be overlooked'' 
but that ``such displacements have an equal probability of favorably 
changing the hydrologic regime.'' (NAS Report p. 93). We argued that 
these effects would likely be minimal given the many small-scale 
changes that would be possible in the connectivity of the fracture 
networks, and that these effects would likely be small compared to the 
effects of climate change on the hydrologic behavior of the disposal 
system. We did not mean to imply that the seismic and climate events 
would involve the same hydrologic characteristics and processes or 
produce the same effects on the ground-water flow regime, but that the 
effects of one were likely to outweigh the effects of the other. While 
we still believe that is likely, we have concluded, after further 
consideration, that the issue of hydrologic effects resulting from 
seismic events needs to be examined in sufficient detail to address the 
point made by NAS. We believe the effects of fault displacement on the 
hydrologic regime will be adequately addressed by the variation in 
parameters such as hydraulic conductivity (i.e., evaluating reasonable 
variation in ground-water flow parameter values, whether seismically-
induced or not, will illustrate the range of effects that might result 
from seismicity). However, NAS also identified another seismic effect 
on hydrology, namely the potential for transient rise in the ground-
water table. In this instance, NAS did not simply state that such 
potential could be bounded, but noted site-specific studies suggesting 
``a probable maximum transient rise on the order of 20 m or less.'' 
(NAS Report p. 94) Therefore, we now require that the effects of a rise 
in the ground-water table as a result of seismicity be considered. We 
are not specifying the extent of the rise to be considered, but leave 
that conclusion to be determined by NRC. NRC may choose to estimate the 
magnitude of ground-water table rise itself, or require DOE to include 
such estimates in its license application. In this case, however, we 
are also allowing NRC to make a judgment as to whether such a rise in 
ground water would be significant to the results of the performance 
assessment. If NRC determines that such a reasonably bounded scenario 
would not be significant, DOE would not be required to evaluate its 
effects.
    We believe deferring to NRC on this point is the appropriate 
approach. The above quote from page 93 of the NAS Report makes it clear 
that changes to the hydrologic regime from seismic events would be 
equally likely to enhance or reduce transport of radionuclides. 
However, it would seem unlikely for changes to occur that would all 
combine to enhance transport to the saturated zone and then through the 
controlled area, such that concentrations of radionuclides at the RMEI 
location would be significantly increased. It seems more likely that 
localized changes would occur, which in sum would not significantly 
increase overall transport of radionuclides. Further, as noted above, 
we believe these seismically-induced changes are likely to be 
approximated by the normal variation in flow parameters. Changes in the 
hydrologic system from climate change (e.g., increases in infiltration) 
are expected to be quantitatively more significant than such changes 
resulting from seismic activity. We believe NRC is better positioned to 
make judgments regarding the significance and extent of such changes. 
We note that a dozen years of site characterization, scientific study, 
and performance assessments have been conducted since the NAS Report in 
1995. NRC has conducted its own analyses as well as participated in 
ongoing technical exchanges with DOE over this period. We view 
deferring to NRC's judgment in this case as comparable to the approach 
we have taken with climate change. In that instance, we outlined the 
primary issues and overall approach, but specified that NRC would 
establish the details required to implement our standard.
    Finally, we are retaining the provision related to climate change 
as it was proposed. We believe this is a reasonable approach, which 
allows NRC to characterize climate change beyond 10,000 years using 
constant conditions. This approach has the advantage of avoiding 
speculation regarding the timing and magnitude of climatic cycles, 
while addressing the important aspects of climate change. We received 
some comments that appear to have misinterpreted our proposal. Some 
comments suggested that our citation of the NAS statement to the effect 
that ``climate changes on the time scale of hundreds of years would 
probably have little if any effect on repository performance'' (NAS 
Report p. 92) as implying that we are ``ignoring longer-term changes'' 
such as ``glacial periods covering thousands of years.'' This 
represents a fundamental misunderstanding of our proposal, which would 
allow the future climate to be represented by what is essentially a 
glacial transition period lasting 990,000 years, but in any event 
placed no limits on the duration of periods of increased precipitation. 
Similarly, some commenters expressed the view that we ``required'' the 
future climate to be represented by constant conditions, or that we 
were suggesting that a single climate be used in all realizations. On 
the contrary, we cited the NAS conclusion that ``a doubling of the 
effective wetness'' might be significant as one justification for 
stating that it would be reasonable to represent far-future climate by 
constant conditions. Today's final rule, consistent with our proposal, 
leaves it to NRC to determine the parameter values that would define 
the future climate, including influential parameters other than 
precipitation,

[[Page 61285]]

such as temperature. Our specification of the outcome of ``increased 
water flow through the repository'' provides NRC with the flexibility 
to specify basic parameters, such as precipitation and temperature, 
that must be assumed by DOE, or to derive estimates of water flow 
directly. This is consistent with our current belief that the dominant 
mechanisms and flow paths for water to move from the surface through 
the repository and beyond should be determined by NRC rather than EPA. 
Further, we anticipated that ``constant climate conditions'' would be 
used as another parameter in the probabilistic assessment. That is, 
each realization would select its constant conditions from among a 
distribution of such conditions developed to reflect estimates of 
different future climate states. This is exactly the approach that NRC 
has taken in its proposal, i.e., that a range of deep percolation 
values be used (70 FR 53313-53320, September 8, 2005).
    Some commenters disagreed with the approach of specifying constant 
climate conditions leading to a higher rate of water flow through the 
repository, stating that the ``non-linear'' nature of the disposal 
system would be more sensitive to a dynamic, cyclical representation of 
climate. This is not necessarily true, as the effects on the disposal 
system would be highly affected by the timing of waste package failures 
(e.g., whether they fail during a wetter or drier cycle). Some comments 
cite recent climate research suggesting that anthropogenic climate 
influences will postpone the next glacial cycle by roughly 500,000 
years, or that today's climate at Yucca Mountain will actually be more 
representative of future climates than would the wetter conditions 
known to have occurred in the past. We believe that our final rule's 
approach to climate change provides a reasonable approach to address a 
point of fundamental uncertainty regarding long-term climate change and 
its role in the performance assessments, an uncertainty that cannot be 
removed by additional research into past climate cycles or modeling of 
present or future climate behavior. We refer to NAS on this point: 
``Although the typical nature of past climate changes is well known, it 
is obviously impossible to predict in detail either the nature or the 
timing of future climate change.'' (NAS Report p. 77, emphasis added) 
Although continuing research will provide better understanding of past 
climate fluctuations, we believe that predicting with high confidence 
the timing and extent of climate fluctuations into the far future will 
remain an unrealistic goal. We believe that the understanding of past 
climate fluctuations and their potential effects on the Yucca Mountain 
hydrologic system is valuable information and should be applied to 
define the climate-related parameter values. As noted above, NRC has 
used such information to propose climate-related parameter values, 
which DOE will use to project the behavior of hydrologic processes at 
the site. We believe that this approach to treatment of a ``residual, 
unquantifiable uncertainty'' by the application of ``informed 
judgment'' is consistent with NAS guidance. (NAS Report p. 80)

IV. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

    Under Executive Order 12866 (58 FR 51735, October 4, 1993), this 
action is a ``significant regulatory action'' because it raises novel 
legal or policy issues arising out of the specific legal mandate of 
section 801 of the Energy Policy Act of 1992. Accordingly, EPA 
submitted this action to the Office of Management and Budget for review 
under Executive Order 12866 and any changes made in response to OMB 
recommendations have been documented in the docket for this action.

B. Paperwork Reduction Act

    This action does not impose an information collection burden under 
the provisions of the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. 
Burden is defined at 5 CFR 1320.3(b). We have determined that this rule 
contains no information collection requirements within the scope of the 
Paperwork Reduction Act. This final rule establishes requirements that 
apply only to DOE.

C. Regulatory Flexibility Act

    The Regulatory Flexibility Act (RFA) generally requires an agency 
to prepare a regulatory flexibility analysis of any rule subject to 
notice and comment rulemaking requirements under the Administrative 
Procedure Act or any other statute unless the agency certifies that the 
rule will not have a significant economic impact on a substantial 
number of small entities. Small entities include small businesses, 
small organizations, and small governmental jurisdictions.
    For purposes of assessing the impacts of today's rule on small 
entities, small entity is defined as: (1) A small business as defined 
by the Small Business Administration's (SBA) regulations at 13 CFR 
121.201; (2) a small governmental jurisdiction that is a government of 
a city, county, town, school district or special district with a 
population of less than 50,000; and (3) a small organization that is 
any not-for-profit enterprise which is independently owned and operated 
and is not dominant in its field.
    After considering the economic impacts of today's final rule on 
small entities, I certify that this action will not have a significant 
economic impact upon a substantial number of small entities. This final 
rule will not impose any requirements on small entities. This final 
rule establishes requirements that apply only to DOE.

D. Unfunded Mandates Reform Act

    Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public 
Law 104-4, establishes requirements for Federal agencies to assess the 
effects of their regulatory actions on State, local, and tribal 
governments and the private sector. Under section 202 of the UMRA, EPA 
generally must prepare a written statement, including a cost-benefit 
analysis, for proposed and final rules with ``Federal mandates'' that 
may result in expenditures to State, local, and tribal governments, in 
the aggregate, or to the private sector, of $100 million or more in any 
one year. Before promulgating an EPA rule for which a written statement 
is needed, section 205 of the UMRA generally requires EPA to identify 
and consider a reasonable number of regulatory alternatives and adopt 
the least costly, most cost-effective or least burdensome alternative 
that achieves the objectives of the rule. The provisions of section 205 
do not apply when they are inconsistent with applicable law. Moreover, 
section 205 allows EPA to adopt an alternative other than the least 
costly, most cost-effective or least burdensome alternative if the 
Administrator publishes with the final rule an explanation why that 
alternative was not adopted. Before EPA establishes any regulatory 
requirements that may significantly or uniquely affect small 
governments, including tribal governments, it must have developed under 
section 203 of the UMRA a small government agency plan. The plan must 
provide for notifying potentially affected small governments, enabling 
officials of affected small governments to have meaningful and timely 
input in the development of EPA regulatory proposals with significant 
Federal intergovernmental mandates, and informing, educating, and 
advising small governments on compliance with the regulatory 
requirements.

[[Page 61286]]

    Today's final rule contains no Federal mandates (under the 
regulatory provisions of Title II of UMRA) for State, local, or tribal 
governments or the private sector. This final rule implements 
requirements specifically set forth by the Congress in section 801 of 
the EnPA and establishes radiological protection standards applicable 
solely and exclusively to the Department of Energy's potential storage 
and disposal facility at Yucca Mountain. The rule imposes no 
enforceable duty on any State, local or tribal governments or the 
private sector. Thus, today's rule is not subject to the requirements 
of sections 202 and 205 of UMRA.
    EPA has determined that this rule contains no regulatory 
requirements that might significantly or uniquely affect small 
governments. This final rule implements requirements specifically set 
forth by the Congress in section 801 of the EnPA and establishes 
radiological protection standards applicable solely and exclusively to 
the Department of Energy's potential storage and disposal facility at 
Yucca Mountain. The rule imposes no enforceable duty on any small 
governments. Thus, today's rule is not subject to the requirements of 
section 203 of UMRA.

E. Executive Order 13132: Federalism

    Executive Order 13132, entitled ``Federalism'' (64 FR 43255, August 
10, 1999), requires EPA to develop an accountable process to ensure 
``meaningful and timely input by State and local officials in the 
development of regulatory policies that have federalism implications.'' 
``Policies that have federalism implications'' is defined in the 
Executive Order to include regulations that have ``substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government.''
    This final rule does not have federalism implications. It will not 
have substantial direct effects on the States, on the relationship 
between the national government and the States, or on the distribution 
of power and responsibilities among the various levels of government, 
as specified in Executive Order 13132. This final rule implements 
requirements specifically set forth by the Congress in section 801 of 
the EnPA and establishes radiological protection standards applicable 
solely and exclusively to the Department of Energy's potential storage 
and disposal facility at Yucca Mountain. Thus, Executive Order 13132 
does not apply to this rule. In the spirit of Executive Order 13132, 
and consistent with EPA policy to promote communications between EPA 
and State and local governments, EPA specifically solicited comment on 
the proposed rule from State and local officials.

F. Executive Order 13175: Consultation and Coordination With Indian 
Tribal Governments

    Executive Order 13175, entitled ``Consultation and Coordination 
with Indian Tribal Governments'' (65 FR 67249, November 9, 2000), 
requires EPA to develop an accountable process to ensure ``meaningful 
and timely input by tribal officials in the development of regulatory 
policies that have tribal implications.'' This final rule does not have 
tribal implications, as specified in Executive Order 13175. This final 
rule will regulate only DOE on land owned by the Federal government. 
The rule does not have substantial direct effects on one or more Indian 
tribes, on the relationship between the Federal Government and Indian 
tribes, or on the distribution of power and responsibilities between 
the Federal Government and Indian tribes. Thus, Executive Order 13175 
does not apply to this rule.
    Although Executive Order 13175 does not apply to this rule, EPA 
specifically solicited additional comment on this proposed rule from 
tribal officials and consulted with tribal officials in developing this 
rule. EPA directly contacted more than 20 tribal governments and 
conducted three conference calls with members of tribal governments. In 
recognition of the importance of government-to-government consultation 
with tribes and the significance of tribal governments as sovereign 
nations, EPA extended the public comment period for tribal governments 
to December 31, 2005. Comments related to tribal issues, and our 
responses to them, may be found in Section 13 of the Response to 
Comments document associated with this final rule (docket ref).

G. Executive Order 13045: Protection of Children From Environmental 
Health & Safety Risks

    This final rule is not subject to Executive Order 13045 because it 
is not economically significant as defined in Executive Order 12866, 
and because the Agency does not have reason to believe the 
environmental health risks or safety risks addressed by this action 
present a disproportionate risk to children.

H. Executive Order 13211: Actions That Significantly Affect Energy 
Supply, Distribution, or Use

    This action is not a ``significant energy action'' as defined in 
Executive Order 13211 (66 FR 28355 (May 22, 2001)), because it is not 
likely to have a significant adverse effect on the supply, 
distribution, or use of energy. This final rule will apply only to DOE. 
Construction, operation, and closure of the repository at Yucca 
Mountain would fulfill the Federal government's commitment to manage 
the final disposition of spent nuclear fuel from commercial power 
reactors. However, there is no direct link between operation of the 
repository and an increased use of nuclear power. Other economic, 
technical, and policy factors will influence the extent to which 
nuclear energy is utilized.

I. National Technology Transfer and Advancement Act

    Section 12(d) of the National Technology Transfer and Advancement 
Act of 1995 (``NTTAA''), Public Law No. 104-113, 12(d) (15 U.S.C. 272 
note) directs EPA to use voluntary consensus standards in its 
regulatory activities unless to do so would be inconsistent with 
applicable law or otherwise impractical. Voluntary consensus standards 
are technical standards (e.g., materials specifications, test methods, 
sampling procedures, and business practices) that are developed or 
adopted by voluntary consensus standards bodies. NTTAA directs EPA to 
provide Congress, through OMB, explanations when the Agency decides not 
to use available and applicable voluntary consensus standards.
    This rulemaking involves technical standards. Therefore, the Agency 
conducted a search to identify potentially applicable voluntary 
consensus standards. In our original 1999 proposal (64 FR 46976), we 
requested public comment on potentially applicable voluntary consensus 
standards that would be appropriate for inclusion in the Yucca Mountain 
rule. However, we identified no such standards, and none were brought 
to our attention in comments. Therefore, the standards promulgated in 
2001 and today's final revisions are site-specific and developed solely 
for application to the Yucca Mountain disposal facility.

[[Page 61287]]

J. Executive Order 12898: Federal Actions To Address Environmental 
Justice in Minority Populations and Low-income Populations

    Executive Order (EO) 12898 (59 FR 7629 (Feb. 16, 1994)) establishes 
federal executive policy on environmental justice. Its main provision 
directs federal agencies, to the greatest extent practicable and 
permitted by law, to make environmental justice part of their mission 
by identifying and addressing, as appropriate, disproportionately high 
and adverse human health or environmental effects of their programs, 
policies, and activities on minority populations and low-income 
populations in the United States.
    EPA lacks the discretionary authority to address environmental 
justice in this final rulemaking. This final rule implements 
requirements specifically set forth by the Congress in section 801 of 
the EnPA and establishes radiological protection standards applicable 
solely and exclusively to the Department of Energy's potential storage 
and disposal facility at Yucca Mountain. Section 801(a)(1) of the EnPA 
directs EPA to ``promulgate, by rule, public health and safety 
standards'' that `` prescribe the maximum annual effective dose 
equivalent to individual members of the public'' from releases of 
radioactive material from the Yucca Mountain repository. This final 
rule fulfills this statutory direction.

K. Congressional Review Act

    The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the 
Small Business Regulatory Enforcement Fairness Act of 1996, generally 
provides that before a rule may take effect, the agency promulgating 
the rule must submit a rule report, which includes a copy of the rule, 
to each House of the Congress and to the Comptroller General of the 
United States. Section 804 exempts from section 801 the following types 
of rules: (1) Rules of particular applicability; (2) rules relating to 
agency management or personnel; and (3) rules of agency organization, 
procedure, or practice that do not substantially affect the rights or 
obligations of non-agency parties. 5 U.S.C. 804(3). EPA is not required 
to submit a rule report regarding today's action under section 801 
because this is a rule of particular applicability. This final rule 
will apply only to DOE, and is issued by EPA in response to direction 
from Congress in the EnPA.

List of Subjects in 40 CFR Part 197

    Environmental protection, Nuclear energy, Radiation protection, 
Radionuclides, Uranium, Waste treatment and disposal, Spent nuclear 
fuel, High-level radioactive waste.

    Dated: September 30, 2008.
Stephen L. Johnson,
Administrator.

0
40 CFR part 197 is amended as follows:

PART 197--PUBLIC HEALTH AND ENVIRONMENTAL RADIATION PROTECTION 
STANDARDS FOR YUCCA MOUNTAIN, NEVADA

0
1. The authority citation for part 197 continues to read as follows:

    Authority: Sec. 801, Pub. L. 102-486, 106 Stat. 2921, 42 U.S.C. 
10141n.

Subpart A--Public Health and Environmental Standards for Storage

0
2. Section 197.2 is amended by revising the definition of ``Effective 
dose equivalent'' to read as follows:


Sec.  197.2  What definitions apply in Subpart A?

* * * * *
    Effective dose equivalent means the sum of the products of the dose 
equivalent received by specified tissues following an exposure of, or 
an intake of radionuclides into, specified tissues of the body, 
multiplied by appropriate weighting factors. Annual committed effective 
dose equivalents shall be calculated using weighting factors in 
appendix A of this part, unless otherwise directed by NRC in accordance 
with the introduction to appendix A of this part.
* * * * *

Subpart B--Public Health and Environmental Standards for Disposal

0
3. Section 197.12 is amended by revising paragraph (1) of the 
definition of ``Performance assessment'' and the definition of ``Period 
of geologic stability'' to read as follows:


Sec.  197.12  What definitions apply in Subpart B?

* * * * *
    Performance assessment means an analysis that:
    (1) Identifies the features, events, processes, (except human 
intrusion), and sequences of events and processes (except human 
intrusion) that might affect the Yucca Mountain disposal system and 
their probabilities of occurring;
* * * * *
    Period of geologic stability means the time during which the 
variability of geologic characteristics and their future behavior in 
and around the Yucca Mountain site can be bounded, that is, they can be 
projected within a reasonable range of possibilities. This period is 
defined to end at 1 million years after disposal.
* * * * *

0
4. Section 197.13 is revised to read as follows:


Sec.  197.13  How is Subpart B implemented?

    The NRC implements this subpart B. The DOE must demonstrate to NRC 
that there is a reasonable expectation of compliance with this subpart 
before NRC may issue a license.
    (a) The NRC will determine compliance, based upon the arithmetic 
mean of the projected doses from DOE's performance assessments for the 
period within 1 million years after disposal, with:
    (1) Sections 197.20(a)(1) and 197.20(a)(2) of this subpart; and
    (2) Sections 197.25(b)(1), 197.25(b)(2), and 197.30 of this 
subpart, if performance assessment is used to demonstrate compliance 
with either or both of these sections.
    (b) [Reserved]

0
5. Section 197.15 is revised to read as follows:


Sec.  197.15  How must DOE take into account the changes that will 
occur during the period of geologic stability?

    The DOE should not project changes in society, the biosphere (other 
than climate), human biology, or increases or decreases of human 
knowledge or technology. In all analyses done to demonstrate compliance 
with this part, DOE must assume that all of those factors remain 
constant as they are at the time of license application submission to 
NRC. However, DOE must vary factors related to the geology, hydrology, 
and climate based upon cautious, but reasonable assumptions of the 
changes in these factors that could affect the Yucca Mountain disposal 
system during the period of geologic stability, consistent with the 
requirements for performance assessments specified at Sec.  197.36.

0
6. Section 197.20 is revised to read as follows:


Sec.  197.20  What standard must DOE meet?

    (a) The DOE must demonstrate, using performance assessment, that 
there is a reasonable expectation that the reasonably maximally exposed 
individual receives no more than the following annual committed 
effective dose equivalent from releases from the undisturbed Yucca 
Mountain disposal system:

[[Page 61288]]

    (1) 150 microsieverts (15 millirems) for 10,000 years following 
disposal; and
    (2) 1 millisievert (100 millirems) after 10,000 years, but within 
the period of geologic stability.
    (b) The DOE's performance assessment must include all potential 
pathways of radionuclide transport and exposure.

0
7. Section 197.25 is revised to read as follows:


Sec.  197.25  What standard must DOE meet?

    (a) The DOE must determine the earliest time after disposal that 
the waste package would degrade sufficiently that a human intrusion 
(see Sec.  197.26) could occur without recognition by the drillers.
    (b) The DOE must demonstrate that there is a reasonable expectation 
that the reasonably maximally exposed individual will receive an annual 
committed effective dose equivalent, as a result of the human 
intrusion, of no more than:
    (1) 150 microsieverts (15 millirems) for 10,000 years following 
disposal; and
    (2) 1 millisievert (100 millirems) after 10,000 years, but within 
the period of geologic stability.
    (c) The analysis must include all potential environmental pathways 
of radionuclide transport and exposure.

0
8. Section 197.35 is removed and reserved.


Sec.  197.35  [Removed and Reserved]

0
9. Section 197.36 is revised to read as follows:


Sec.  197.36  Are there limits on what DOE must consider in the 
performance assessments?

    (a) Yes, there are limits on what DOE must consider in the 
performance assessments.
    (1) The DOE's performance assessments conducted to show compliance 
with Sec. Sec.  197.20(a)(1), 197.25(b)(1), and 197.30 shall not 
include consideration of very unlikely features, events, or processes, 
i.e., those that are estimated to have less than one chance in 
100,000,000 per year of occurring. Features, events, and processes with 
a higher chance of occurring shall be considered for use in performance 
assessments conducted to show compliance with Sec. Sec.  197.20(a)(1), 
197.25(b)(1), and 197.30, except as stipulated in paragraph (b) of this 
section. In addition, unless otherwise specified in these standards or 
NRC regulations, DOE's performance assessments need not evaluate the 
impacts resulting from features, events, and processes or sequences of 
events and processes with a higher chance of occurring if the results 
of the performance assessments would not be changed significantly in 
the initial 10,000-year period after disposal.
    (2) The same features, events, and processes identified in 
paragraph (a)(1) of this section shall be used in performance 
assessments conducted to show compliance with Sec. Sec.  197.20(a)(2) 
and 197.25(b)(2), with additional considerations as stipulated in 
paragraph (c) of this section.
    (b) For performance assessments conducted to show compliance with 
Sec. Sec.  197.25(b) and 197.30, DOE's performance assessments shall 
exclude unlikely features, events, or processes, or sequences of events 
and processes. The DOE should use the specific probability of the 
unlikely features, events, and processes as specified by NRC.
    (c) For performance assessments conducted to show compliance with 
Sec. Sec.  197.20(a)(2) and 197.25(b)(2), DOE's performance assessments 
shall project the continued effects of the features, events, and 
processes included in paragraph (a) of this section beyond the 10,000-
year post-disposal period through the period of geologic stability. The 
DOE must evaluate all of the features, events, or processes included in 
paragraph (a) of this section, and also:
    (1) The DOE must assess the effects of seismic and igneous 
scenarios, subject to the probability limits in paragraph (a) of this 
section for very unlikely features, events, and processes. Performance 
assessments conducted to show compliance with Sec.  197.25(b)(2) are 
also subject to the probability limits for unlikely features, events, 
and processes as specified by NRC.
    (i) The seismic analysis may be limited to the effects caused by 
damage to the drifts in the repository, failure of the waste packages, 
and changes in the elevation of the water table under Yucca Mountain. 
NRC may determine the magnitude of the water table rise and its 
significance on the results of the performance assessment, or NRC may 
require DOE to demonstrate the magnitude of the water table rise and 
its significance in the license application. If NRC determines that the 
increased elevation of the water table does not significantly affect 
the results of the performance assessment, NRC may choose to not 
require its consideration in the performance assessment.
    (ii) The igneous analysis may be limited to the effects of a 
volcanic event directly intersecting the repository. The igneous event 
may be limited to that causing damage to the waste packages directly, 
causing releases of radionuclides to the biosphere, atmosphere, or 
ground water.
    (2) The DOE must assess the effects of climate change. The climate 
change analysis may be limited to the effects of increased water flow 
through the repository as a result of climate change, and the resulting 
transport and release of radionuclides to the accessible environment. 
The nature and degree of climate change may be represented by constant 
climate conditions. The analysis may commence at 10,000 years after 
disposal and shall extend through the period of geologic stability. The 
NRC shall specify in regulation the values to be used to represent 
climate change, such as temperature, precipitation, or infiltration 
rate of water.
    (3) The DOE must assess the effects of general corrosion on 
engineered barriers. The DOE may use a constant representative 
corrosion rate throughout the period of geologic stability or a 
distribution of corrosion rates correlated to other repository 
parameters.

0
10. Appendix A to part 197 is added to read as follows:

Appendix A to Part 197--Calculation of Annual Committed Effective Dose 
Equivalent

    Unless otherwise directed by NRC, DOE shall use the radiation 
weighting factors and tissue weighting factors in this Appendix to 
calculate the internal component of the annual committed effective 
dose equivalent for compliance with Sec. Sec.  197.20 and 197.25 of 
this part. NRC may allow DOE to use updated factors issued after the 
effective date of this regulation. Any such factors shall have been 
issued by consensus scientific organizations and incorporated by EPA 
into Federal radiation guidance in order to be considered generally 
accepted and eligible for this use. Further, they must be compatible 
with the effective dose equivalent dose calculation methodology 
established in ICRP 26 and 30, and continued in ICRP 60 and 72, and 
incorporated in this appendix.

I. Equivalent Dose

    The calculation of the committed effective dose equivalent 
(CEDE) begins with the determination of the equivalent dose, 
HT, to a tissue or organ, T, listed in Table A.2 below by 
using the equation:
[GRAPHIC] [TIFF OMITTED] TR15OC08.000

where DT,R is the absorbed dose in rads (one gray, an SI 
unit, equals 100 rads) averaged over the tissue or organ, T, due to 
radiation type, R, and wR is the radiation weighting 
factor which is given in Table A.1 below. The unit of equivalent 
dose is the rem (sievert, in SI units).

[[Page 61289]]



               Table A.1--Radiation weighting factors, wR1
------------------------------------------------------------------------
            Radiation type and energy range \2\                wR value
------------------------------------------------------------------------
Photons, all energies......................................            1
Electrons and muons, all energies..........................            1
Neutrons, energy
    < 10 keV...............................................            5
    10 keV to 100 keV......................................           10
    > 100 keV to 2 MeV.....................................           20
    >2 MeV to 20 MeV.......................................           10
    > 20 MeV...............................................            5
Protons, other than recoil protons, > 2 MeV................            5
Alpha particles, fission fragments, heavy nuclei...........          20
------------------------------------------------------------------------
\1\ All values relate to the radiation incident on the body or, for
  internal sources, emitted from the source.
\2\ See paragraph A14 in ICRP Publication 60 for the choice of values
  for other radiation types and energies not in the table.

II. Effective Dose Equivalent

    The next step is the calculation of the effective dose 
equivalent, E. The probability of occurrence of a stochastic effect 
in a tissue or organ is assumed to be proportional to the equivalent 
dose in the tissue or organ. The constant of proportionality differs 
for the various tissues of the body, but in assessing health 
detriment the total risk is required. This is taken into account 
using the tissue weighting factors, wT in Table A.2, 
which represent the proportion of the stochastic risk resulting from 
irradiation of the tissue or organ to the total risk when the whole 
body is irradiated uniformly and HT is the equivalent 
dose in the tissue or organ, T, in the equation:
[GRAPHIC] [TIFF OMITTED] TR15OC08.001


                 Table A.2--Tissue weighting factors, wT
------------------------------------------------------------------------
                      Tissue or organ                          wT value
------------------------------------------------------------------------
Gonads.....................................................         0.20
Bone marrow (red)..........................................         0.12
Colon......................................................         0.12
Lung.......................................................         0.12
Stomach....................................................         0.12
Bladder....................................................         0.05
Breast.....................................................         0.05
Liver......................................................         0.05
Esophagus..................................................         0.05
Thyroid....................................................         0.05
Skin.......................................................         0.01
Bone surface...............................................         0.01
Remainder..................................................    a b 0.05
------------------------------------------------------------------------
\a\ Remainder is composed of the following tissues: adrenals, brain,
  extrathoracic airways, small intestine, kidneys, muscle, pancreas,
  spleen, thymus, and uterus.
\b\ The value 0.05 is applied to the mass-weighted average dose to the
  Remainder tissues group, except when the following ``splitting rule''
  applies: If a tissue of Remainder receives a dose in excess of that
  received by any of the 12 tissues for which weighting factors are
  specified, a weighting factor of 0.025 (half of Remainder) is applied
  to that tissue or organ and 0.025 to the mass-averaged committed
  equivalent dose equivalent in the rest of the Remainder tissues.

III. Annual Committed Tissue or Organ Equivalent Dose

    For internal irradiation from incorporated radionuclides, the 
total absorbed dose will be spread out in time, being gradually 
delivered as the radionuclide decays. The time distribution of the 
absorbed dose rate will vary with the radionuclide, its form, the 
mode of intake and the tissue within which it is incorporated. To 
take account of this distribution the quantity committed equivalent 
dose, HT([tau]) where [tau] is the integration time in 
years following an intake over any particular year, is used and is 
the integral over time of the equivalent dose rate in a particular 
tissue or organ that will be received by an individual following an 
intake of radioactive material into the body:
[GRAPHIC] [TIFF OMITTED] TR15OC08.002

for a single intake of activity at time t0 where 
HT([tau]) is the relevant equivalent-dose rate in a 
tissue or organ at time t. For the purposes of this rule, the 
previously mentioned single intake may be considered to be an annual 
intake.

IV. Internal Component of the Annual Committed Effective Dose 
Equivalent

    If the annual committed equivalent doses to the individual 
tissues or organs resulting from an annual intake are multiplied by 
the appropriate weighting factors, wT, from table A.2, 
and then summed, the result will be the internal component of the 
annual committed effective dose equivalent E([tau]):
[GRAPHIC] [TIFF OMITTED] TR15OC08.003

[FR Doc. E8-23754 Filed 10-14-08; 8:45 am]

BILLING CODE 6560-50-P
