[Federal Register Volume 74, Number 48 (Friday, March 13, 2009)]
[Rules and Regulations]
[Pages 10811-10830]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E9-5448]



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Federal Register / Vol. 74, No. 48 / Friday, March 13, 2009 / Rules 
and Regulations

[[Page 10811]]



NUCLEAR REGULATORY COMMISSION

10 CFR Part 63

RIN 3150-AH68
[NRC-2005-0011]


Implementation of a Dose Standard After 10,000 Years

AGENCY: Nuclear Regulatory Commission.

ACTION: Final rule.

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

SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is amending its 
regulations governing the disposal of high-level radioactive wastes in 
a proposed geologic repository at Yucca Mountain, Nevada. The final 
rule implements the U.S. Environmental Protection Agency's (EPA's) 
revised standards for doses that could occur after 10,000 years, but 
within the period of geologic stability. The final rule also specifies 
a range of values for the deep percolation rate to be used to represent 
climate change after 10,000 years, as called for by EPA, and specifies 
that calculations of radiation doses for workers use the same weighting 
factors that EPA is using for calculating individual doses to members 
of the public.

DATES: Effective Date: This final rule is effective on April 13, 2009.

ADDRESSES: Publicly available documents related to this rulemaking may 
be viewed electronically on the public computers located at the NRC's 
Public Document Room (PDR), Room O1F21, One White Flint North, 11555 
Rockville Pike, Rockville, Maryland. The PDR reproduction contractor 
will copy documents for a fee. Selected documents and information on 
this rulemaking can be accessed at the Federal rulemaking portal, 
http://regulations.gov by searching on rulemaking docket ID: NRC-2005-
0011.
    Publicly available documents created or received at the NRC are 
available electronically at the NRC's Electronic Reading Room at http://www.nrc.gov/reading-rm/adams.html. From this site, the public can gain 
entry into the NRC's Agencywide Document Access and Management System 
(ADAMS), which provides text and image files of NRC's public documents. 
If you do not have access to ADAMS or if there are problems in 
accessing the documents located in ADAMS, contact the NRC Public 
Document Room (PDR) Reference staff at (800) 397-4209, (301) 415-4737, 
or by e-mail to <a href="/cdn-cgi/l/email-protection#e3938791cd9186908c96918086a38d9180cd848c95"><span class="__cf_email__" data-cfemail="215145530f5344524e54534244614f53420f464e57">[email protected]</span></a>.

FOR FURTHER INFORMATION CONTACT: Timothy McCartin, Office of Nuclear 
Material Safety and Safeguards, U.S. Nuclear Regulatory Commission, 
Washington, DC 20555-0001, telephone (301) 492-3167, e-mail 
<a href="/cdn-cgi/l/email-protection#e3b78a8e8c978b9acdae80a08291978a8da38d9180cd848c95"><span class="__cf_email__" data-cfemail="c591aca8aab1adbceb88a686a4b7b1acab85abb7a6eba2aab3">[email protected]</span></a>; Janet Kotra, Office of Nuclear Material 
Safety and Safeguards, U.S. Nuclear Regulatory Commission, Washington, 
DC 20555-0001, telephone (301) 492-3190, e-mail <a href="/cdn-cgi/l/email-protection#de94bfb0bbaaf095b1aaacbf9eb0acbdf0b9b1a8"><span class="__cf_email__" data-cfemail="5f153e313a2b7114302b2d3e1f312d3c71383029">[email protected]</span></a>; or 
Robert MacDougall, Office of Federal and State Materials and 
Environmental Management Programs, U.S. Nuclear Regulatory Commission, 
Washington, DC 20555-0001, telephone (301) 415-5175, e-mail 
<a href="/cdn-cgi/l/email-protection#f7a59895928583d9ba9694b3988290969b9bb7998594d9909881"><span class="__cf_email__" data-cfemail="5d0f323f382f2973103c3e1932283a3c31311d332f3e733a322b">[email protected]</span></a>.

SUPPLEMENTARY INFORMATION:

I. Background
II. Implementation of the Environmental Protection Agency's Final 
Standards for a Compliance Period Beyond 10,000 Years and Within the 
Period of Geologic Stability
III. Public Comments and Responses
    1. NRC Adoption of EPA Standards
    2. Clarifications on NRC's Implementation of Features, Events, 
and Processes for the Performance Assessment for the Period After 
10,000 Years
    3. Climate Change
    4. Use of Current Dosimetry
    5. Comments Beyond the Scope of This Rulemaking
IV. Summary of Final Revisions
V. Agreement State Compatibility
VI. Voluntary Consensus Standards
VII. Finding of No Significant Environmental Impact: Availability
VIII. Paperwork Reduction Act Statement
IX. Regulatory Analysis
X. Regulatory Flexibility Certification
XI. Backfit Analysis
XII. Congressional Review Act

I. Background

    On November 2, 2001 (66 FR 55732), NRC published its final rule, 10 
CFR Part 63, governing disposal of high-level radioactive wastes in a 
potential geologic repository at Yucca Mountain, Nevada. The U.S. 
Department of Energy (DOE) must comply with these regulations for NRC 
to authorize construction and license operation of a potential 
repository at Yucca Mountain. As mandated by the Energy Policy Act of 
1992 (EnPA), Public Law 102-486, NRC's final rule was consistent with 
the radiation protection standards issued by EPA at 40 CFR Part 197 (66 
FR 32074; June 13, 2001). EPA developed these standards pursuant to 
Congress' direction, in Section 801 of EnPA, to issue public health and 
safety standards for protection of the public from releases of 
radioactive materials stored or disposed of in a potential repository 
at the Yucca Mountain site. Such standards were to be ``based upon and 
consistent with'' the findings and recommendations of the National 
Academy of Sciences (NAS). The NAS issued its findings and 
recommendations, on August 1, 1995, in a report entitled Technical 
Bases for Yucca Mountain Standards.
    The State of Nevada and other petitioners challenged both the EPA 
standards and the NRC regulations in court. On July 9, 2004, the United 
States Court of Appeals for the District of Columbia Circuit upheld 
both EPA's standards and NRC's regulations on all but one of the issues 
raised by the petitioners. See Nuclear Energy Institute, Inc. v. 
Environmental Protection Agency, 373 F.3d 1251 (DC Cir. 2004) (NEI v. 
EPA). The court disagreed with EPA's decision to adopt a 10,000-year 
period for compliance with the standards and NRC's adoption of that 
10,000-year compliance period in NRC's implementing regulations. The 
court found that EPA's 10,000-year compliance period was not ``* * * 
based upon and consistent with'' NAS' findings, as required by Section 
801 of EnPA. See 373 F.3d at 1270. The NAS recommended EPA develop 
standards that provide protection when radiation doses reach their 
peak, within the limits imposed by long-term stability of the geologic 
environment. In addition, NAS found no scientific basis for limiting 
application of the individual-risk standard to 10,000 years. Thus, the

[[Page 10812]]

court vacated EPA's rule, at 40 CFR Part 197, to the extent that it 
specified a 10,000-year compliance period, and remanded the matter to 
EPA. The court also vacated NRC's rule, at 10 CFR Part 63, insofar as 
it incorporated EPA's 10,000-year compliance period.

EPA's Proposed Rule

    In response to the remand, EPA proposed revisions (70 FR 49014; 
August 22, 2005) to elements of its standards affected by the court's 
decision. EPA proposed to revise its individual-protection and human-
intrusion standards to incorporate the time of peak dose into the 
determination of compliance. EPA retained its 0.15 millisievert (mSv)/
year [15 millirem (mrem)/year] standards for 10,000 years after 
disposal, and added a 3.5 mSv (350 mrem) standard for the period after 
10,000 years, but within the period of geologic stability. EPA defined 
the period of geologic stability as ending at 1 million years after 
disposal. Further, EPA proposed that NRC base its determination of 
compliance with the post-10,000 year standards, based on the median of 
the projected doses from DOE's performance assessments, rather than on 
the arithmetic mean of the projected doses. The arithmetic mean was 
still retained as the compliance measure for the first 10,000 years 
after disposal.
    EPA also proposed to define how DOE should incorporate features, 
events, and processes (FEPs) in the performance assessment for the 
period after 10,000 years. EPA explained that the goal of the 
performance assessment ``is to design an assessment that is a 
reasonable test of the disposal system under a range of conditions that 
represents the expected case, as well as relatively less likely (but 
not wholly speculative) scenarios with potentially significant 
consequences. The challenge is to define the parameters of the 
assessment so that they demonstrate whether or not the disposal system 
is resilient and safe in response to meaningful disruptions, while 
avoiding extremely speculative (and in some cases, fantastical) 
events.'' (70 FR 49048; August 22, 2005). EPA proposed that DOE's 
performance assessments conducted to show compliance with the post-
10,000 year individual protection and human-intrusion standards shall 
project the continued effects of the FEPs included in the initial 
10,000 year analysis. EPA also proposed certain constraints on DOE's 
performance assessments for the post-10,000 year period. These are:
    (1) Seismic analysis may be limited to the effects caused by damage 
to the drifts in the repository and the failure of the waste packages;
    (2) Igneous analysis may be limited to the effects of a volcanic 
activity event directly intersecting the repository, and 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;
    (3) Climate change analysis may be limited to the effects of 
increased water flow through the repository as a result of climate 
change, and that the nature and degree of climate change may be 
represented by sampling within a range of specified constant 
conditions; and
    (4) DOE must assess the effects of general corrosion on engineered 
barriers and may use a constant representative corrosion rate 
throughout the period of geologic stability, or a distribution of 
corrosion rates correlated to other repository parameters.
    With respect to climate change, EPA further proposed that NRC shall 
specify in regulation the values to be used to represent climate 
change, such as temperature, precipitation, or infiltration rate of 
water.
    Finally, in its definition of ``effective dose equivalent'' EPA 
proposed that DOE calculate annual committed effective dose equivalents 
using the weighting factors that would be incorporated in its 
regulations in a new Appendix A to 40 CFR Part 197. EPA believes this 
reflects the most recent application of current radiation science to 
the calculation of dose.

NRC's Proposed Rule

    Under the EnPA, NRC's regulations must be consistent with EPA's 
standards. On September 8, 2005, NRC proposed revisions to its 
regulations designed to achieve consistency with EPA's proposed revised 
standards (70 FR 53313; September 8, 2005). NRC proposed to incorporate 
the new post-10,000 year dose limit of 3.5 mSv/year (350 mrem/year) and 
statistical measure for compliance directly into its regulations for 
individual protection and human intrusion. Also, NRC proposed to adopt 
specific constraints EPA proposed for considering FEPs after 10,000 
years. NRC proposed to revise its requirements to be consistent with 
EPA's proposal that the performance assessment for the first 10,000 
years serve as the basis for projecting repository performance after 
10,000 years. NRC, supporting the use of current dosimetry, proposed to 
adopt the specific weighting factors provided in Appendix A of 40 CFR 
Part 197. Overall, NRC's proposed changes to Part 63 adopted the same 
or approximately the same wording as used by EPA in its proposed 
revisions to 40 CFR Part 197. Further, consistent with EPA's 
specification of dosimetry for calculating individual doses to members 
of the public, NRC proposed to revise its Part 63 regulations to allow 
DOE to use the same methods for calculating doses to workers during the 
operational period. Finally, in response to EPA's proposal, NRC 
proposed to specify, in its regulation, steady-state (constant-in-time) 
values that DOE should use to project the long-term impact of climate 
variation. NRC proposed that DOE represent future climate change in the 
performance assessment by sampling constant-in-time deep percolation 
rates from a log-uniform distribution, which varies between 13 and 64 
millimeters (mm)/year [0.5 and 2.5 inches (in.)/year].
    NRC's notice of proposed rulemaking invited comments on its 
proposal to implement EPA's proposed revisions to its standards, as 
well as on NRC's revisions for use of specific weighting factors for 
calculating worker doses, and on NRC's specification of values for 
climate change. NRC requested comments only on those provisions of Part 
63 that NRC proposed to change and noted that its existing regulations 
were not affected by this rulemaking except insofar as NRC's proposed 
rule adopts more up-to-date dosimetry for dose calculations. NRC 
notified potential commenters that comments on EPA's revised standards 
should be directed to EPA. In response to requests from the public, NRC 
extended the comment period, originally ending on November 7, 2005, to 
December 7, 2005 (70 FR 67098; November 4, 2005).

II. Implementation of the Environmental Protection Agency's Final 
Standards for a Compliance Period Beyond 10,000 Years and Within the 
Period of Geologic Stability

EPA's Final Rule

    EPA published final ``Public Health and Environmental Radiation 
Protection Standards for Yucca Mountain, Nevada,'' for the period after 
10,000 years at 40 CFR Part 197 on October 15, 2008 (73 FR 61256). EPA 
has finalized its proposals relating to: consideration of FEPs in the 
post-10,000 year period, and use of specific weighting factors that 
reflect current methods of dosimetry and updated models for calculating 
individual exposures from radiation. EPA's final rule differs from its 
proposal in two respects: the dose limit and the consideration of 
seismic activity.

[[Page 10813]]

    First, the EPA standards establish a 1.0 mSv/year (100 mrem/year) 
dose limit for the reasonably maximally exposed individual (RMEI) for 
the period after 10,000 years and within the period of geologic 
stability, rather than a 3.5 mSv/year (350 mrem/year) dose limit, as 
had been proposed. The EPA standards also provide that NRC base its 
determination of compliance with the post-10,000 year standards on the 
arithmetic mean of the projected doses, rather than on the median, as 
was proposed.
    Second, EPA's standards now require that analyses of seismic 
activity consider water table rise under Yucca Mountain caused by 
seismic activity. The final standards specify that NRC may determine 
the magnitude of the water table rise to be used in the performance 
assessment for the period after 10,000 years or, if this magnitude is 
found to be insignificant, not require its consideration in performance 
assessment. Alternatively, NRC may require DOE to demonstrate the 
magnitude of the water table rise and its significance in terms of 
repository performance in its license application.

NRC's Final Rule

    EnPA directs the Commission to modify its technical criteria to be 
consistent with EPA's standards for a geologic repository at the Yucca 
Mountain site. NRC's final rule achieves this consistency by 
incorporating the revised standards into its final revised 10 CFR Part 
63 regulations as transparently as possible. A brief description of the 
Commission's implementation of EPA's standards follows:
    (1) For the period after 10,000 years and within the period of 
geologic stability (up to 1 million years), NRC adopts EPA's 1.0 mSv/
year (100 mrem/year) dose limit for the RMEI in both the individual 
protection standard at 10 CFR 63.311 and the human intrusion standard 
at 10 CFR 63.321.
    (2) NRC adopts, in 10 CFR 63.303, EPA's specification of the 
arithmetic mean as the basis for determining compliance with the dose 
limit for the post-10,000-year period.
    (3) NRC adopts, in 10 CFR 63.305 and 63.342, EPA's specific 
requirements for the performance assessment DOE must use to evaluate 
the behavior of the repository for the period after 10,000 years. The 
FEPs selected for use in the performance assessment for the first 
10,000 years should also be used for projecting repository performance 
after 10,000 years. NRC adopts EPA's additional constraints for the 
inclusion of seismic activity, igneous activity, climate change, and 
general corrosion in the performance assessment for the period of time 
after 10,000 years. The seismic analysis must include the magnitude of 
the water table rise and its significance on the results of the 
performance assessment unless NRC, through rulemaking, decides to 
specify the magnitude of the water table rise to be used in the 
performance assessment after 10,000 years or to not require its 
consideration.
    (4) NRC adopts, in 10 CFR 63.102(o), EPA's specification of the 
weighting factors to be used for estimating potential radiation 
exposures for members of the public, which are provided in Appendix A 
of 40 CFR Part 197.
    In addition to the changes made for consistency with EPA's 
standards, NRC proposed to add a definition for ``weighting factor'' 
and to amend Sec.  63.111(a)(1) to allow DOE to use the weighting 
factors in Appendix A for calculating doses to workers. After 
consideration of the public comments, NRC chooses not to add the 
proposed definition for ``weighting factor'' to its regulations nor to 
amend Sec.  63.111(a)(1). Instead, NRC is providing a discussion 
regarding implementation of total effective dose equivalent (TEDE). NRC 
is adding text at Sec.  63.102(o) to clarify that the weighting factors 
specified in EPA's final standards should be used for dose calculations 
for workers and the public. Thus, TEDE calculations of potential 
radiation exposures to workers and the public are implemented 
consistently with a single set of weighting factors based on current 
dosimetry. The definition for TEDE is also revised to be consistent 
with NRC regulations at Part 20. This approach avoids the unnecessary 
complication and potential confusion that could result from the use of 
different definitions in Parts 20 and 63 and provides a single, clear 
statement on the proper implementation of TEDE in Part 63 thereby 
eliminating any need for further changes. (See response to comments 
under Use of Current Dosimetry, in this document.)
    EPA's rule requires DOE to assess the effects of climate change in 
the period after 10,000 years. This assessment is limited to the 
effects of increased water flow through the repository. The nature and 
degree of climate change may be represented by sampling within a range 
of constant climate conditions. EPA leaves it to NRC to specify, in 
regulation, the values to be used to represent climate change, such as 
temperature, precipitation, or infiltration of water. NRC's proposed 
rule sought public comment on its approach for representing the effect 
of future climate in performance assessments after 10,000 years. NRC 
proposed that the constant value to be used to represent climate change 
is to be sampled from a log-uniform distribution for deep percolation 
rates, which varies between 13 and 64 mm/year (0.5 and 2.5 in./year).
    After consideration of the public comments received on its 
proposal, NRC's final rule adopts its proposed approach with some 
modifications. NRC will require that DOE represent the effects of 
climate change by assuming constant-in-time climate conditions. The 
analysis may commence for the period beginning at 10,000 years after 
disposal and shall extend through the period of geologic stability. The 
constant-in-time value to be used to represent climate change is to be 
the spatial average of the deep percolation rate within the area 
bounded by the repository footprint. The constant-in-time deep 
percolation rates to be used now to represent climate change shall be 
sampled from a ``truncated'' lognormal distribution for deep 
percolation rates, which varies between 10 and 100 mm/year (0.39 and 
3.9 in./year). This ``truncated'' lognormal distribution has an 
arithmetic mean of 37 mm/year (1.5 in./year) for the deep percolation 
rate as compared to an arithmetic mean of 32 mm/year (1.3 in./year) 
based on the range and distribution in the proposed regulations. (See 
response to comments under Climate Change, in this document for further 
details on this approach and the consideration of public comments.)
    For a full description of changes NRC is incorporating into its 
Part 63 regulations, see Section IV of this document.

Water Table Rise From Seismic Activity

    NRC currently requires DOE to demonstrate the magnitude of the 
water table rise from seismic activity and its significance in its 
license application. The National Research Council (1992) conducted a 
comprehensive technical evaluation of mechanisms that could raise the 
water table at Yucca Mountain (National Research Council, Ground Water 
at Yucca Mountain: How High Can It Rise?, National Academy Press, 
Washington, DC, 1992). The Council considered both the dynamic response 
of the water table to propagation of seismic waves, as well as the 
long-term hydrologic response of the ground water system to permanent 
changes in rock stress after the seismic waves pass. The Council 
concluded that transient effects are not relevant to the performance of 
a repository. Of potential significance, however, are permanent changes 
to the

[[Page 10814]]

fluid pore pressure or rock permeability that may bring about long-term 
changes in the height of the water table. The report's authors 
evaluated historical accounts of relevant large earthquakes that have 
caused long-term changes to the regional hydrologic regime of ground 
water systems. The authors conducted site-specific quantitative 
analyses of the potential change in the level of the water table. They 
concluded that ``although the models are based on very limited data * * 
* [the] stress/strain changes resulting from an earthquake are 
inadequate to cause more than a few tens of meters rise in the water 
table based on the convergence of the results by a variety of models 
and assumptions, especially if the deep carbonate aquifer is as 
incompressible as the limited data suggest.'' Whatever approach DOE 
takes when determining the magnitude of the water table rise from 
seismic activity, NRC expects that DOE will consider the information 
provided by the National Research Council as referenced in the National 
Academy of Sciences report entitled, ``Technical Bases for Yucca 
Mountain Standards'' (1995) at page 94 (i.e., ``Results indicate a 
probable maximum transient rise on the order of 20 m or less'').
    Although EPA standards specify that NRC may determine the magnitude 
of water table rise and its significance, NRC is not planning such 
action. If, in the future, NRC decides to specify the magnitude of the 
water table rise and whether it is significant enough for consideration 
in DOE's performance assessment, NRC will do so in a future rulemaking.

III. Public Comments and Responses

    The NRC received 16 individual comment submittals, many of which 
contained numerous specific comments. In addition, NRC received more 
than 3000 submissions objecting, in nearly identical text, to NRC's 
adoption of EPA's standards because the commenters believed the 
proposed standards are inadequate and because NRC published its 
proposed revision to Part 63 before EPA issued final standards. NRC 
carefully reviewed and considered the range of comments received during 
the public comment period. The NRC staff grouped the comments into the 
following five major topic areas:
    (1) NRC Adoption of EPA Standards;
    (2) Clarifications on NRC's Implementation of FEPs for the 
Performance Assessment for the Period after 10,000 Years;
    (3) Climate Change;
    (4) Use of Current Dosimetry; and
    (5) Comments Beyond the Scope of this Rulemaking.

1. NRC Adoption of EPA Standards

    Issue 1: Must NRC supplement EPA's standards because they do not 
adequately protect public health and safety and the environment?
    Comment. Some commenters supported NRC's adoption of EPA's 
standards, while others opposed adoption because they believe EPA's 
proposed standards are inadequate to protect public health and safety 
and the environment. The State of Nevada recognized that EnPA requires 
NRC's regulations to be consistent with EPA's standards but claims this 
does not mean the two must be identical. Rather, the State asserts, NRC 
must recognize that compliance with EPA's standards is necessary but 
not sufficient to provide adequate protection of public health and 
safety and the environment. The State also asserts that NRC should 
promulgate supplemental standards, in its regulations, that will 
provide the additional protection the State believes is needed. With 
respect to EPA's proposed standards, the State and other commenters 
particularly objected to EPA's 3.5 mSv/year (350 mrem/year) post-10,000 
year standard and use of the median to assess compliance. The State and 
other commenters also objected to many other features of the EPA 
standards, including limitations on the FEPs, use of a two-tier 
standard, and defining the period of geologic stability as ending at 1 
million years. In support of its comments, the State attached a copy of 
the comments on the EPA proposed standards it had submitted to EPA.
    Response. While EnPA does not require NRC regulations to be 
identical to EPA's, EnPA does direct the Commission to modify its 
technical criteria to be consistent with EPA's standards for a geologic 
repository at the Yucca Mountain site. Thus, NRC is required to adopt 
EPA's post 10,000 year standard, and the NRC has done so. The NRC's 
notice of proposed rulemaking notified potential commenters that 
comments such as these on EPA's revised standards should be directed to 
EPA for EPA's response.
    Issue 2: Should NRC extend the compliance period beyond 1 million 
years if it is determined that the peak dose may occur beyond the 1 
million-year period?
    Comment. The State commented that EPA's requirement that the post-
10,000 year performance assessment should end at 1 million years is 
unnecessarily prescriptive. The State believes that if the trends in 
dose projection are not clear or heading upward and geologic stability 
is maintained, extending the assessment beyond 1 million years may be 
required to establish the performance of the entire repository system. 
The State believes that NRC has the authority to consider not only the 
magnitude of the peak, but also the timing and overall trends of dose 
projections as it evaluates the license application.
    Response. As explained in the response to the comment on Issue 1 
under NRC Adoption of EPA Standards of this document, EnPA requires the 
Commission to modify its technical criteria to be consistent with EPA's 
standards for a geologic repository at the Yucca Mountain site. The 
NRC's notice of proposed rulemaking notified potential commenters that 
comments such as these on EPA's revised standards should be directed to 
EPA for EPA's response.
    Issue 3: Has NRC illegitimately used rulemaking to resolve issues 
that must be resolved in an adjudicatory proceeding?
    Comment. The State of Nevada commented that the proposed rule 
violates fundamental principles of administrative law because it fails 
to conform to the usual distinctions in agency administrative processes 
between ``rulemaking'' and ``adjudication.'' This is because the rule 
includes what the commenter believes to be ``determinations of 
adjudicative fact'' that apply only to Yucca Mountain and that should 
be matters adjudicated in NRC's hearing on DOE's license application. 
According to the commenter, there are two critical distinctions between 
rulemaking and adjudication: ``First, a rule addresses the future while 
an order [the product of adjudication] addresses the past or the 
present. Second, a rule is based on general policy considerations or on 
what are sometimes called legislative facts, generalizations about 
people and things, while an order is based on specific facts about 
things and individuals, sometimes called adjudicative facts.'' The 
commenter believes that the proposed rule violates this distinction 
because ``[n]o agency may resolve a controversy over an adjudicative 
fact, relevant only to a single adjudication, by rulemaking.'' The 
State further asserts that NRC's alleged improper use of rulemaking to 
resolve adjudicatory factual issues constitutes an unlawful abrogation 
of Nevada's right, under section 189 of the Atomic Energy Act of 1954 
as amended (AEA), to an NRC licensing hearing on these factual issues.

[[Page 10815]]

    In the State's view, NRC cannot claim that it is permitted to 
resolve adjudicatory factual issues in its rulemaking simply because 
EPA did so and NRC must adopt EPA's standards. The commenter recognizes 
that the EnPA alters a straightforward demarcation between rulemaking 
and adjudication because ``EnPA does contemplate Yucca `rules' that by 
their nature depend on some facts relevant only to Yucca.'' However, 
the commenter contends that ``EnPA authorized only those EPA findings 
of adjudicatory fact that (1) are based on what the [National] Academy 
[of Sciences] considered necessary to support an EPA rule; and (2) are 
essential to promulgate limits on radiation exposures, concentrations, 
or quantities beyond the boundary of the Yucca Mountain site.'' This is 
because the grant of authority to EPA in EnPA to issue standards 
applicable only to Yucca Mountain is based on the previous delegation 
of rulemaking authority to EPA in section 121 of the Nuclear Waste 
Policy Act of 1982 (NWPA), which, in turn, relies upon the delegation 
of authorities to EPA in Reorganization Plan Number 3 of 1970 that 
identifies what standards EPA may issue. The commenter believes that 
the EPA standards that NRC is adopting are rife with ``adjudicative 
facts'' and go well beyond the narrow limits permitted by EnPA.
    The commenter cites eight ``determinations of adjudicative fact'' 
that appear in NRC's proposed rule, most of which NRC is adopting from 
EPA's standards:
    (1) The performance assessment for the period after 10,000 years 
must use a time-independent log-uniform probability distribution for 
deep percolation rates of from 13 to 64 mm/year;
    (2) Models and data used to develop FEPs (``features, events and 
processes'') for the assessment period before 10,000 years are 
sufficient for the post-10,000-year assessment period;
    (3) Seismic analyses for the post-10,000 year period may be based 
on seismic hazard curves developed for the pre-10,000-year period;
    (4) Seismic effects in the post-10,000-year period may be limited 
to effects on the repository's drifts and waste packages;
    (5) Igneous effects in the post-10,000 year period may be limited 
to effects on waste packages;
    (6) The effects of climate change in the post-10,000-year period 
may be limited to increased water flux through the repository;
    (7) Different types of corrosion of the waste packages must be 
considered in the pre-10,000-year period but only general corrosion at 
a constant rate may be considered in the post-10,000-year period; \1\ 
and
---------------------------------------------------------------------------

    \1\ The rule does not, in fact, restrict consideration of 
corrosion in the post-10,000 year period to general corrosion; other 
types of corrosion, if important, will be carried over from the pre-
10,000 year period and will also be considered.
---------------------------------------------------------------------------

    (8) Effects of climate change in the post-10,000-year period may be 
expressed by steady state (time independent) values.
    Response. The Commission disagrees with the comment. ``It is a 
well-settled principle of administrative law that the decision whether 
to proceed by rulemaking or adjudication lies within the broad 
discretion of the agency. See, SEC v. Chenery Corp., 332 U.S. 194, 202-
03 (1947)'' Wisconsin Gas Company v. Federal Energy Regulatory 
Commission, 770 F.2d 1144, 1166 (DC Cir. 1985). The Commission has 
properly exercised its discretion to resolve the issues referenced by 
the commenter through rulemaking rather than through adjudication.
    The commenter mischaracterizes as ``determinations of adjudicative 
fact'' what are in reality assumptions, derived from data, testing, and 
scientific analysis, that DOE is to use in its performance assessment 
to demonstrate compliance with regulatory standards. A performance 
assessment is used to take account of the considerable uncertainties 
inherent in projecting disposal system performance over times as long 
as 1 million years. The performance assessment is not intended to 
resolve issues arising in the past or present. Rather, it is intended 
to provide a reasonable test of the safety of the repository by 
modeling through computer simulations a large number of ``alternative 
futures,'' incorporating the features, events, and processes required 
by the rule to be included in the assessment to determine if there is a 
reasonable expectation that the disposal system will meet regulatory 
standards. The assumptions identified by the commenter impose certain 
limitations on the scope of the performance assessments. These 
limitations are based on the application of scientific reasoning to 
data, testing, and analysis at hand on these issues and are for the 
purpose of enabling a reasonable test of repository safety.
    NRC has made a policy judgment that rulemaking is the better 
procedural vehicle to use to determine how the performance assessments 
should be constructed and, in particular, what limitations are 
appropriate to avoid unbounded speculation and to provide a reasonable 
test of repository safety. How this testing should be conducted is 
preeminently a matter of scientific and technical analysis. To the 
extent that there may be disagreement in the scientific community as to 
the scientific soundness of the assumptions and any limitations on 
assumptions to be incorporated into the performance assessments, the 
notice and comment rulemaking process is of particular value because it 
allows equal access to all viewpoints and best assures achievement of 
the ultimate goal of making sure that the testing of the safety of the 
repository rests on the best science available. The determination of 
what assumptions and limitations on assumptions are best suited to form 
a reasonable test is not aimed at determining the rights or liabilities 
of particular individuals and thus, the adjudicatory process is not 
conducive to selecting the ingredients of the tests used to provide a 
reasonable expectation of repository safety.
    Because neither EPA nor NRC have made ``determinations of 
adjudicative fact,'' as explained above, the question of the extent of 
EPA's authority under EnPA to establish standards through rulemaking 
that the commenter believes would otherwise be determinations of 
adjudicative fact does not arise. EPA has adequately addressed its 
jurisdiction to issue the standards that NRC is adopting in this final 
rule.
    The commenter may also be asserting that all the issues in this 
rulemaking are adjudicatory issues simply because the rule applies to 
only one entity, DOE, and the licensing of a repository at one site. A 
``rule,'' as defined in the Administrative Procedure Act, ``means the 
whole or part of an agency statement of general or particular 
applicability and future effect designed to implement, interpret, or 
prescribe law or policy'' 5 U.S.C. 551(4) (emphasis added). Thus, the 
fact that NRC's rule applies only to DOE and only to DOE's activities 
at one site does not, per se, turn the issues considered in this 
rulemaking into adjudicative issues determining adjudicative facts (See 
Attorney General's Manual on the Administrative Procedure Act, 1947, p. 
13 (``[R]ule'' includes agency statements not only of general 
applicability but also those of particular applicability applying 
either to a class or to a single person''); Anaconda Company v. 
Ruckelshaus, 482 F.2d 1301, 1306 (10th Cir. 1973)).
    The cases cited by the commenter, Heckler v. Campbell, 461 U.S. 458 
(1983), Broz v. Heckler, 711 F.2d 957 (11th Cir. 1983) (Broz II), and 
Opinion Modified on Denial of Rehearing by Broz

[[Page 10816]]

v. Heckler, 721 F.2d 1297 (11th Cir. 1983) (Broz III), in support of 
its view that NRC may not make ``determinations of adjudicatory fact'' 
in a rulemaking are similarly not relevant because no such 
determinations are being made in the final rule. These cases do not 
establish the broad principle stated by the commenter; i.e., that 
``[n]o agency may resolve a controversy over an adjudicative fact, 
relevant only to a single adjudication, by rulemaking.'' In Heckler v. 
Campbell, the Supreme Court upheld the Secretary of Health and Human 
Service's (HHS) reliance on rulemaking to establish guidance for the 
determination that jobs existed in the national economy within the 
capability of the disabled claimant against a claim that such a 
determination must be made in an individual adjudication. Broz 
considered the same guidance with respect to its application to the 
effect of age on disability determinations. Ultimately, in Broz III, 
the Eleventh Circuit of the U.S. Court of Appeals based its decision 
that this must be an individualized determination reached in an 
adjudication on its interpretation of Congress' intent in amending the 
Social Security Act (SSA) rather than on more sweeping statements about 
an agency's choice to use rulemaking or adjudication to achieve its 
mission.\2\ Finally, the Commission does not agree that resolving the 
issues the commenter has labeled ``determinations of adjudicative 
fact'' deprives the State of its right to a hearing under section 189a. 
of the AEA on these issues. As the Supreme Court has stated, ``the 
statutory requirement for a hearing * * * does not preclude the 
Commission from particularizing statutory standards through the 
rulemaking process and barring at the threshold those who neither 
measure up to them nor show reasons why in the public interest the rule 
should be waived'' (Federal Power Commission v. Texaco, Inc., 377 U.S. 
33, 39 (1964)).\3\
---------------------------------------------------------------------------

    \2\ The Eleventh Circuit initially construed the provisions of 
the SSA in terms of the distinction between adjudicative facts and 
legislative facts and concluded that the effect of age on disability 
was an adjudicative fact that could not be determined in a 
rulemaking. Broz v. Schweiker, 677 F.2d 1351 (11th Cir. 1982) (Broz 
I) Certiorari Granted, Judgment Vacated by Heckler v. Broz, 461 U.S. 
952 (1983). Upon remand for reconsideration in light of Campbell, 
the Eleventh Circuit, in Broz II, reaffirmed its original decision 
upon finding that the Supreme Court had left open the validity of 
the guidance with respect to its use in determining the effect of 
age on disability.
    \3\ The commenter believes that the rules which resolve these 
issues will be incapable of actually being applied as written 
because they will turn out to be based on outdated scientific 
evidence. If this should happen, any person can petition to amend 
the rules. In addition, NRC's procedural rules enable a party to an 
adjudicatory proceeding to petition that application of a rule be 
waived in circumstances when the rule would not serve the purposes 
for which it was adopted. See, 10 CFR 2.335(b).
---------------------------------------------------------------------------

    The commenter also believes that, as explained in its comments to 
EPA, EPA's ``findings of adjudicative fact,'' in its final rule, now 
being adopted in NRC's final rule, are without any technical basis and 
are contrary to sound science, and for that reason violate both EnPA 
and the AEA. The NRC's notice of proposed rulemaking notified potential 
commenters that comments such as these on EPA's revised standards 
should be directed to EPA for EPA's response.
    Issue 4: Should NRC have waited to propose its regulations until 
after EPA had finalized its standards?
    Comment. A number of commenters objected to the process NRC used to 
conduct this rulemaking, namely issuing a proposed rule adopting EPA's 
proposed standards before EPA issued its final standards. Commenters 
expressed the view that NRC conveyed the impression that EPA's proposed 
standards would be adopted in NRC's final rule, such that public 
comment on EPA's proposal would have no effect; that if NRC cared what 
potential commenters thought about EPA's proposal, it should have 
waited, considered the comments received by EPA, and developed NRC's 
rule based on EPA's final rule; that having the public comment period 
for both rules at the same time is confusing for concerned citizens and 
makes it difficult for them to comment on the NRC rule; and that NRC 
should provide an additional comment period on its rule if EPA's final 
rule departs substantially from its proposed rule.
    Response. NRC's process for conducting this rulemaking was intended 
to put in place revised regulations, consistent with EPA's final 
revised standards, because the court had vacated NRC's rule insofar as 
it incorporated EPA's 10,000 year compliance period. NRC also sought to 
inform potential commenters on both rules, of how NRC envisioned 
implementing the EPA's proposed standards. It was hoped that such 
information would be of value in developing comments on both proposals. 
NRC's intention has always been, consistent with its statutory 
obligations, to conform its final regulations to the final standards 
EPA would issue after EPA duly considers the comments it received.
    NRC emphasized in its notice of proposed rulemaking that comments 
on EPA's revised standards were to be addressed to EPA and that the 
scope of NRC's revised rule was limited to its adoption of EPA's 
revised standards, its proposal to allow DOE to use the same methods 
for calculating doses to workers during the operational period as those 
required for calculating public doses and its proposal to specify use 
of a deep percolation rate to represent the effect of future climate in 
performance assessments after 10,000 years. Thus, the narrow focus of 
NRC's rulemaking only required potential commenters to focus on two 
technical issues beyond the issues involved in EPA's proposal (i.e., 
setting a value for the deep percolation rate and use of modern 
dosimetry for estimating worker exposures). NRC extended the comment 
period by one month in response to public comments. For these reasons, 
we believe the public was given a fair opportunity to comment on NRC's 
proposal. NRC regrets any misimpression that NRC was assuming that 
EPA's proposed rule would become final as proposed without modification 
and that comments provided to EPA would have no effect. NRC made no 
such assumption and EPA has in fact made changes to its proposed rule 
in light of the comments it received.
    Finally, with respect to the request for an additional comment 
period if EPA's final rule is substantially different from its proposed 
rule, as stated above (see Background section of this document), EPA's 
final rule differs from its proposed rule in only two respects: the 
dose limit is set to 1.0 mSv/year (100 mrem/year) with the arithmetic 
mean as the statistical metric to be used to assess compliance; and its 
requirement that NRC either establish the magnitude of the water table 
rise and its significance as part of the seismic assessment, or require 
DOE to do this assessment. The first change responds favorably to the 
numerous public comments urging use of a dose limit lower than 3.5 mSv/
year (350 mrem/year) and use of the arithmetic mean as the measure of 
compliance. Similarly, in its final regulations, NRC requires DOE to 
include the magnitude of the water table rise and its significance in 
its seismic assessment submitted with the license application. As a 
result, this information would also be subject to litigation, absent 
any future NRC rulemaking on this subject. Because of these changes, 
the Commission believes there is no need for an additional comment 
period.

[[Page 10817]]

2. Clarification of NRC's Implementation of FEPs for the Performance 
Assessment for the Period After 10,000 Years

    Issue 1: Are the FEPs considered for the first 10,000 years after 
repository closure the only FEPs that need be considered for the entire 
post-closure period?
    Comment. The Nuclear Energy Institute (NEI) agreed with NRC's 
adoption of EPA's requirement that the same FEPs identified and 
screened for inclusion in performance assessments to show compliance 
with the standards for the initial 10,000 years after closure be used 
in performance assessments to show compliance with the post-10,000 year 
standards. However, NEI believes NRC should clarify that FEPs that are 
screened-in for the first 10,000 years after repository closure are the 
only FEPs that need be considered for the entire post-closure period. 
NEI provided the example that if DOE provides an adequate basis to 
screen-out post-closure criticality or microbially-influenced corrosion 
(MIC) effects during the first 10,000 years after repository closure, 
the Yucca Mountain Review Plan (YMRP) should specify that no additional 
consideration of criticality or MIC in the post-10,000 year period is 
necessary.
    Response. The requirements for FEPs to be included in the 
performance assessment for the period after 10,000 years are specified 
at Sec.  63.342. DOE is required to include those FEPs that are 
screened into the performance assessments for the first 10,000 years 
after repository closure and the four FEPs specifically identified for 
inclusion, i.e., seismicity, igneous activity, climate change, and 
general corrosion. Based on the requirements at Sec.  63.342, the 
specific FEPs (criticality or MIC) identified by the commenter would 
only be included in the performance assessment after 10,000 years if 
they were also included in the performance assessment for the first 
10,000 years (i.e., could not be screened out of the performance 
assessment for the first 10,000 years). The Commission does not believe 
further clarification to the regulation is necessary.
    Issue 2: Do the proposed changes to Sec.  63.114 ``Requirements for 
performance assessment'' impose additional limits on the performance 
assessment for the period after 10,000 years?
    Comment. The State of Nevada believes that Sec.  63.114(b) appears 
to include another limit beyond the limits in Sec.  63.342(c) on the 
post-10,000 year performance assessment and asks for clarification. NEI 
believes that NRC should more clearly assert that performance 
assessment methods meeting existing Part 63 requirements are also 
adequate for the post-10,000 year period.
    Response. The changes to Sec.  63.114 impose no additional limits 
on the performance assessment for the period after 10,000 years. The 
changes ensure consistency between NRC's regulations and EPA's final 
standards. In particular, EPA's final standards specify that FEPs used 
for the first 10,000 years should be used for estimating performance 
after 10,000 years. Thus, Sec.  63.114(b) specifies that the same 
performance assessment methods used for the first 10,000 years are to 
be used for the period after 10,000 years. For example, parameter 
ranges used in the performance assessment for the first 10,000 years 
would be used in the performance assessment for the period after 10,000 
years. Additional technical basis for selection of FEPs, beyond that 
developed for the performance assessment for the first 10,000 years, is 
not required. Thus, the changes at Sec.  63.114 ensure the performance 
assessment methods, such as the support and treatment of FEPs will be 
the same for the periods before and after 10,000 years, subject to the 
limits on performance assessments at Sec.  63.342. Some minor revisions 
have been made to Sec.  63.114(b) to further clarify the Commission's 
intent.
    Issue 3: Does the proposed treatment of a potential igneous event 
during the period after 10,000 years limit consideration of the effects 
of magma on spent fuel?
    Comment. The State of Nevada commented that the proposed regulation 
at Sec.  63.342(c)(1)(ii) specifies that the effects of an igneous 
event are limited to the effects of damage directly to the waste 
package. The State is concerned that NRC will not consider the effects 
of magma on the radioactive waste inside the waste package. The State 
asserts that effects on the contents of the waste package could be 
important for igneous events that occur at times after waste packages 
are already breached because of other processes (such as corrosion) and 
the radioactive waste may be more vulnerable to igneous events.
    Response. The regulations do not exclude consideration of the spent 
fuel in the treatment of a potential igneous event during the period 
after 10,000 years. The rule, at Sec.  63.342(c)(1)(ii), requires the 
igneous analysis to include damage to the waste package directly. Waste 
package is defined in Sec.  63.2 to mean ``the waste form and any 
containers, shielding, packing, and other absorbent materials 
immediately surrounding an individual waste container'' and waste form 
is defined in the same section to mean ``the radioactive waste 
materials and any encapsulating or stabilizing matrix.'' Thus, 
consideration of damage to the waste package would include 
consideration of damage to the radioactive waste materials inside the 
waste package.
    Issue 4: Should the seismic analysis exclude seismic activity from 
magma movement?
    Comment. NEI agreed with NRC's proposal to limit analysis of long-
term effects of seismicity to effects on the drifts in the repository 
and the waste package but requested that NRC clarify that seismic 
activity from magma movement need not be considered in the analysis. 
NEI suggests such a limitation is appropriate based on an Electric 
Power Research Institute (EPRI) analysis that demonstrates that seismic 
activity induced from magma movement is very minor, compared to seismic 
activity caused by tectonism.
    Response. Seismic activity includes activity from both tectonism 
and magma movement. Current methods to develop and quantify seismic 
ground motions, such as DOE's current Probabilistic Seismic Hazard 
Assessment, include consideration of seismic activity from volcanism or 
magma movement. Volcanic sources of seismic activity are often included 
as part of the background seismic source term. Therefore, the 
commenter's request for clarification, which would exclude seismic 
activity caused by magma movement from the seismic analysis, is not 
appropriate.
    Issue 5: Should NRC's rule set a requirement for assuring the 
statistical significance of DOE's modeling results in its performance 
assessments?
    Comment. The State of Nevada stated that NRC's rule should 
establish a requirement for DOE to prove mathematically that its 
modeling results are statistically significant (i.e., a sufficient 
number of ``runs'' or the set of probabilistic simulations used to 
simulate the wide range of possible future behaviors of the repository 
system have been performed).
    Response. The current regulations provide specific requirements at 
Sec.  63.114 for the performance assessment. Among these, for example, 
are proper consideration of uncertainty and variability in parameter 
values. The Commission believes it is neither necessary nor appropriate 
to further specify measures of statistical significance. Fundamental to 
any approach for representing uncertainty and variability is 
demonstrating how the results accurately represent the uncertainty and 
variability, for example,

[[Page 10818]]

by performing a sufficient number of probabilistic simulations. 
Determining what number of ``runs is sufficient'' is best left for DOE 
to present and defend, based on the approach used in the performance 
assessment and an understanding of the results. NRC is confident that 
its regulations for performance assessment require DOE to provide 
sufficient information for NRC to judge if DOE has performed enough 
probabilistic simulations.
    Issue 6: Will FEPs associated with atmospheric releases of 
radioactivity and exposure of residents downwind of Yucca Mountain be 
considered in the performance assessment for the period after 10,000 
years?
    Comment. Two commenters expressed concern over how FEPs associated 
with atmospheric releases of radioactivity and exposure of residents 
downwind of Yucca Mountain will be considered in the performance 
assessment for the period after 10,000 years, including FEPs associated 
with seismic and igneous FEPs.
    Response. The performance assessment for the period after 10,000 
years must include consideration of potential atmospheric releases of 
radioactivity. The NAS report, Technical Bases for Yucca Mountain 
Standards (1995), pp. 6-7, recommended that the exposure scenario be 
specified in the standards because of the difficulties in projecting 
where people may reside and how exposures might occur in the distant 
future (e.g., thousands to hundreds of thousands of years in the future 
and longer). Accordingly, EPA specified characteristics of the RMEI 
(66-FR 32134; June 13, 2001).
    Issue 7: Does the fact that the limitations on FEPs in the 
performance assessments are being established through rulemaking rather 
than adjudication, based on data available in 2005, mean that there 
will be no flexibility to take into account data and models used in 
DOE's license application or that DOE will have no incentive to further 
reduce uncertainties?
    Comment. The State of Nevada believes that the assumptions being 
used to account for uncertainty in the post-10,000 year period, and 
which are incorporated through this rulemaking into the limitations on 
the FEPs to be considered in DOE's performance assessments, are 
premature and render the rule inflexible because they are based on data 
available in 2005. NRC's rules must be sufficiently flexible to take 
into account data and models used in DOE's license application. The 
State fears that because the rules are premised on uncertainties as 
perceived through 2005 data and models, DOE will have a disincentive to 
reduce these uncertainties and add realism to its post-10,000 year 
performance assessment because it will wish to preserve the 
uncertainties and conservatisms that form the basis for the rules.
    Response. NRC's regulations afford DOE the flexibility to account 
for uncertainty in data and models. Such flexibility provides neither 
incentive nor disincentive to reduce uncertainties. The regulations, at 
Sec.  63.114, require DOE to account for the uncertainties in data and 
models in the performance assessment over the initial 10,000 years, and 
these same uncertainties are to be included in the performance 
assessment beyond 10,000 years. On June 3, 2008, DOE submitted a 
license application to NRC for authorization to construct a repository 
at Yucca Mountain. The NRC will review DOE's treatment of the 
uncertainties. DOE has the flexibility to decide where to reduce 
uncertainties; however, it must demonstrate there is a reasonable 
expectation that the performance objectives will be met. NRC 
regulations afford DOE appropriate flexibility for selecting and 
supporting its performance assessment, including the consideration of 
uncertainties, given the unique and difficult task of estimating 
performance of a geologic repository over thousands of years.
    The regulations do provide certain limitations, as specified in 
EPA's final standards, with respect to certain FEPs (i.e., seismicity, 
igneous activity, climate change, and general corrosion). Uncertainties 
in data and models for these FEPs are limited to those aspects of the 
FEPs considered most important to performance and the treatment of the 
uncertainties used in the performance assessment for the initial 10,000 
years (see also the response to Issue 2 under this topic). For example, 
the consideration of seismic events in the performance assessment for 
the period after 10,000 years would be based on the same seismic hazard 
curve, including its uncertainties, that was used in the performance 
assessment for the initial 10,000 years. However, the analysis for the 
period after 10,000 years would only consider the aspects of the 
seismic events that might be the most important to repository 
performance (i.e., damage to the drifts in the repository, failure of 
the waste package, and magnitude of the water table rise under Yucca 
Mountain).
    Finally, the commenter believes that the rules which resolve these 
issues will be incapable of actually being applied as written because 
they will turn out to be based on outdated scientific evidence. If this 
should happen, any person can petition to amend the rules. In addition, 
NRC's procedural rules enable a party to an adjudicatory proceeding to 
petition that application of a rule be waived in circumstances when the 
rule would not serve the purposes for which it was adopted (See, 10 CFR 
2.335(b)).

3. Climate Change

    Issue 1: Can the future climatic regime be bounded by the observed 
range of conditions over past glacial-interglacial cycles?
    Comment. One commenter indicated it is incorrect to presume that 
future climate conditions at Yucca Mountain can be bounded by the 
observed range of conditions over past glacial-interglacial cycles. To 
the extent this comment may refer to human-induced influences on 
climate, those influences are considered under a separate issue.
    Response. The Commission believes the future climatic regime can be 
bounded by the observed range of conditions over past glacial-
interglacial cycles. All climate predictions are based on and 
calibrated to evidence of past climates contained in the geologic 
record. The values specified for deep percolation rates adopted in the 
final regulation capture the range of temporal variability, 
uncertainty, and magnitude of deep percolation expected as a 
consequence of future climate change.
    The NAS committee (1995) was familiar with the science behind 
predicting future climate changes and stated, in its recommendations on 
Yucca Mountain standards, that a future ice age in the next few hundred 
years is ``unlikely but not impossible,'' in the next 10,000 years is 
``probable but not assured.'' However, over a 1-million-year time 
frame, the climate is much more likely to pass through several glacial-
interglacial cycles (i.e., ice ages). The NAS indicated there is a 
reasonable data base from which to infer past changes and noted that 
``(a)lthough the range of climatic conditions has been wide, 
paleoclimate research shows that the bounding conditions, the envelope 
encompassing the total climatic range have been fairly stable'' and 
that ``(b)ased on this record, it seems plausible that the climate will 
fluctuate between glacial and interglacial stages during the period 
suggested for the performance assessment calculations.'' Further, in 
its 1995 findings, the NAS stated that ``enough of the important 
aspects [of climate change] can be known within reasonable limits of 
uncertainty, and these properties and processes are sufficiently 
understood and stable over the long time scales of interest to make 
calculations possible

[[Page 10819]]

and meaningful, we believe that there is a substantial scientific basis 
for making such calculations, taking uncertainty and natural 
variability into account.''
    Issue 2: Should human-induced influences on climate be considered 
when bounding the future climatic regime?
    Comment. One commenter noted that human-induced (i.e., 
anthropogenic) influences on climate from fossil fuel combustion and 
the resulting persistence of greenhouse gases in the atmosphere are the 
main issues to consider in predicting future climatic conditions. These 
anthropogenic effects might cause substantial reorganization of 
atmospheric systems, both before and after 10,000 years, that increase 
the number and intensity of extreme storm events at Yucca Mountain. The 
commenter believed that the highly non-linear hydrologic response of an 
arid system like Yucca Mountain to such extreme events would affect the 
performance of the repository and invalidate the use of the long-term 
average climate proposed in the Part 63 revisions. The same commenter 
also noted that the predictive challenges of simulating these 
postulated extreme events could be met through use of existing and 
soon-to-be-available global circulation models (GCMs) that explicitly 
incorporate atmospheric composition and evolution in predicting future 
climate conditions. In presuming use of these models, this commenter 
noted that uncertainties in climate prediction do not change in the 
period beyond 10,000 years, at least in terms of the range of climate 
conditions that could occur, but rather that their detailed timing may 
change. Another commenter speculated that the same anthropogenic 
climate effects might delay the onset and reduce the magnitude of full 
glacial cycles, resulting in longer interglacial periods that would be 
warmer and drier than present-day conditions. Accordingly, this second 
commenter felt that the use of long-term average climate conditions 
represented by the values specified for deep percolation rates in the 
proposed Part 63 revisions was overly conservative and that less water 
would reach the repository horizon.
    Response. NRC considered the effects of anthropogenic influences on 
climate change. Based on that evaluation, the NRC believes the range of 
values specified for deep percolation rates adopted in the final rule 
captures the range of temporal variability, uncertainty, and magnitude 
of deep percolation expected as a consequence of future climate change.
    The magnitude and timing of the anthropogenic effects suggested by 
the commenter are likely to be more pronounced during the first 10,000 
years. The final regulation addresses only the 10,000 to 1 million year 
time period, during which any anthropogenic effects are anticipated to 
diminish. Anthropogenic effects, as represented in the GCMs cited by 
the commenter, might persist for 100,000 year time periods, but they do 
not fluctuate periodically and they decrease with time after an initial 
peak. Therefore, NRC believes that these effects can be captured by the 
long-term average infiltration values adopted in the final regulation 
because the range of values for the sampled population bounds these 
effects in an appropriately conservative manner.
    Atmospheric reorganization and increased frequency and magnitude of 
extreme events might result from natural or anthropogenic climate 
change. However, extreme 10-to 20-year events effectively become long-
term averages that are incorporated into the range specified for deep 
percolation in the final regulation, when simulating a time period of 1 
million years.
    The Paintbrush non-welded tuff unit (PTn unit) overlying the 
potential repository dampens the effects of transient phenomena 
associated with shorter time frames (Manepally, C., et al., ``The 
Nature of Flow in the Faulted and Fractured Paintbrush Nonwelded 
Hydrogeologic Unit,'' San Antonio, TX: Center for Nuclear Waste 
Regulatory Analyses, April 2007) in the system's response to external 
hydrologic events. The NAS also recognized that long-term net 
infiltration averages can bound and describe Yucca Mountain hydrology 
adequately, stating that ``the subsurface location of the repository 
would provide a temporal filter for climate change effects on 
hydrologic processes'' The commenter also acknowledged this, quoting 
Cohen, ``no evidence shows that high-frequency fluctuations (a few 
years or shorter) penetrate to the depth of the potential repository'' 
(Cohen, S., ``Assumptions, Conservatisms, and Uncertainties in Yucca 
Mountain Performance Assessments,'' S. Cohen & Associates, prepared for 
U.S. Environmental Protection Agency, August 8, 2005). Flow simulations 
have shown that the non-welded PTn rock unit effectively damps out 
decadal flow transients. Also, as the first commenter notes, `frequent 
events' are mitigated by evapotranspiration. If high-precipitation 
events occur more frequently, the concomitant increases in soil 
formation and vegetation likely will mitigate the potential for 
increased infiltration, because net infiltration correlates inversely 
with soil thickness and extent of vegetative cover. Given the expected 
ratios of infiltration to precipitation, infiltration estimates of 15 
to 60 mm (0.6 to 2.4 in.) per event would result if all precipitation 
were to infiltrate. In reality, a substantial fraction of such high 
precipitation will run off or evapotranspire. Accordingly, long-term 
deep percolation as specified in the proposed rule captures these 
events in an appropriately conservative manner.
    The points raised by the second commenter illustrate the divergence 
of scientific opinions about the nature and magnitude of natural and 
anthropogenically influenced climate change, particularly at the sub-
regional scale necessary for net infiltration predictions at Yucca 
Mountain. The natural and anthropogenic effects associated with climate 
change are uncertain at this scale. Predictions will vary in timing, 
frequency, and magnitude of climatic variables such as temperature and 
precipitation, and therefore, net infiltration and deep percolation. 
The first commenter notes that climate change might result in wetter 
conditions resulting in insufficiently conservative predictions; the 
second commenter is concerned that conditions at Yucca Mountain might 
be drier in the future, resulting in overly conservative predictions. 
The first commenter refers to Cohen (2005) with respect to certain 
aspects of this issue; however, Cohen (2005) also notes that 
``(a)nthropogenic climate changes could reduce possibility of future 
glacial climates, lowering long-term infiltration rates and reducing 
dose.''
    In conclusion, the range of uncertainty and variability in 
predictions of future climate, including that associated with 
anthropogenic changes, and the resulting deep percolation are captured 
by the range of values specified in the final regulation.
    Issue 3: Is the nature and extent of the future climatic regime 
reasonably represented by the stylized scenario where constant climate 
conditions take effect after 10,000 years and continue through the time 
of geologic stability?
    Comment. Some commenters were concerned about the proposed future 
climate scenario, in which the future climate is represented by 
constant-in-time conditions that take effect after 10,000 years and 
continue through the time of geologic stability. The commenter's 
general concern is that assuming constant conditions may underestimate 
the hydrologic response at Yucca Mountain by failing to consider 
explicitly either variable dry and wet periods or changes in soils,

[[Page 10820]]

vegetation, and the watershed geomorphic characteristics in performance 
assessments over the time of geologic stability. Specifically, one 
commenter states that using constant-in-time infiltration rates is non-
conservative because a performance assessment conducted with this 
assumption would underestimate doses to the RMEI. The stated basis for 
this conclusion is that transient changes from dry to wet conditions in 
the repository cause greater radionuclide releases because localized 
corrosion of the waste packages is more likely under drier conditions. 
Also the exposed waste form is more likely to be dissolved and 
radionuclides are more apt to be transported to the biosphere under 
subsequent wet conditions.
    Response. The range and distribution of deep percolation rates 
adopted in the final regulations appropriately reflect the uncertainty 
in the area-averaged water flux through the footprint of the potential 
repository during the period after 10,000 years and are a reasonable 
basis for estimating and evaluating the long-term safety of the 
repository.
    The range and distribution of deep percolation rates adopted in the 
final regulation are not, in fact, based on constant climate 
conditions. The technical bases for the deep percolation range subsume 
time-variant climate conditions, whose future periodicity and magnitude 
are based on and calibrated to the range of conditions preserved in the 
geologic record, which includes geomorphic changes. In addition, the 
hydrogeologic properties of the PTn unit overlying the repository 
horizon, where present, dampen the magnitude of short term fluctuations 
in deep percolation that might be associated with future climate change 
or variability in precipitation (Manepally, C., et al., ``The Nature of 
Flow in the Faulted and Fractured Paintbrush Nonwelded Hydrogeologic 
Unit,'' San Antonio, TX: Center for Nuclear Waste Regulatory Analyses, 
April 2007). NAS acknowledges the phenomenon by indicating that ``(t)he 
subsurface location of the repository would provide a temporal filter 
for climate change affects on hydrologic responses. For this reason, 
climate changes lasting on the order of hundreds of years would have 
little, if any, effect on repository performance.''
    The commenter's argument that doses to the RMEI would be 
underestimated appears to be based on results from preliminary 
performance assessments conducted by DOE in which localized corrosion 
is the predominant mode of waste package failure. Preliminary waste 
package models developed by DOE indicate that the Alloy 22 outer 
container is susceptible to localized corrosion predominantly during 
the first few thousands of years, when waste package temperatures are 
high and concentrated solutions could develop. At times beyond 10,000 
years, when waste package temperatures are lower, the relative humidity 
within the emplacement drift is high, and solutions are less 
concentrated; the waste package is less susceptible to localized 
corrosion. Because general corrosion appears to be the dominant mode of 
waste package failure after 10,000 years, precise modeling of transient 
changes from drier to wetter conditions is unlikely to have a 
pronounced effect on peak expected dose.
    The commenter's argument does not appear to consider 10 CFR 63.303, 
which states that ``compliance is based upon the mean of the 
distribution of projected doses of DOE's performance assessments.'' The 
1995 NAS document at page 77 concluded that ``[a]lthough the typical 
nature of past climate change is well known, it is obviously impossible 
to predict in detail either the nature or the timing of future climate 
change.'' Although the science of climatology has advanced 
significantly in the 15 years after the publication of the NAS report, 
predicting the timing of dry-to-wet transitions remains highly 
uncertain. Even if it were true that ``[p]eak dose is likely to occur 
when a wet period follows a long period of unusually dry conditions'' 
as indicated by the commenter, dry-to-wet transients in performance 
assessments would have less influence on the mean of the distribution 
of projected doses than on any single projected dose used to construct 
the distribution. Specifically, simulations done by the NRC using its 
performance assessment code (TPA Version 4.1j) exhibited similar 
repository performance, in terms of dose, under constant and non-
constant climate scenarios (``Regulatory Perspective on Implementation 
of a Dose Standard for a One-Million Year Compliance Period,'' T. 
McCartin, Proceedings of the 2006 Materials Research Society Fall 
Meeting, Volume 985 from the Materials Research Society Proceedings 
Series). In these simulations, the non-constant climate scenarios were 
developed using cyclic variations caused by orbital parameters. Also, 
the constant climate scenarios used deep percolation values specified 
in NRC's proposed regulations. Performance assessment models and 
analyses continue to improve; however, dry-to-wet conditions appear to 
have a limited effect on the mean dose within the constraints of 
current performance assessment approaches.
    Issue 4: What is the range of future mean annual precipitation 
rates used to estimate future mean annual deep percolation rates?
    Comment. The State of Nevada commented that the upper bound of the 
future precipitation rate stated in the discussion section preceding 
the proposed regulation is lower than that used by DOE. DOE commented 
that the precipitation rates discussed in the proposed regulation do 
not represent the full range of expected climates. The Advisory 
Committee on Nuclear Waste suggested including additional documentation 
in the final rule for the approach used to calculate average 
precipitation rates over the post-10,000 year period.
    Response. NRC has conducted detailed climate analyses that 
considered time-varying values of historic, inferred prehistoric, and 
potential future precipitation rates to support the range of long-term-
average future deep percolation rates adopted in the final regulations. 
These time-varying precipitation rates were also used to estimate the 
range and bounds of 1-million-year-average annual precipitation. Having 
considered the comments and conducted further analyses, the Commission 
believes the time-varying precipitation rates used to estimate future 
mean annual deep percolation rates are appropriate.
    The lowest and highest values of the 1-million-year-average future 
annual precipitation in any climate sequence used to estimate the 1-
million-year-average future deep percolation rate are 211 and 471 mm/
year (8.3 and 18.5 in./year) at a 1,524 meter (5,000 foot) reference 
elevation. NRC used two approaches, which are described by Stothoff and 
Walter, ``Long-Term Average Infiltration at Yucca Mountain, Nevada: 
Million-Year Estimates,'' San Antonio, TX: Center for Nuclear Waste 
Regulatory Analyses (2007), to estimate time-varying sequences of mean 
annual precipitation that vary over glacial cycles. Both approaches 
estimate precipitation for glacial stages, with the sequence of glacial 
stages determined using well-known orbital dynamics relationships. The 
first approach is based on the climate reconstruction by Sharpe, 
``Future Climate Analysis: 10,000 Years to 1,000,000 Years After 
Present,'' Reno, NV: Desert Research Institute (2003), with present-day 
and monsoon climatic conditions adjusted to reflect historical 
precipitation measurements in the vicinity of Yucca Mountain based on 
meteorological data in Bechtel SAIC Company (BSC),

[[Page 10821]]

``Simulation of Net Infiltration for Present-Day and Potential Future 
Climates,'' Las Vegas, NV: Bechtel SAIC Company, LLC (2004). The 1-
million-year-average mean annual precipitation rate from the first 
approach ranges from 213 to 389 mm/year (8.4 to 15.3 in./year), and 
with a mean of 315 mm/year (12.4 in./year) and a standard deviation of 
52 mm/year (2.0 in./year). The second approach is based on estimated 
sequences of future continental ice volumes, which respond to 
insolation variation caused by orbital dynamics, with changes in 
precipitation related to changes in atmospheric patterns occurring from 
changes in continental ice volume. The 1-million-year-average mean 
annual precipitation for the second approach ranges from 211 to 471 mm/
year (8.3 to 18.5 in./year), and with a mean of 322 mm/year (12.7 in./
year) and a standard deviation of 47 mm/year (1.8 in./year).
    Both approaches described by Stothoff and Walter, ``Long-Term 
Average Infiltration at Yucca Mountain, Nevada: Million-Year 
Estimates,'' San Antonio, TX: Center for Nuclear Waste Regulatory 
Analyses (2007) subdivide the 1-million-year period into a sequence of 
interglacial and glacial stages that vary in duration from 500 to 
40,000 years. For each stage, a range of mean annual precipitation is 
estimated that includes uncertainty. The smallest and largest values of 
estimated mean annual precipitation considered in any stage are 162 and 
581 mm/year (6.4 and 22.9 in./year).
    Issue 5: What is the range of future deep percolation rates?
    Comment. A number of commenters endorsed the approach of specifying 
the rate of water flow through the Yucca Mountain repository (expressed 
as deep percolation rate) as an appropriate and practical approach to 
adopting EPA's requirement to consider the effect of climate variation 
after 10,000 years. Several commenters indicated that the basis for the 
proposed regulation was not clearly explained. Also, several commenters 
questioned the specific range of deep percolation rates discussed in 
the proposed regulation. The State of Nevada raised a number of 
additional concerns. First, the State questioned the validity of 
estimating infiltration using a constant climate state. Second, the 
State questioned the range of uncertainty used to represent 
infiltration for present-day and future climate in the long-term-
average estimates. Third, the State questioned the adequacy of computer 
models (e.g., one-dimensional models without lateral distribution) to 
extrapolate net infiltration values to future climates. Fourth, the 
State questioned the assumption that plant and soil regimes remain 
stationary during future climate states. Another commenter was 
concerned with the assumption that spatial variability of infiltration 
remains constant over time. NEI commented that requiring climate to be 
assumed constant at present-day conditions over the post-10,000 year 
period would be a more appropriate implementation of a stylized 
approach. NEI also considered the range of 5 to 20 percent for the 
ratio of the deep percolation rate to precipitation rate, used to 
support the deep percolation rates in the proposed rule, was too large 
and provided an alternative range of 5 to 10 percent. DOE commented 
that deep percolation rates appear to be skewed to the maximum deep 
percolation rate rather than a rate obtained from the full range of 
expected climate.
    Response. Having considered the comments and conducted further 
analyses, the final regulations specify a slightly different range for 
the deep percolation rate from the proposed rule. The final rule now 
specifies that deep percolation rates averaged over the period of 
10,000 to 1 million years in the future may be reasonably described 
with a``truncated'' lognormal distribution,\4\ which varies between 10 
and 100 mm/year (0.39 and 3.9 in./year). To address commenters' 
concerns with respect to certain simplifying assumptions used to 
estimate the deep percolation rates (e.g., range of 5 to 20 percent for 
the ratio of the deep percolation rate to precipitation rate) the NRC 
has conducted more sophisticated analyses, which are now used to 
support the estimates for the deep percolation rates. The distribution 
of deep percolation rates is based on the analysis of Stothoff and 
Walter, ``Long-Term Average Infiltration at Yucca Mountain, Nevada: 
Million-Year Estimates,'' San Antonio, TX: Center for Nuclear Waste 
Regulatory Analyses (2007), who estimated deep percolation areally 
averaged within a rectangle overlying the repository footprint 
considering uncertainty in both climate and net infiltration. The 
analysis suggested that long-term-average deep percolation is better 
represented by a ``truncated'' lognormal distribution than the 
originally proposed log-uniform distribution that ranged from 13 to 64 
mm/year (0.5 to 2.5 in./year). The NRC adopted a ``truncated'' 
lognormal distribution between the 5th and 95th percentiles of the 
lognormal distribution to represent reasonable lower and upper limits 
for the long-term average deep percolation rates. The revised 
distribution for deep percolation is consistent with available deep 
percolation estimates from Yucca Mountain, recharge estimates from a 
wide range of elevations in central and southern Nevada, and 
uncertainty estimates from a numerical model. The ``truncated'' 
lognormal distribution has an arithmetic mean of 37 mm/year (1.5 in./
year) for the deep percolation rate as compared to an arithmetic mean 
of 32 mm/year (1.3 in./year) based on the range and distribution in the 
proposed regulations. Although the upper limit of the deep percolation 
rate [i.e., 100 mm/year (3.9 in./year)] in final regulations is almost 
twice the upper limit in the proposed regulation [i.e., 64 mm/year (2.5 
in./year)], the deep percolation rates in the final regulations, on 
average, represent only slightly wetter conditions than what was 
specified in the proposed regulations [i.e., arithmetic mean of 37 
versus 32 mm/year (1.5 versus 1.3 in./year)]. Truncation of the 
lognormal distribution between 10 and 100 mm/year (0.39 and 3.9 in./
year) results in reasonable lower and upper limits for the long-term 
average deep percolation rates. If the lower and upper limits were 
extended further, the resulting arithmetic mean of the distribution 
would change very little because of the decreasing probability of 
values that occur at the tails (or extremes) of a lognormal 
distribution.
---------------------------------------------------------------------------

    \4\ The truncated lognormal distribution is based on a lognormal 
distribution with an arithmetic mean of 41 mm/year (1.6 in./year) 
and a standard deviation of 33 mm/year (1.3 in./year). The 5th and 
95th percentiles of this lognormal distribution are approximately 10 
and 100 mm/year (0.39 and 3.9 in./year), respectively.
---------------------------------------------------------------------------

    To document more clearly the technical bases for the proposed range 
of long-term-average future deep percolation rates expected at Yucca 
Mountain during the post-10,000 year period, the NRC conducted 
additional detailed climate and infiltration analyses, which are 
reported in Stothoff and Musgrove, ``Literature Review and Analysis: 
Climate and Infiltration,'' San Antonio, TX: Center for Nuclear Waste 
Regulatory Analyses (2006) and Stothoff and Walter (2007). Stothoff and 
Musgrove (2006) provide a comprehensive review and analysis of relevant 
infiltration and recharge studies that have been conducted for the 
Yucca Mountain region, the Death Valley region, the southern and 
central Great Basin of Nevada, and analogous arid to semi-arid regions 
in the western United States and the world. Stothoff and Walter (2007) 
describe additional technical investigations of estimated precipitation 
rates and temperatures for the past 1 million years in the Yucca

[[Page 10822]]

Mountain region based on various climate proxy data reported in the 
literature. Stothoff and Walter (2007) link these past precipitation 
and temperature estimates with a well-accepted glacial model based on 
orbital dynamics to estimate precipitation and temperature sequences 
for the next 1 million years. Finally, Stothoff and Walter (2007) use 
these future climate sequences with infiltration relationships 
supported by the data described in Stothoff and Musgrove (2006) and 
site observations at Yucca Mountain to estimate the range of long-term-
average future deep percolation rates at Yucca Mountain during the 
post-10,000 year period.
    Contrary to inferences made by the State of Nevada, the revised 
distribution for deep percolation does not use steady-state hydrology 
based on annual average precipitation to estimate deep percolation. 
Stothoff and Walter (2007) considered the time-varying response of net 
infiltration to precipitation at time scales ranging from individual 
precipitation events, to decadal-scale averages, to millennial-scale 
glacial stages to derive estimates of long-term-average deep 
percolation.
    Stothoff and Walter (2007) considered the response of net 
infiltration to climate at approximately 16,000 locations across Yucca 
Mountain to derive estimates of long-term-average deep percolation 
averaged over the repository footprint. Uncertainty in each of the 
hydraulic and climatic factors affecting infiltration was considered at 
each of the 16,000 locations. Stothoff and Walter (2007) found that a 
lognormal distribution for areal-average net infiltration reasonably 
reflects the effect of the uncertainty in these factors. Stothoff and 
Walter (2007) did not use the INFIL version 2 model developed by the 
U.S. Geological Survey (USGS) for this analysis, nor did they neglect 
lateral redistribution of runoff.
    The State of Nevada questioned the appropriateness of using a 
stationary hydrologic state to describe plant and soil characteristics 
in numerical modeling and another commenter was concerned with the 
assumptions that the spatial variability of infiltration remains 
constant over time. The deep percolation model described by Stothoff 
and Walter (2007) does not use a stationary description for plant 
uptake. It does use a stationary description for soil characteristics 
but recognizes that soil thicknesses and soil texture may change over a 
glacial cycle. Stothoff and Walter (2007) consider the likely influence 
of such changes on net infiltration to be relatively small compared to 
the overall uncertainty in net infiltration. Soil evolution under 
glacial conditions will tend to deepen soil profiles over time and make 
the soil texture finer than at the present time, which would tend to 
reduce net infiltration at the end of a long, wetter glacial interval. 
Soil cover tends to erode under interglacial conditions, which may 
promote net infiltration during dry intervals. NRC considers it 
reasonable to neglect soil evolution because soil evolution would tend 
to make net infiltration under both glacial and interglacial climatic 
states more like the long-term-average infiltration. Although soil 
properties are stationary in the deep percolation model in Stothoff and 
Walter (2007), plant uptake is not and therefore the spatial 
variability of deep percolation in the model of Stothoff and Walter 
(2007) is not constant over time.
    NEI commented that the 1-million-year-average deep percolation 
rates used for performance assessments should be maintained at present-
day values because this would be more conservative with respect to 
groundwater usage for dose calculations for the RMEI. Deep percolation 
rates in Yucca Mountain do not affect the groundwater usage rate of the 
RMEI for evaluating compliance with the post-10,000 year individual 
protection standard. Groundwater usage rates at the location of the 
RMEI as prescribed at 10 CFR 63.312(c) are fixed at an annual water 
demand of 3.7 million cubic meters (3,000 acre-feet). DOE commented 
that, considering the analyses by Sharpe ``(Future Climate Analysis: 
10,000 Years to 1,000,000 Years After Present,'' Reno, NV: Desert 
Research Institute, 2003), the proposed probability distribution was 
skewed towards maximal percolation rates because the full range of 
potential climates was not considered in the regulation. Stothoff and 
Walter (2007) compared net infiltration estimates using potential 
future climate sequences obtained from an independent model based on 
site and regional observations and a global ice volume model, and 
sequences obtained from a slightly modified version of the Sharpe 
(2003) model. The Sharpe (2003) model was modified to update the 
present-day climate with site-specific present-day climate observations 
from BSC (``Simulation of Net Infiltration for Present-Day and 
Potential Future Climates,'' Las Vegas, NV: Bechtel SAIC Company, LLC, 
2004). The modified Sharpe model yields an estimate for long-term-
average deep percolation with a mean value of 44 mm/year (1.7 in./year) 
and values of 9.9 and 103 mm/year (0.39 and 4.1 in./year) at the 5th 
and 95th percentiles, respectively. The independent model, which was 
used to specify the deep percolation distribution in the regulation, 
has a mean value of 41 mm/year (1.6 in./year) and values of 10 and 102 
mm/year (0.39 and 4.0 in./year) at the 5th and 95th percentiles, 
respectively. Because the two independent climate sequences consider a 
wide range of potential climates yet yield similar infiltration 
estimates, the NRC believes the distribution of deep percolation rates 
adopted in the final regulation is not skewed toward maximal 
percolation rates.
    Issue 6: Is the NRC guidance document on uncertainty and analysis 
of infiltration and subsurface flow and transport, intended for Site 
Decommissioning Management Plan (SDMP) sites, applicable to 
establishing an appropriate stylized climate scenario for times beyond 
10,000 years at the potential high-level radioactive waste (HLW) 
disposal site at Yucca Mountain?
    Comment. One commenter noted there is no clear indication whether 
or how NRC's existing guidance on accounting for uncertainty when 
establishing infiltration rates has been applied. Specifically, the 
commenter referred to NUREG/CR-6565, ``Uncertainty Analysis of 
Infiltration and Subsurface Flow and Transport for SDMP Sites'' (1997).
    Response. The guidance presented in NUREG/CR-6565 is intended to be 
used only at SDMP sites. Therefore, NUREG/CR-6565 is not directly 
applicable to a potential high-level waste disposal site. However, the 
methods NRC uses to account for uncertainty in its independent estimate 
of infiltration rates (deep percolation) for both present and future 
climatic conditions at Yucca Mountain encompass and exceed in 
sophistication the methods discussed in NUREG/CR-6565. The technical 
methods used by the NRC to account for uncertainty are discussed in 
detail under Issue 5 (What is the range of estimated present-day deep 
percolation rates and the appropriate range of future deep percolation 
rates?).
    The guidance in NUREG/CR-6565 applies to SDMP sites and recommends 
an appropriate level of modeling sophistication commensurate with the 
risk of such sites. This is consistent with NRC's general approach of 
using simple models for simple sites with low likelihood of exceeding 
exposure criteria, and using increasingly sophisticated models and 
requiring more robust data for more complex sites that pose potentially 
greater risks to public safety. The more detailed

[[Page 10823]]

requirements in Part 63 and the associated guidance in the YMRP are 
appropriate for the site complexity of Yucca Mountain and for the 
greater risk associated with HLW disposal.
    For example, NUREG/CR-6565 recommends the use of generic models, 
such as Residual Radiation (RESRAD) and Multimedia Environmental 
Pollutant Assessment System (MEPAS), which simplify the physical system 
to reduce computational effort. Conversely, a site-specific performance 
assessment model with all the processes considered important at Yucca 
Mountain is needed to determine if Part 63 performance objectives are 
met. Both generic models and site-specific models are typically run in 
Monte Carlo mode to address uncertainty. In addition, NUREG/CR-6565 
provides tables of generic hydraulic parameter distributions to use in 
lieu of site-specific parameters that are not typically available for 
SDMP sites, whereas the YMRP provides technical acceptance criteria for 
data sufficiency and uncertainty specific to Yucca Mountain.
    Issue 7: To what degree does the stylized climate scenario depend 
on information provided by the USGS?
    Comment. One commenter indicated NRC's proposal is unsupportable 
because it is based on the past work of USGS personnel that is the 
subject of continuing criminal and civil investigation because of the 
apparent falsification of infiltration data and associated quality 
assurance records.
    Response. The stylized climate scenario and deep percolation rate 
in the final rule do not depend only on information provided by the 
USGS. The NRC has developed its own model and has performed independent 
field observations and measurements to support this final rule. In 
addition, the NRC has evaluated other regional information to 
corroborate its estimates of percolation under different climate 
regimes (Stothoff and Musgrove, ``Literature Review and Analysis: 
Climate and Infiltration,'' San Antonio, TX: Center for Nuclear Waste 
Regulatory Analyses, 2006).
    To address uncertainty in estimates of net infiltration (and hence, 
deep percolation) during future climates, NRC developed its own 
independent climate and net infiltration models. Some DOE information 
that NRC judged to be reasonable from a scientific perspective was used 
in the model inputs. Further, NRC understands that DOE has reaffirmed 
the quality of data used in response to the USGS e-mail issue 
investigations. For important model inputs, NRC independently collected 
data to gain confidence in the model results.
    Three of the most important model inputs are precipitation, soil 
thickness, and incident solar energy. For precipitation, NRC analyzed 
local and regional data patterns and developed a future climate model 
based on ice core volumes (Stothoff and Walter, ``Long-Term Average 
Infiltration at Yucca Mountain, Nevada: Million-Year Estimates,'' San 
Antonio, TX: Center for Nuclear Waste Regulatory Analyses, 2007). NRC 
climate model results were compared with indirect observations such as 
lake records and glacier advances in the Sierra Mountains. For soil 
thickness, NRC made its own measurements at the ridges and hillslopes 
of Yucca Mountain (Fedors, ``Soil Depths Measured at Yucca Mountain 
During Site Visits in 1998,'' Interoffice Note to J. Guttmann, 
Washington, DC: Nuclear Regulatory Commission, January 9, 2007). NRC 
used the measurements of soil depth to gain confidence in its own model 
for soil thickness across the Yucca Mountain area. For the incident 
solar energy, which is important for evaporation in this semi-arid 
climate, NRC independently developed its own energy model from the 
general literature (Stothoff, ``BREATH Version 1.1--Coupled Flow and 
Energy Transport in Porous Media: Simulator Description and User 
Guide,'' Washington, DC: Nuclear Regulatory Commission, 1995).
    Previously, NRC had developed a bulk bedrock permeability model 
(Waiting, et al. ``Technical Assessment of Structural Deformation and 
Seismicity at Yucca Mountain, Nevada,'' San Antonio, TX: Center for 
Nuclear Waste Regulatory Analyses, 2001) and performed independent soil 
permeability measurements, which provided a basis to evaluate the 
reasonableness of related DOE data ``Infiltration Tabulator for Yucca 
Mountain: Bases and Confimation,'' San Antonio, TX: Center for Nuclear 
Waste Regulatory Analyses, August, 2008; and Fedors (Soil Hydraulic 
Properties Measured During Site Visits to Yucca Mountain, Nevada,'' 
Interoffice Note to E. Peters, Washington, DC: Nuclear Regulatory 
Commission, August, 2008).
    NRC's model for estimating net infiltration is independent of the 
DOE model and uses a different conceptualization. The NRC model is a 
physically-based numerical heat and mass transfer model, which solves 
the Richards equation for water flow, with hourly climatic inputs to 
determine net infiltration for a range of climates and hydraulic 
property sets. Results from the heat and mass transfer model are used 
to develop an abstraction that is applied to Geographical Information 
System (GIS) based inputs covering the Yucca Mountain area. In 
addition, a surface water flow model based on the kinematic wave 
equation and linked to a two-layer infiltration algorithm is used to 
develop abstracted results to account for the effect of runoff and 
runon. The DOE model, on the other hand, is based on a water balance or 
``bucket,'' approach. The DOE model is applied within a GIS framework 
and includes surface water routing.
    Irrespective of the USGS matter, NRC is confident its model for 
estimating net infiltration is reasonable, because NRC has developed 
its model independent of DOE and DOE's contractors, NRC performed 
independent field observations and measurements, and NRC evaluated 
other regional information to corroborate its estimates of deep 
percolation rates under different climate regimes.
    Issue 8: Does NRC's specification of a particular value for deep 
percolation at this time limit the consideration of future scientific 
information for changing the specified value?
    Comment. One commenter stated that the specification of an 
infiltration rate years before DOE's license application is even filed 
is premature and unwise given the potential for new models for 
infiltration, which will likely have enhanced spatial and temporal 
resolution. Another commenter stated that if DOE's climatic analysis 
and forecast differ from the deep percolation rates set in the amended 
rule, then NRC's specification for deep percolation should serve as a 
point of reference in NRC's license review proceedings. NRC license 
reviewers should be open to the possibility that other analytical 
methods may exist for addressing future climate changes for such long 
periods. New models for climate change may include consideration of 
potential future anthropogenic influences on Yucca Mountain.
    Response. The Commission disagrees with the commenters. The NRC 
recognizes that scientific progress is expected to continue the 
understanding of potential future climate. However, the intention of 
the rule is to specify a reasonable basis for evaluating safety using 
current knowledge. Given the current approach for estimating deep 
percolation, it would take a major shift in scientific understanding 
for the deep percolation rates to change significantly. For example, if 
future scientific advances suggest there is a period when there would 
be no rainfall in the Yucca Mountain area for a period of 100,000 
years, this would result in a ten percent

[[Page 10824]]

change in the long-term average over the 1-million-year period. Such 
changes are not expected to significantly change dose estimates. 
However, if future scientific advances show the regulation is no longer 
sufficiently protective of public health and safety and the 
environment, NRC would not hesitate to propose appropriate changes to 
the regulations.
    Further, if any person believes that the specification for climate 
change no longer provides a reasonable basis for demonstrating 
compliance based on new scientific evidence, they can petition NRC to 
amend the rules. In addition, NRC's procedural rules enable any party 
to an adjudicatory proceeding to petition that application of a rule be 
waived in circumstances when the rule would not serve the purposes for 
which it was adopted [See also response to Issue 3 under NRC Adoption 
of EPA Standards and Response to Issue 7 under Clarification of NRC's 
Implementation of FEPs for the Performance Assessment for the Period 
after 10,000 Years of this document].
    Issue 9: Does NRC's analytical basis for its specification of a 
deep percolation rate comply with the Information Quality Act (IQA) and 
the associated Office of Management and Budget (OMB) guidelines?
    Comment. The State of Nevada stated that NRC's calculations and 
judgments did not undergo scientific peer review, contrary to the IQA 
and OMB guidelines. The State asserted that NRC is overwhelmingly 
relying on EPA information and indirectly on EPA's contractor documents 
cited in the proposed standards.
    Response. NRC considers its calculations and technical bases 
supporting the deep percolation estimates to be consistent with the IQA 
and the associated OMB guidelines concerning peer review. The OMB peer 
review guidance applies to ``influential scientific information'' that 
will have a clear and substantial impact on important public policies 
or the private sector (70 FR 2667; January 14, 2005). The distribution 
and range for deep percolation rates have a limited effect on 
repository performance and expected dose given the nature of the 
geologic environment and anticipated performance of engineered barriers 
(see response to Issue 3 under Climate Change of this document). 
Specifying deep percolation assumptions in NRC regulations limits 
unbounded speculation concerning a narrow and discrete aspect of the 
overall performance assessment. Doing so does not determine either how 
DOE will apply that range of rates over the entire repository horizon 
or DOE's related analysis of the consequences for repository 
performance, much less constrain an NRC conclusion with respect to the 
acceptability of a potential application. Consequently, NRC does not 
consider its specification of the deep percolation rates or the data 
supporting it to be influential scientific information within the 
meaning of the OMB guidance.
    As discussed in relation to Climate Change issues 1 through 7 of 
this document, NRC's estimates of deep percolation are appropriate and 
well-supported. Based on public comment, the NRC has revised its 
specification for deep percolation values and provided additional 
clarification for the basis of the range of values (see Climate Change 
responses in this document). Further, these values are independent of 
any work or information provided by EPA or its contractors. With 
respect to the basis for the deep percolation rates, the NRC is not, as 
asserted by the State of Nevada, ``overwhelmingly relying on EPA 
information, including EPA's contractor documents'' in its calculations 
and judgments when the responsibility rests with NRC.

4. Use of Current Dosimetry

    Issue 1: Is the specification for using current methods of 
dosimetry and updated models for calculating potential radiation 
exposures sufficiently clear?
    Comment. DOE commented that the proposed approach for using current 
methods for dosimetry and updated models for dose calculations should 
be clarified in two specific areas. First, the definition for 
``weighting factor'' in the proposed regulation refers only to the 
tissue weighting factors provided in Appendix A of EPA's proposed 
standards and does not directly identify the radiation weighting 
factors also included in Appendix A. This definition should be expanded 
to include the radiation weighting factors specified in EPA's proposed 
standards. Second, Federal Guidance Report 13 is the current guidance 
report for estimating radiation doses; however, this report considers a 
slightly different set of organs than those included by EPA in Table 
A.2 (70 FR 49063), which represents the most current recommendations 
from the International Commission on Radiological Protection (ICRP). 
Clarification is needed on using current dosimetry methods because of 
the potential for differences in the list of organs considered in a 
particular method. Additionally, DOE suggested that one potential 
solution was for NRC to simply require that the calculation of doses be 
consistent with ICRP 60/72 methodology, use current scientific methods, 
and not provide any specific values in the regulation.
    Response. The definition for ``weighting factor'' for an organ or 
tissue in the proposed regulation states that ``the values'' in 
Appendix A of 40 CFR Part 197 are to be used for calculating the 
effective dose equivalent. This statement was intended to indicate that 
all the values in Appendix A (weighting factors for both radiation and 
for an organ or tissue) are to be used for calculating the effective 
dose equivalent. The Commission no longer considers it necessary to add 
a definition of the weighting factor in order to implement the values 
in Appendix A. Instead, the Commission clarifies the ``implementation'' 
of total effective dose equivalent (TEDE), specifically, the manner in 
which the values in Appendix A are to be used in dose calculations. The 
new text on the implementation of TEDE now states that the radiation 
and organ or tissue weighting factors in Appendix A are to be used in 
calculating the effective dose equivalent. Implementation of TEDE 
appears in the concepts section of Subpart E (Technical Criteria) in 
Part 63. Based on the added text on implementation of TEDE, the 
proposed definition for weighting factor is no longer necessary and has 
been removed in the final regulation.
    The Commission is aware that as dosimetry methods have advanced, 
additional organs have been considered in determining weighting factors 
and thus, there are differences in the lists of organs used in specific 
methods for estimating dose. The intent of the standards and 
regulations is to provide an approach for using currently accepted 
dosimetry methods and updated models for estimating radiation exposures 
and not for fixing a list of organs or tissues. The Commission 
considers currently accepted dosimetry methods to include those 
incorporated by EPA into federal radiation guidance as well as those 
included in 40 CFR Part 197, Appendix A. The Commission recognizes that 
the information presently available from consensus scientific 
organizations on newer dosimetric models (e.g., tabulations of 
calculated dose coefficients) differ for internal dose estimation 
relative to external dose estimation. Given this circumstance, use of 
external dosimetry methods in existing federal radiation guidance, 
Federal Guidance Report No. 12 (EPA, 1993), in combination with the 
more current internal dosimetry methods consistent with 40 CFR Part 
197, Appendix A, is an acceptable approach for calculating TEDE.

[[Page 10825]]

Whatever dosimetry method is used to estimate dose, it is expected that 
the calculation will consider the list of organs or tissues appropriate 
to that specific method. One way to clarify this issue would be to 
adopt the DOE suggestion to merely require that the calculation of 
doses be consistent with ICRP 60/72 methodology and use current 
scientific methods, and not provide any specific values in the 
regulation. Appendix A of the EPA Standards (73 FR 61256; October 15, 
2008) allows NRC to permit DOE to use revised weighting factors as 
updates are made in the future when these factors have been issued by a 
consensus of scientific organizations and incorporated by EPA into 
Federal radiation guidance. Rather than adopt the DOE suggestion that 
includes a reference to a specific methodology, the Commission 
considers it more appropriate to add text on implementing TEDE to:
    (1) Clarify that whatever methodology is adopted the weighting 
factors used in the calculation of dose are to be appropriate to the 
specific method;
    (2) Continue to refer to the values provided in Appendix A of the 
standards as the values that are presently considered to be current and 
appropriate; and
    (3) Prescribe the basis how DOE may be allowed to use newer methods 
and models.
    Thus, the regulations provide a consistency between the 
requirements for dose calculations and the scientific models and 
methodologies for calculating dose as scientific knowledge improves. 
Additionally, NRC's Regulatory Issue Summary 2003-04, ``Use of the 
Effective Dose Equivalent in Place of the Deep Dose Equivalent in Dose 
Assessments,'' provides further information on this topic.
    The implementation of TEDE is applicable in the context of dose 
calculations performed to demonstrate compliance with the requirements 
for a potential repository at Yucca Mountain.
    Issue 2: Should the definition for TEDE include clarification 
regarding how operational doses to workers are to be calculated?
    Comment. DOE commented that the definition of TEDE should clarify 
that assessing (monitoring) external exposure to workers during 
operations should use the deep-dose equivalent, whereas, potential 
external doses to workers in the future should be calculated using an 
effective dose equivalent. This clarification is necessary to resolve 
potential inconsistencies in the application of dose calculations 
between Parts 20 (i.e., monitored doses) and 63 (calculated doses).
    Response. Clarification regarding the monitoring of doses versus 
calculation of doses is essentially an issue of implementation of TEDE 
and is not one of redefining the term itself. Therefore, NRC is adding 
a separate discussion regarding implementation of TEDE in the concepts 
section of Subpart E (Technical Criteria) in Part 63 to provide the 
necessary clarification rather than modifying the definition of TEDE. 
The NRC is also revising the definition for TEDE in Part 63 to be 
consistent with the definition for TEDE in Part 20 to further clarify 
this is an issue of implementation of TEDE and not the definition of 
TEDE.
    As correctly stated in the comment, the deep-dose equivalent is an 
approach used for measuring external doses in the field, as is often 
done for demonstrating compliance with occupational exposures. The new 
text on implementation of TEDE clarifies that:
    (1) When the external exposure is determined by measurement with an 
external personal monitoring device, the deep dose equivalent is to be 
used instead of the effective dose equivalent, unless the effective 
dose equivalent is determined by a dosimetry method approved by the 
NRC;
    (2) The assigned deep-dose equivalent must be for the part of the 
body receiving the highest exposure; and
    (3) The assigned shallow-dose equivalent must be the dose averaged 
over the contiguous 10 square centimeters of skin receiving the highest 
exposure.
    The added text on implementation of TEDE provides the necessary 
clarification on how the deep-dose equivalent is to be used in 
determining compliance with the regulations for Yucca Mountain. 
Additionally, NRC's Regulatory Issue Summary 2003-04, ``Use of the 
Effective Dose Equivalent in Place of the Deep Dose Equivalent in Dose 
Assessments,'' provides further information on this topic.

5. Comments Beyond the Scope of This Rulemaking

    Some commenters submitted comments which are beyond the scope of 
this rulemaking as described in NRC's notice of proposed rulemaking. 
NRC responds to some of the concerns raised below. In addition, the 
State of Nevada requested that comments viewed as being beyond the 
scope of the rulemaking be considered as a petition for rulemaking. The 
State is familiar with NRC's process for considering petitions for 
rulemaking which is initiated by submittal of a petition under 10 CFR 
2.802 which meets the criteria of 10 CFR 2.802(c).
    Issue 1: Were intergovernmental meetings concerning the proposed 
EPA standards inappropriate?
    Comment. The State of Nevada and some other commenters suggested 
that non-public intergovernmental meetings at which EPA's proposed 
standards were discussed were somehow inappropriate and cast a cloud on 
EPA and NRC rules. These commenters cite no laws nor regulations 
barring such discussions but nevertheless assume that such meetings 
should not have taken place.
    Response. In the Nuclear Waste Policy Act of 1982, as amended 
(NWPA), Congress recognized the responsibility of the Federal 
Government to provide for the permanent disposal of HLW and spent 
nuclear fuel in order to protect public health and safety and the 
environment. Congress, in the NWPA and later in the EnPA, charged EPA 
and NRC with specific direction for developing standards and 
regulations for Yucca Mountain: EPA is to provide public health and 
radiation protection standards; NRC is to provide implementing 
regulations for those standards and is to consider a license 
application from DOE for the construction, operation, and closure of 
the repository at a site DOE has found suitable. It makes little sense 
for these agencies to act oblivious to the views of each other as to 
how protection of public health and safety and the environment with 
respect to a geologic repository can best be accomplished. It is both 
appropriate and important for NRC to be able to explain and discuss its 
regulatory approach in the context of the EPA standard with other 
Federal agencies. The State, in fact, recognizes this. In its comments, 
the State urged NRC to ``convince EPA to adopt a more reasonable and 
protective standard.''
    Although intergovernmental meetings are not normally open to the 
public, what is important is the fact that no ``secret'' decisions 
resulted from interagency discussions. Both the EPA's proposed 
standards and NRC's proposed regulations, including their rationale, 
were provided to the public for comment. After careful consideration of 
the public comments, both EPA and NRC have explained and documented 
their final standards and regulations, including how public comments 
were taken into account. The standards and regulations will stand or 
fall on the basis of the public record on which they rest, not on the 
basis of any discussions that may have taken place while the standards 
were being formulated.

[[Page 10826]]

    Issue 2: Should NRC provide additional requirements for defense-in-
depth?
    Comment. The State of Nevada believes that a meaningful defense-in-
depth standard is missing from the NRC rule. The State also suggested 
that a requirement pertaining to the expected performance of natural 
barriers would offer an essential protective feature for coping with 
early waste package failure (noting that the International Atomic 
Energy Agency (IAEA) has suggested that ``overall performance of the 
geologic disposal system shall not be unduly dependent on a single 
barrier or function'').
    Response. The Commission considers the approach for multiple 
barriers and defense-in-depth in Part 63 appropriate and protective. 
When NRC issued final Part 63 on November 2, 2001 (66 FR 55758), the 
Commission stated the goal of the current regulations regarding 
multiple barriers and defense-in-depth and explained its reasoning for 
not specifying requirements for specific barriers:

    The emphasis should not be on the isolated performance of 
individual barriers but rather on ensuring the repository system is 
robust, and is not wholly dependent on a single barrier. Further, 
the Commission supports an approach that would allow DOE to use its 
available resources effectively to achieve the safest repository 
without unnecessary constraints imposed by separate, additional 
subsystem performance requirements.
    It is also important to remember that part 63 requires DOE to 
carry out a performance confirmation program to provide further 
confidence that barriers important to waste isolation will continue 
to perform as expected (66 FR 55758).

The court addressed this same issue in Nevada's suit challenging the 
Part 63 rule:

    Specifically, Nevada contests NRC's use of defense-in-depth at 
the proposed Yucca Mountain repository through an overall system 
performance assessment rather than using the approach of its older 
regulations, which approach tests the individual performance of the 
repository's `system elements.' * * * In light of NRC's detailed 
analysis supporting its decision to evaluate the performance of the 
Yucca Mountain repository based on the barrier system's overall 
performance, we believe that it adequately explained its change in 
course. * * * Accordingly, we conclude that NRC acted neither 
arbitrarily nor capriciously in rejecting part 60's subsystem 
performance approach in favor of the overall performance approach. 
NEI v. EPA; 373 F.3d 1251, 1295-97

    (DC Cir. 2004).
    Issue 3: Should NRC disabuse EPA of its mistaken impression that 
there is some significant difference between ``reasonable assurance'' 
and ``reasonable expectation?''
    Comment. The State of Nevada asserted that NRC must disabuse EPA of 
its mistaken impression that there is some significant difference 
between the term ``reasonable assurance'' and the term ``reasonable 
expectation.''
    Response. As noted by the State, NRC and the State have already 
agreed that the two terms are substantially identical, see NEI v. EPA; 
373 F.3d 1251, 1301 (D.C. Cir. 2004).
    Issue 4: Should NRC prohibit DOE from relying on drip shields that 
may be installed in the distant future (e.g., 300 years from now)?
    Comment. The State of Nevada expressed concern that drip shields 
could be scheduled for installation many years in the future and, thus, 
there is no real guarantee that this safety feature will actually be 
installed. There is no reliable way to commit future decision-makers on 
this point. Therefore, NRC should not allow DOE to rely on the drip 
shields in demonstrating compliance with the post-closure performance 
objectives.
    Response. DOE must apply to NRC for authorization to build the 
proposed repository. Under NRC's regulations, DOE must show, among 
other things, that its proposal will comply with specified performance 
objectives for the geologic repository after permanent closure. On June 
3, 2008, DOE submitted a license application to NRC for authorization 
to construct a repository at Yucca Mountain. The NRC staff will 
evaluate whether DOE's proposed design, including reliance on any 
specific design feature or component of the engineered barrier system 
as described in the application, succeeds in making the required 
demonstration.
    The NRC staff will then document its assessment in a Safety 
Evaluation Report. If the NRC staff recommends that NRC authorize 
construction, the staff may specify potential license conditions, as 
needed, to provide reasonable expectation that relevant performance 
objectives will be met. NRC can only assess the need for such 
conditions, their reasonableness, and their potential to be enforced in 
the context of DOE's overall design as presented in a license 
application. If DOE proposes to install drip shields and if the drip 
shields are considered important for waste isolation or repository 
performance, the installation of the drip shield at an appropriate time 
would become part of the license conditions. At a later date, if DOE 
proposes not to install the drip shields, DOE would be obligated to 
seek specific regulatory approval in the form of a license amendment. 
Any NRC decision to grant or deny such an amendment request would be 
based on NRC's independent technical review and would be subject to a 
potential hearing as part of the amendment process.
    Issue 5: Should NRC incorporate into the final rule requirements 
for compliance monitoring and measures to be taken in the event of non-
compliance?
    Comment. Some commenters pointed out that NRC's proposed rule 
appears to be silent with regard to requirements for compliance 
monitoring and related measures to be taken if said monitoring 
demonstrates noncompliance with established standards. The commenters 
encouraged NRC to incorporate such requirements into the final rule.
    Response. Part 63 contains requirements for monitoring up to the 
time of permanent closure in Subpart F. Should the NRC grant the DOE a 
license to operate the repository, DOE must also provide a description 
of its program for post-permanent closure monitoring in its application 
to amend its license for permanent closure. See, Sec.  63.51(a)(2). The 
commenters' concerns regarding further monitoring and related measures 
can be considered at that time.
    Issue 6: Will adoption of the EPA standards necessitate revision of 
the ``S-3'' rule?
    Comment. The State of Nevada believes that NRC's adoption of EPA's 
standards with no added protections will require NRC to revisit its 
``S-3'' rule, 10 CFR 51.51, because this rule currently includes a 
``zero-release'' assumption that the long-term effects of disposing of 
spent fuel and HLW will be essentially zero because there would be no 
releases that would harm people or the environment after the repository 
is sealed. The State believes that this will no longer be the case if 
NRC adopts EPA's 3.5 mSv (350 mrem) standard for the post-10,000 year 
period.
    Response. As explained in the response to the comment on Issue 1 
under NRC Adoption of EPA Standards of this document, EnPA requires the 
Commission to modify its technical criteria to be consistent with EPA's 
standards for a geologic repository at the Yucca Mountain site. 
Moreover, the question whether the ``zero-release'' assumption of the 
S-3 rule may need to be revisited in the future is not presented in 
this rulemaking proceeding.

[[Page 10827]]

IV. Summary of Final Revisions

Section 63.2 Definitions

    The definition of ``performance assessment'' is revised to exclude 
the limitation of ``10,000 years after disposal,'' consistent with 
EPA's modified definition of ``performance assessment.'' The definition 
for ``total effective dose equivalent'' is revised to be consistent 
with Part 20.

Section 63.102 Concepts

    A discussion of the implementation of total effective dose 
equivalent (TEDE) is added to the concepts section to clarify how the 
weighting factors specified in EPA's final standards are to be used for 
calculating potential exposures.

Section 63.114 Requirements for Performance Assessment

    This section specifies the requirements for the performance 
assessment used to demonstrate compliance with the postclosure 
performance objectives. This section is revised to conform to EPA's 
final standards that specify what DOE must consider in the performance 
assessment for the period after 10,000 years i.e., the performance 
assessment methods meeting the existing requirements for the initial 
10,000 years are appropriate and sufficient for the period after 10,000 
years.

Section 63.302 Definitions for Subpart L

    The definition for the ``period of geologic stability'' is 
modified, consistent with EPA's final standards, to clarify that this 
period ends at 1 million years after disposal.

Section 63.303 Implementation of Subpart L

    This section provides a functional overview of this subpart. This 
section is revised to conform to EPA's final standard that specifies 
for the period after 10,000 years, the arithmetic mean of the estimated 
doses is to be used for determining compliance.

Section 63.305 Required Characteristics of the Reference Biosphere

    This section specifies characteristics of the reference biosphere 
to be used by DOE in its performance assessments to demonstrate 
compliance with the postclosure performance objectives specified at 
Sec.  63.113. This section is modified to conform to EPA's final 
standards, which specify the types of changes DOE must account for in 
the performance assessment for the period after 10,000 years and 
through the period of geologic stability.

Section 63.311 Individual Protection Standard After Permanent Closure

    This section specifies the dose limit for individual protection 
after permanent closure for any geologic repository at the Yucca 
Mountain site. This section is modified to conform with EPA's final 
standards for the peak dose after 10,000 years and through the period 
of geologic stability.

Section 63.321 Individual Protection Standard for Human Intrusion

    This section directs DOE to estimate the dose resulting from a 
stylized human intrusion drilling scenario and specifies the dose limit 
that any geologic repository at the Yucca Mountain site must meet as 
the result of a hypothetical human intrusion. This section is modified 
to conform with EPA's final standards for the peak dose after 10,000 
years and through the period of geologic stability.

Section 63.341 Projections of Peak Dose

    This section has been removed to be consistent with EPA's final 
standards.

Section 63.342 Limits on Performance Assessments

    This section specifies how DOE will identify and consider features, 
events, and processes in the dose assessments described in Subpart L to 
Part 63. This section is modified to conform to EPA's final standards 
that specify the types of changes DOE must account for in the 
performance assessment for the period after 10,000 years and through 
the period of geologic stability. A range and distribution for deep 
percolation rates are specified that DOE must use to represent the 
effects of climate change after 10,000 years and through the period of 
geologic stability. These criteria are substantially the same as those 
proposed by EPA and NRC with the exception of the constraint that 
requires DOE to consider, in its performance assessment, changes to the 
elevation of the water table under Yucca Mountain (i.e., water table 
rise) from a seismic event, which is included in the final regulations.

V. Agreement State Compatibility

    Under the ``Policy Statement on Adequacy and Compatibility of 
Agreement State Programs'' approved by the Commission on June 30, 1997, 
and published in the Federal Register on September 3, 1997 (62 FR 
46517), this rule is classified as Compatibility Category ``NRC.'' 
Compatibility is not required for Category ``NRC'' regulations. The NRC 
program elements in this category are those that relate directly to 
areas of regulation reserved to the NRC by the Atomic Energy Act of 
1954, as amended (AEA), or the provisions of Title 10 of the Code of 
Federal Regulations.

VI. Voluntary Consensus Standards

    The National Technology Transfer and Advancement Act of 1995 (Pub. 
L. 104-113) requires that Federal agencies use technical standards that 
are developed or adopted by voluntary consensus standards bodies unless 
the use of such a standard is inconsistent with applicable law or 
otherwise impractical. In this final rule, the NRC implements site-
specific standards proposed by EPA and developed solely for application 
to a proposed geologic repository for high-level radioactive waste at 
Yucca Mountain, Nevada. This action does not constitute the 
establishment of a standard that sets generally applicable 
requirements.

VII. Finding of No Significant Environmental Impact: Availability

    Under Section 121(c) of the Nuclear Waste Policy Act, this final 
rule does not require the preparation of an environmental impact 
statement under Section 102(2)(c) of the National Environmental Policy 
Act of 1969 (NEPA) or any environmental review under paragraphs (E) or 
(F) of Section 102(2) of NEPA.

VIII. Paperwork Reduction Act Statement

    This final rule does not contain new or amended information 
collection requirements subject to the Paperwork Reduction Act of 1995 
(44 U.S.C. 3501 et seq.). Existing requirements were approved by OMB, 
approval number 3150-0199.

Public Protection Notification

    NRC may not conduct nor sponsor, and a person is not required to 
respond to, a request for information nor an information collection 
requirement, unless the requesting document displays a currently valid 
OMB control number.

IX. Regulatory Analysis

    The Commission has prepared a regulatory analysis on this 
regulation. The analysis examines the costs and benefits of the 
alternatives considered by the Commission, consistent with the options 
that are available to NRC in carrying out the statutory directive of 
EnPA. The analysis is available for inspection in the NRC PDR, Room

[[Page 10828]]

O1F21, One White Flint North, 11555 Rockville Pike, Rockville, MD.

X. Regulatory Flexibility Certification

    Under the Regulatory Flexibility Act of 1980 (5 U.S.C. 605(b)), the 
Commission certifies that this rule does not have a significant 
economic impact on a substantial number of small entities. This rule 
affects the licensing of only one entity, DOE, which does not fall 
within the scope of the definition of ``small entities'' set forth in 
the Regulatory Flexibility Act or the Small Business Size Standards set 
out in regulations issued by the Small Business Administration at 13 
CFR Part 121.

XI. Backfit Analysis

    The NRC has determined that the backfit rule (Sec. Sec.  50.109, 
70.76, 72.62, or 76.76) does not apply to this final rule because this 
amendment does not involve any provisions that would impose backfits as 
defined in the backfit rule. Therefore, a backfit analysis is not 
required.

XII. Congressional Review Act

    Under the Congressional Review Act of 1996, the NRC has determined 
that this action is not a major rule and has verified this 
determination with the Office of Information and Regulatory Affairs of 
OMB.

List of Subjects in 10 CFR Part 63

    Criminal penalties, High-level waste, Nuclear power plants and 
reactors, Reporting and recordkeeping requirements, Waste treatment and 
disposal.


0
For the reasons set out in the preamble and under the authority of the 
Atomic Energy Act of 1954, as amended; the Energy Reorganization Act of 
1974, as amended; the Nuclear Waste Policy Act of 1982, as amended; and 
5 U.S.C. 552 and 553; the NRC is adopting the following amendments to 
10 CFR Part 63.

PART 63--DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTES IN A GEOLOGIC 
REPOSITORY AT YUCCA MOUNTAIN, NEVADA

0
1. The authority citation for part 63 continues to read as follows:

    Authority: Secs. 51, 53, 62, 63, 65, 81, 161, 182, 183, 68 Stat. 
929, 930, 932, 933, 935, 948, 953, 954, as amended (42 U.S.C. 2071, 
2073, 2092, 2093, 2095, 2111, 2201, 2232, 2233); secs. 202, 206, 88 
Stat. 1244, 1246 (42 U.S.C. 5842, 5846); secs. 10 and 14, Pub. L. 
95-601, 92 Stat. 2951 (42 U.S.C. 2021a and 5851); sec. 102, Pub. L. 
91-190, 83 Stat. 853 (42 U.S.C. 4332); secs. 114, 121, Pub. L. 97-
425, 96 Stat. 2213g, 2238, as amended (42 U.S.C. 10134, 10141); and 
Pub. L. 102-486, sec. 2902, 106 Stat. 3123 (42 U.S.C. 5851); sec. 
1704, 112 Stat. 2750 (44 U.S.C. 3504 note).


0
2. Section 63.2 is amended by revising paragraph (1) of the definition 
of ``performance assessment'' and revising the definition of ``total 
effective dose equivalent (TEDE)'' to read as follows:


Sec.  63.2   Definitions.

* * * * *
    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;
* * * * *
    Total effective dose equivalent (TEDE) means the sum of the 
effective dose equivalent (for external exposures) and the committed 
effective dose equivalent (for internal exposures).
* * * * *

0
3. In Sec.  63.102 paragraph (o) is added to read as follows:


63.102  Concepts.

* * * * *
    (o) Implementation of TEDE. When external exposure is determined by 
measurement with an external personal monitoring device, the deep-dose 
equivalent must be used in place of the effective dose equivalent, 
unless the effective dose equivalent is determined by a dosimetry 
method approved by the NRC. The assigned deep-dose equivalent must be 
for the part of the body receiving the highest exposure. The assigned 
shallow-dose equivalent must be the dose averaged over the contiguous 
10 square centimeters of skin receiving the highest exposure. The 
radiation and organ or tissue weighting factors in Appendix A of 40 CFR 
part 197 are to be used to calculate TEDE. After the effective date of 
this regulation, the Commission may allow DOE to use updated factors, 
which have been issued by consensus scientific organizations and 
incorporated by EPA into Federal radiation guidance. Additionally, as 
scientific models and methodologies for estimating doses are updated, 
DOE may use the most current and appropriate (e.g., those accepted by 
the International Commission on Radiological Protection) scientific 
models and methodologies to calculate the TEDE. The weighting factors 
used in the calculation of TEDE must be consistent with the methodology 
used to perform the calculation.


0
4. Section 63.114 is revised to read as follows:


63.114  Requirements for performance assessment.

    (a) Any performance assessment used to demonstrate compliance with 
Sec.  63.113 for 10,000 years after disposal must:
    (1) Include data related to the geology, hydrology, and 
geochemistry (including disruptive processes and events) of the Yucca 
Mountain site, and the surrounding region to the extent necessary, and 
information on the design of the engineered barrier system used to 
define, for 10,000 years after disposal, parameters and conceptual 
models used in the assessment.
    (2) Account for uncertainties and variabilities in parameter 
values, for 10,000 years after disposal, and provide for the technical 
basis for parameter ranges, probability distributions, or bounding 
values used in the performance assessment.
    (3) Consider alternative conceptual models of features and 
processes, for 10,000 years after disposal, that are consistent with 
available data and current scientific understanding and evaluate the 
effects that alternative conceptual models have on the performance of 
the geologic repository.
    (4) Consider only features, events, and processes consistent with 
the limits on performance assessment specified at Sec.  63.342.
    (5) Provide the technical basis for either inclusion or exclusion 
of specific features, events, and processes in the performance 
assessment. Specific features, events, and processes must be evaluated 
in detail if the magnitude and time of the resulting radiological 
exposures to the reasonably maximally exposed individual, or 
radionuclide releases to the accessible environment, for 10,000 years 
after disposal, would be significantly changed by their omission.
    (6) Provide the technical basis for either inclusion or exclusion 
of degradation, deterioration, or alteration processes of engineered 
barriers in the performance assessment, including those processes that 
would adversely affect the performance of natural barriers. 
Degradation, deterioration, or alteration processes of engineered 
barriers must be evaluated in detail if the magnitude and time of the 
resulting radiological exposures to the reasonably maximally exposed 
individual, or radionuclide releases to the accessible environment, for 
10,000 years after disposal, would be significantly changed by their 
omission.
    (7) Provide the technical basis for models used to represent the 
10,000

[[Page 10829]]

years after disposal in the performance assessment, such as comparisons 
made with outputs of detailed process-level models and/or empirical 
observations (e.g., laboratory testing, field investigations, and 
natural analogs).
    (b) The performance assessment methods used to satisfy the 
requirements of paragraph (a) of this section are considered sufficient 
for the performance assessment for the period of time after 10,000 
years and through the period of geologic stability.


0
5. In Sec.  63.302, the definition of ``period of geologic stability'' 
is revised to read as follows:


63.302  Definitions for Subpart L.

* * * * *
    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
6. Section 63.303 is revised to read as follows:


63.303   Implementation of Subpart L.

    (a) Compliance is 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 63.311(a)(1) and 63.311(a)(2); and
    (2) Sections 63.321(b)(1), 63.321(b)(2), and 63.331, if performance 
assessment is used to demonstrate compliance with either or both of 
these sections.


0
7. Section 63.305, paragraph (c) is revised to read as follows:


63.305  Required characteristics of the reference biosphere.

* * * * *
    (c) 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.  63.342.
* * * * *

0
8. Section 63.311 is revised to read as follows:


Sec.  63.311  Individual protection standard after permanent closure.

    (a) 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 dose from 
releases from the undisturbed Yucca Mountain disposal system:
    (1) 0.15 mSv (15 mrem) for 10,000 years following disposal; and
    (2) 1.0 mSv (100 mrem) after 10,000 years, but within the period of 
geologic stability.
    (b) DOE's performance assessment must include all potential 
pathways of radionuclide transport and exposure.

0
9. Section 63.321 is revised to read as follows:


Sec.  63.321  Individual protection standard for human intrusion.

    (a) DOE must determine the earliest time after disposal that the 
waste package would degrade sufficiently that a human intrusion (see 
Sec.  63.322) could occur without recognition by the drillers.
    (b) DOE must demonstrate that there is a reasonable expectation 
that the reasonably maximally exposed individual receives, as a result 
of the human intrusion, no more than the following annual dose:
    (1) 0.15 mSv (15 mrem) for 10,000 years following disposal; and
    (2) 1.0 mSv (100 mrem) after 10,000 years, but within the period of 
geologic stability.
    (c) DOE's analysis must include all potential environmental 
pathways of radionuclide transport and exposure, subject to the 
requirements of Sec.  63.322.


Sec.  63.341  [Removed]

0
10. Section 63.341 is removed.
0
11. Section 63.342 is revised to read as follows:


Sec.  63.342  Limits on performance assessments.

    (a) DOE's performance assessments conducted to show compliance with 
Sec. Sec.  63.311(a)(1), 63.321(b)(1), and 63.331 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. In addition, DOE's performance assessments need 
not evaluate the impacts resulting from any 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.
    (b) For performance assessments conducted to show compliance with 
Sec. Sec.  63.321(b)(1) and 63.331, DOE's performance assessments shall 
exclude the unlikely features, events, and processes, or sequences of 
events and processes, i.e., those that are estimated to have less than 
one chance in 100,000 per year of occurring and at least one chance in 
100,000,000 per year of occurring.
    (c) For performance assessments conducted to show compliance with 
Sec. Sec.  63.311(a)(2) and 63.321(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. DOE 
must evaluate all of the features, events, or processes included in 
paragraph (a) of this section, and also:
    (1) DOE must assess the effects of seismic and igneous activity 
scenarios, subject to the probability limits in paragraph (a) of this 
section for very unlikely features, events, and processes, or sequences 
of events and processes. Performance assessments conducted to show 
compliance with Sec.  63.321(b)(2) are also subject to the probability 
limits in paragraph (b) of this section for unlikely features, events, 
and processes, or sequences of events and processes.
    (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 
(i.e., the magnitude of the water table rise under Yucca Mountain).
    (ii) The igneous activity 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) 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-
in-time climate conditions. The analysis may commence at 10,000 years 
after disposal and shall extend through the period of geologic 
stability. The constant-in-time values to be used to represent climate 
change are to be the spatial average of the deep percolation rate 
within the area bounded by the repository footprint. The constant-in-
time deep percolation rates to be used to represent climate change 
shall be based on a lognormal distribution with an arithmetic mean of 
41 mm/year (1.6 in./year) and a standard deviation of 33 mm/year (1.3 
in./year). The lognormal

[[Page 10830]]

distribution is to be truncated so that the deep percolation rates vary 
between 10 and 100 mm/year (0.39 and 3.9 in./year).
    (3) DOE must assess the effects of general corrosion on engineered 
barriers. 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.

    Dated at Rockville, Maryland, this 9th day of March 2009.

    For the Nuclear Regulatory Commission.
Annette L. Vietti-Cook,
Secretary of the Commission.
[FR Doc. E9-5448 Filed 3-12-09; 8:45 am]
BILLING CODE 7590-01-P


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