[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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Rules and Regulations
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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.
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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 [email protected].
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
[email protected]; Janet Kotra, Office of Nuclear Material
Safety and Safeguards, U.S. Nuclear Regulatory Commission, Washington,
DC 20555-0001, telephone (301) 492-3190, e-mail [email protected]; 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
[email protected].
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