[Federal Register Volume 67, Number 195 (Tuesday, October 8, 2002)]
[Rules and Regulations]
[Pages 62628-62634]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-25521]
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NUCLEAR REGULATORY COMMISSION
10 CFR Part 63
RIN 3150-AG91
Specification of a Probability for Unlikely Features, Events and
Processes
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
[[Page 62629]]
potential geologic repository at Yucca Mountain, Nevada, to define the
term ``unlikely'' in quantitative terms. NRC regulations now specify a
range of numerical values for use in determining whether a feature,
event or process, or a sequence of events and processes, should be
excluded from certain required assessments. NRC is taking this action
to clarify how it plans to implement two of the environmental standards
for Yucca Mountain issued by the U.S. Environmental Protection Agency
(EPA). Specifically, EPA's standards require the exclusion of
``unlikely'' features, events or processes, or sequences of events and
processes, from the required assessments for the human-intrusion and
ground-water protection standards. In accordance with the Energy Policy
Act of 1992, NRC has adopted EPA's standards in its recently published
technical requirements for a potential geologic repository at Yucca
Mountain.
EFFECTIVE DATE: November 7, 2002.
ADDRESSES: The final rule and any related documents are available on
NRC's rulemaking Web site at http://ruleforum.llnl.gov. For information
about the interactive rulemaking Web site, contact Carol Gallagher
(301) 415-5905; e-mail nrc.gov">cag@nrc.gov.
The documents may also be examined at the NRC Public Document Room
(PDR), Room O-1F23, 11555 Rockville Pike, Rockville, MD.
NRC maintains an Agencywide Document Access and Management System
(ADAMS), which provides text and image files of NRC's public documents.
These documents may be accessed through NRC's Public Electronic Reading
Room on the Internet at http://www.nrc.gov/reading-rm/adams.html. If
you do not have access to ADAMS, or if there are problems in accessing
the documents located in ADAMS, contact the NRC PDR Reference staff at
1-800-397-4209, or 301-415-4737; or by e-mail to: nrc.gov">pdr@nrc.gov.
FOR FURTHER INFORMATION CONTACT: Timothy McCartin, Office of Nuclear
Material Safety and Safeguards, U.S. Nuclear Regulatory Commission,
Washington, DC 20555-0001, telephone (301) 415-7285, e-mail:
nrc.gov">tjm3@nrc.gov; or Clark Prichard, Office of Nuclear Material Safety and
Safeguards, U.S. Nuclear Regulatory Commission, Washington, DC 20555-
0001, telephone (301) 415-6203, e-mail: nrc.gov">cwp@nrc.gov.
SUPPLEMENTARY INFORMATION:
I. Background
On November 2, 2001 (66 FR 55732), NRC published a final rule, 10
CFR part 63, governing disposal of high-level radioactive wastes in a
potential geologic repository at Yucca Mountain, Nevada. We are now
finalizing one particular matter that specifies a probability for
unlikely features, events, and processes (FEPs). These are the
regulations that the U.S. Department of Energy (DOE) must meet in any
license application for construction and operation of a potential
repository. As mandated by the Energy Policy Act of 1992, Pub. L. 102-
486, NRC's rule adopts the radiation protection standards established
by EPA in 40 CFR Part 197 (66 FR 32074; June 13, 2001). EPA's standards
for disposal include an individual-protection standard (40 CFR 197.20);
a human-intrusion standard (40 CFR 197.25); and ground-water protection
standards (40 CFR 197.30). These EPA standards have been incorporated
into NRC's regulations at 10 CFR 63.311, 63.321, and 63.331,
respectively.
DOE's performance assessments are required to consider the
naturally occurring features, events, and processes that could affect
the performance of a geologic repository (i.e., specific conditions or
attributes of the geologic setting; degradation, deterioration, or
alteration processes of engineered barriers; and interactions between
natural and engineered barriers). EPA's standards include limits on
what DOE must consider in performance assessments undertaken to
determine whether the repository will perform in compliance with the
standards (40 CFR 197.36). EPA's standards state that DOE's performance
assessments shall not include consideration of ``very unlikely'' FEPs,
which EPA defines to be those FEPs that are estimated to have less than
one chance in 10,000 of occurring within 10,000 years of disposal. In
addition, EPA's standards require NRC to exclude ``unlikely'' FEPs, or
sequences of events and processes, from the required assessments for
demonstrating compliance with the human-intrusion and ground-water
protection standards. EPA did not define unlikely FEPs in its
standards, but, rather, left the specific probability of the unlikely
FEPs for NRC to define. The Commission explained in its rulemaking
establishing part 63 that it `` * * * fully supports excluding unlikely
FEPs from analyses for estimating compliance with the standards for
human intrusion and ground-water protection * * *,'' and that it ``* *
* plan[ned] to conduct an expedited rulemaking to quantitatively define
the term `unlikely''' (66 FR 55734; November 2, 2001).
NRC published a proposed rule, ``10 CFR Part 63: Specification of a
Probability for Unlikely Features, Events, and Processes,'' on January
25, 2002 (67 FR 3628), and requested public comments. That proposed
rule defined the term ``unlikely'' in quantitative terms. This action
was taken to allow NRC to implement EPA's final standards for a
potential repository at Yucca Mountain, Nevada. The Commission was
careful to point out that its specification for unlikely events was in
the context of very specific assessments (i.e., those made to assess
compliance with ground-water protection and human-intrusion standards)
over a long time frame, and this specification was not intended to
suggest or imply precedent for other significantly different
applications that used the term ``unlikely'.
Unlike the broader purposes served by the performance assessment
for the all-pathway individual-protection standard, the performance
assessments used to determine compliance with the human-intrusion
standard and the ground-water protection standards serve narrow,
focused objectives. In the case of the performance assessment for human
intrusion, the purpose is to evaluate the robustness of the repository
system, assuming the occurrence of a prescribed human-intrusion
scenario. In the case of the performance assessment for ground-water
protection, the purpose is to evaluate potential degradation of the
ground-water resource. Although EPA's final standards did not specify a
numerical value to define unlikely FEPs in quantitative terms, the
preamble to the standards stated that the exclusion of unlikely FEPs is
intended to focus these assessments on the ``expected'' or ``likely''
performance of the repository.\1\
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\1\ For example, the preamble states: (1) ``[T]he assessment of
resource pollution potential is based upon the engineering design of
the repository being sufficiently robust under expected conditions
to prevent unacceptable degradation of the ground-water resource
over time'' (66 FR 32114; June 13, 2001); and (2) the term
``undisturbed,'' which is used in connection with demonstrating
compliance with the ground-water protection standards, means the ``*
* * * disposal system is not disturbed by human intrusion but that
other processes or events that are likely to occur could disturb the
system'' (66 FR 32104; June 13, 2001).
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From a probabilistic perspective, any FEP with an annual
probability of 10-4 or higher would have a high probability
of occurring within the 10,000 year compliance period.\2\ As the
Commission
[[Page 62630]]
described in the proposed rule, likely FEPs should include not only
FEPs very likely to occur, but also those reasonably likely to occur.
Given uncertainties in estimating the occurrence of FEPs over a 10,000
year time period, the Commission believed a prudent decision was to
consider FEPs with 10 percent or greater chance of occurring within the
10,000 year compliance period as likely FEPs. Thus, the Commission
sought public comment on its proposal that unlikely FEPs be defined as
those FEPs with less than a 10 percent chance, but greater than or
equal to a 0.01 percent chance, of occurring within the 10,000 year
compliance period (i.e., annual probability less than 10-5,
but greater than or equal to 10-8, which is the upper
boundary for very unlikely events). As mentioned previously, the focus
of the performance assessments for human intrusion and ground-water
protection is to be on expected conditions. The Commission believes an
upper bound for unlikely FEPs of a 10 percent chance of occurring
within the compliance period will focus the assessments for ground-
water protection and human intrusion on the likely performance of the
repository.
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\2\ Estimating a high probability of occurrence for an FEP
creates an expectation that an FEP will occur; however, it does not
guarantee such an occurrence. There is a chance that even high-
probability FEPs will not occur. Likewise, in a probabilistic sense,
having a low probability of occurrence does not mean that an FEP
will not occur.
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II. Public Comments and Responses
The 75-day comment period for the proposed rule closed on April 10,
2002. Comments were received from the following five organizations:
EPA; State of Nevada and the Nevada Agency for Nuclear Projects; DOE;
Nuclear Energy Institute (NEI); and Exelon Generation. Commenters
differed on the quantitative values NRC should use for defining
unlikely FEPs. Although some commenters supported the proposed values,
others provided different numbers and associated rationales. In
preparing the final rule, the NRC staff carefully reviewed and
considered these comments. The commenters that suggested alternative
values did not provide a convincing basis for rejecting NRC's proposed
range and adopting a different range; therefore, the Commission has
decided to finalize the rule as originally proposed. The NRC's
consideration of each of the comments is provided below.
1. EPA Comments
Comment 1.1: The upper value for the probability range for unlikely
FEPs should be an annual probability of 10-6. An annual
probability of 10-6 as a demarcation separating likely FEPs
from unlikely FEPs is reasonable because it is the middle of the range
between FEPs that are nearly certain to occur (i.e., annual probability
of 10-4), and FEPs that are very unlikely to occur (i.e.,
annual probability of 10-8). Placing the demarcation closer
to either end of the range could be perceived as biased, either too
liberal or too conservative, whereas the middle of the range avoids
those implications. The NRC proposal, which is a factor of 10 reduction
(from the 10-4 annual probability level), could be perceived
as an arbitrary selection, whereas an annual probability of
10-6 is a factor of 100 reduction and is likely to be more
widely accepted.
Response 1.1: The Commission stated in the proposed rulemaking (67
FR 3629; January 25, 2002) that the specification of a value to
quantitatively define the probability for unlikely FEPs is complicated
because of the subjective nature of the term ``unlikely.'' The
Commission did consider the merits of using an annual probability of
10-6 rather than 10-5 for the demarcation between
likely and unlikely FEPs. These two probability values represent
approximately a 1 percent and 10 percent chance of occurring over the
10,000 year regulatory period. The Commission considered a 1 percent
chance of occurring (i.e., annual probability of 10-6 over
10,000 years) neither expected nor likely and, therefore, an
inappropriate value for the demarcation between likely and unlikely
FEPs (67 FR 3630; January 25, 2002). The Commission continues to
believe an annual probability of 1 x 10-5 (i.e., 10 percent
chance of occurring within the 10,000 year compliance period) is a
protective and prudent value for defining the upper limit of unlikely
FEPs and is retaining the proposed range for defining unlikely FEPs.
EPA has suggested that a probability value which represents the
middle of a particular range (only when displayed on a logarithmic
scale) contains some inherent justification for its selection. EPA also
suggests that the NRC proposal, which is a factor of 10 less than an
annual probability of 10-4, may be considered too high by
some, whereas the EPA recommended value of 10-6, which is
100 times lower than 10-4, is likely to be more acceptable.
The issue is not whether a particular value lies within the middle of a
range (when plotted in a particular manner), or that the value is 10
rather than 100 times less than another value. The issue for NRC is to
determine an appropriate value that is protective of public health and
safety and the environment, and consistent with EPA's standards. EPA's
standards exclude unlikely FEPs from the required assessments for
ground-water protection and human intrusion so that these assessments
may focus on the likely performance of the repository. This is the
context in which the definition of a specific probability value should
be viewed. The Commission and other commenters consider the NRC
proposal (i.e., 10 percent chance of occurring over 10,000 years
defines demarcation between likely and unlikely FEPs) consistent with
the intended focus of the assessments for ground-water protection and
human intrusion, and protective of public health and safety and the
environment (see Comments 3-5).
Comment 1.2: Given the significant uncertainty in estimating the
probability for rare events (e.g., events with an annual probability of
10-5), specification of an annual probability value of
10-6 for the demarcation between likely and unlikely FEPs
will provide greater confidence that all likely FEPs are considered in
the assessments for ground-water protection and human intrusion. There
is no need to be restrictive about the probability limits because both
standards and regulations allow for excluding FEPs that have no
significant impact on performance results. Use of an annual probability
of 10-6 assures a reasonably conservative approach is taken
for screening FEPs.
Response 1.2: EPA has suggested that the Commission adopt a more
conservative approach for selecting the demarcation between likely and
unlikely FEPs. The Commission disagrees with this approach advocated by
EPA for the following reasons: (1) The proposed value of
10-5 (i.e., 10 percent chance of occurrence over 10,000
years) already represents a reasonably conservative value for the
demarcation between likely and unlikely FEPs; (2) introducing
additional conservatism for screening of FEPs, by selecting an annual
probability of 10-6, will detract from the intended purpose
of the assessments to focus on likely performance; and (3)
understanding and addressing uncertainties in the quantitative
estimates for the probabilities of FEPs is preferred over selection of
more conservative screening values.
The Commission acknowledges that selection of a more conservative
value (i.e., annual probability of 10-6) for the demarcation
between likely and unlikely FEPs could provide additional assurance by
considering a broader range of FEPs. Such an approach, however, would
not be consistent with the intent that the required assessments focus
on likely behavior. EPA, in
[[Page 62631]]
describing what level of expectation will meet the standards, has
pointed out negative aspects of an overly conservative approach (e.g.,
conservatism can bias analyses and deflect attention from questions
critical to developing an adequate understanding of the FEPs) (66 FR
32102; June 13, 2001). The Commission understands that EPA believes its
recommendation (i.e., annual probability of 10-6) is
``reasonably'' conservative. However, the Commission views EPA's
recommendation, which would identify FEPs with as little as a one-in-a-
million chance of occurring in a year (i.e., one percent chance of
occurring over 10,000 years) as likely FEPs, as overly conservative and
thus not appropriate. The Commission, as well as other commenters (see
Comments 4 and 5), support the annual probability of 10-5
(i.e., 10 percent chance of occurrence over 10,000 years) as a
reasonably conservative value for the demarcation between likely and
unlikely FEPs. The Commission continues to believe the specification of
an annual probability of 10-5 is consistent with the focus
on likely performance for the assessments of ground-water protection
and human intrusion.
There will be uncertainty in estimating performance of any geologic
repository, including the uncertainty in estimating the probabilities
of FEPs. NRC's regulation for Yucca Mountain contains specific
requirements for addressing uncertainty in estimating performance,
which includes uncertainty for estimating probabilities for FEPs. The
Commission believes it is prudent to understand and evaluate the
uncertainty in the probability estimates rather than set a more
conservative screening value as a means to address uncertainty in
estimating probabilities of FEPs. Reasonable expectation, as specified
in EPA standards (40 CFR 197.14) and NRC regulations (10 CFR 63.304),
in compliance with the postclosure standards of the repository,
dictates that uncertainties be understood and evaluated even when they
may be difficult to precisely quantify (e.g., accounting for the
inherently greater uncertainties, in making long-term projections of
the performance of the Yucca Mountain disposal system, does not exclude
important parameters from assessments and analyses simply because they
are difficult to precisely quantify to a high degree of confidence). In
the preamble to the final standards, EPA asserted that ``[T]he
reasonable expectation approach is aimed simply at focusing attention
on understanding the uncertainties in projecting disposal system
performance so that regulatory decision making will be done with a full
understanding of the uncertainties involved'' (66 FR 32102; June 13,
2001). The Commission believes its requirements for the performance
assessments provide for a thorough evaluation and understanding of
uncertainties in estimating repository performance. Thus, selection of
a more conservative probability value for the demarcation between
likely and unlikely FEPs is unnecessary. As discussed previously, the
Commission continues to believe the proposed value (i.e., 10 percent
chance of occurring within 10,000 years) ensures the assessments for
ground-water protection and human intrusion focus, as intended, on
likely performance, whereas the use of more conservative values to
define unlikely FEPs would inappropriately distort the estimation of
likely performance.
Comment 1.3: Variation in dose assessments for Yucca Mountain is
sufficiently broad (e.g., two orders of magnitude--a factor of one-
hundred) that it is reasonable to adopt an annual probability value of
10-6 as the demarcation between likely and unlikely FEPs
because this value represents a numerically similar difference (i.e.,
two orders of magnitude) between it and the probability for events
nearly certain to occur within the 10,000 year period (i.e., an annual
probability value of 10-4). Whereas NRC's proposed value
(i.e., an annual probability value of 10-5) is only a factor
of 10 (i.e., one order of magnitude) different from the probability for
events nearly certain to occur.
Response 1.3: The performance assessments for evaluating individual
protection for the proposed repository at Yucca Mountain evaluate
performance probabilistically; therefore, the estimates of repository
performance are represented by a range of values. The variation in
repository performance results from including uncertainty and
variability in the models and parameters of the performance assessment
used to represent FEPs associated with the site conditions and the
natural and engineered barriers of the repository. EPA's observation
that the variation in estimates of repository performance and the
difference between the EPA recommendation of an annual probability
value of 10-6 and the probability of FEPs nearly certain to
occur within the 10,000 year period (i.e., an annual probability value
of 10-4) are both two orders of magnitude does not justify
EPA's recommendation, nor does it imply that NRC's proposed value of
10-5 is inappropriate. EPA has not provided information to
support the relevance of this observation to the specification of a
value for the demarcation of likely and unlikely FEPs. The performance
assessments for Yucca Mountain involve complex models, for FEPs, that
consider the uncertainty and variability in natural processes and the
degradation of engineered materials. Performance assessments are
expected to continue to evolve over time as new information is
collected and evaluated and the variation in performance assessment
results is also expected to change. A logical conclusion of the EPA
comment is that the demarcation between likely and unlikely FEPs should
change if future assessments of Yucca Mountain cause the variation of
results to deviate from the current two orders of magnitude range. The
Commission believes the determination of an annual probability for the
demarcation between likely and unlikely FEPs should not be tied to the
performance assessment results nor any other particular assessment of
site conditions (see also response to Comment 1.4).
Comment 1.4: The selection of the probability for the demarcation
between likely and unlikely FEPs should be divorced from the site
conditions.
Response 1.4: The Commission agrees that site conditions should not
be used to determine the probability for the demarcation between likely
and unlikely FEPs. NRC's proposed rulemaking did not use any site
conditions to determine an appropriate probability value. In the
proposed rule, the Commission did identify a few selected FEPs, as a
matter of reference, to inform the public of the kinds of FEPs that
might be included and excluded by the proposed probability range for
unlikely FEPs (67 FR 3630; January 25, 2002).
2. State of Nevada and the Nevada Agency for Nuclear Projects Comments
Comment 2.1: Unlikely FEPs should be defined by the same
quantitative value used to define very unlikely FEPs (i.e., annual
probability less than 10-8). The EPA standard requires the
Commission to set the quantitative level for unlikely FEPs, but it does
not require that it be higher than the value used to define very
unlikely FEPs.
Response 2.1: The EPA standards provide that a numerical value to
define unlikely FEPs is to be specified by NRC, and the preamble to the
standards clearly indicates that any such value would be higher than
the value used to define very unlikely events. More
[[Page 62632]]
specifically, the preamble to the final standards states: ``[W]e
intended to establish another demarcation for excluding unlikely
features, events, and processes with a higher probability. * * *'' (66
FR 32100; June 13, 2002). The Commission does not consider the State's
proposal (i.e., unlikely FEPs be specified with the same numerical
value used to define very unlikely FEPs) consistent with EPA's intent
for the standards or common understanding of the two terms ``unlikely''
and ``very unlikely,'' which imply a difference in likelihood. The
Commission believes its proposal, which specified a numerical range for
unlikely FEPS above the range for very unlikely FEPs, is consistent
with the EPA standards, as required by statute, and is fully protective
of public health and safety and the environment.
Comment 2.2: Preservation of ground-water quality must not be
compromised. Therefore, the assessment for protection of ground water
should be no less rigorous than the assessment used to evaluate
individual protection, which is required to consider unlikely events.
Response 2.2: The State is correct in pointing out that the
individual protection assessment is the only assessment that includes
unlikely FEPs; however, the EPA standards are clear that ``unlikely''
FEPs are to be excluded from the performance assessments for ground-
water protection and human intrusion (40 CFR 197.36). The State of
Nevada's recommendation is not consistent with EPA's standards that
specify different assessments for determining compliance with the
ground-water protection and individual-protection standards. EPA's
intent for the assessments for ground-water protection and human
intrusion is to focus on the likely performance of the repository;
thus, unlikely events are to be excluded from these two assessments
(see Response 1.2). Unlikely FEPs should not be included in the
assessments for ground-water protection and human intrusion, because
inclusion would inappropriately emphasize the contribution of these
less likely FEPs when determining the likely behavior of the
repository. Exclusion of low-probability FEPs ensures that the
assessments for ground-water protection and human intrusion are as
intended (i.e., on likely repository performance).
Ground water is an important resource, and potential contamination
of ground water is evaluated in all three assessments (i.e., ground-
water protection, human intrusion, and individual protection) required
by regulations and standards. More specifically, the assessment for
ground-water protection must demonstrate compliance with stringent
safety standards [e.g., 0.04 millisievert/year (mSv/yr) (4 millirem/
year (mrem/yr))] for the potential contamination of drinking water. The
assessment for individual protection must demonstrate compliance with a
0.15 mSv/yr (15 mrem/yr) exposure limit from all potential exposure
pathways (e.g., drinking contaminated water, consuming crops that are
assumed to be irrigated with contaminated water, consuming animal
products that are assumed to be raised with contaminated water and
feed) and include unlikely FEPs. The assessment for human intrusion
must demonstrate compliance with a 0.15 mSv/yr (15 mrem/yr) exposure
limit from all potential exposure pathways, and assume that a human
intrusion results in a borehole that provides a direct pathway for
water to transport waste to the water table (i.e., the ground-water
resource). The Commission considers the multiple and overlapping
assessments for ground-water protection, individual protection, and
human intrusion, and the associated standards, to provide a
comprehensive evaluation of potential ground-water contamination that
is protective of the ground-water resource. Requiring the assessments
for ground-water protection and human intrusion to include ``unlikely''
FEPs is not necessary for protection of the ground-water resource nor
consistent with the EPA standards.
Comment 2.3: NRC's proposed value for unlikely events would, but
should not, allow the exclusion of igneous activity from consideration
in the performance assessments for ground-water protection and human
intrusion because it could be the largest contributor to dose. The
proposed definition for unlikely events is subjective to the extreme
because the largest risk contributor is excluded.
Response 2.3: The State's recommendation that igneous activity be
included because, as currently assessed, igneous activity is the
largest contributor to risk, is not consistent with EPA's standards.
EPA's standards specify that NRC is to determine FEPs are either
``unlikely'' or ``very unlikely,'' based on the likelihood of
occurrence of the FEPs and not on other considerations, such as risk.
The Commission explained, in its proposed rule (67 FR 3629; January 25,
2002), that EPA's intent for the assessments for ground-water
protection and human intrusion was to focus on the likely performance
of the repository; thus, unlikely events are to be excluded from these
two assessments. Unlikely FEPs should not be included in the
assessments for ground-water protection and human intrusion because
inclusion would inappropriately emphasize the contribution of these
less likely FEPs when determining the likely behavior of the
repository. Exclusion of such low-probability FEPs ensures that the
assessments for ground-water protection and human intrusion are as
intended (i.e., on likely repository performance), and are not
considered ``subjective to the extreme,'' because of this exclusion.
Exclusion of igneous activity in the assessments for ground-water
protection and human intrusion is not expected to have a significant
effect on either assessment. The assessment for ground-water protection
is not affected because the dose from an igneous event is predominately
through the air pathway and not the ground-water pathway. The
assessment for human intrusion is not affected because the assumed
intrusion (i.e., single borehole to the water table) scenario leads to
a ground-water pathway, whereas the igneous event primarily involves
the air pathway. As the State has indicated, the air pathway is
considered in the assessment for individual protection.
Comment 2.4: The performance assessments for human intrusion and
individual protection should consider similar FEPs, to provide a
meaningful comparison of repository resilience.
Response 2.4: As discussed in the previous responses (under
Comments 2.2 and 2.3), each of the three performance assessments (i.e.,
those conducted to demonstrate compliance with the standards for
individual protection, ground-water protection, and resiliency to an
assumed human intrusion) has its own specific purpose, assumptions, and
standards. The EPA standards and NRC's regulations do not require that
direct comparisons be made between any of these assessments. The
performance assessment for human intrusion demonstrates the resilience
of the repository by assuming a specified intrusion occurs and by
requiring potential exposures to comply with the same overall exposure
limit [i.e., 0.15 mSv/yr (15 mrem/yr) from all pathways] used for
individual protection. Although the EPA standards clearly state
``unlikely'' FEPs are not to be included in the assessment for human
intrusion and ground-water protection (40 CFR 197.36), the performance
assessments for individual protection, ground-water protection, and
human intrusion provide a comprehensive evaluation of FEPs to inform
the licensing decision. Regardless of which aspect of repository
performance is the largest risk contributor, the regulatory
[[Page 62633]]
requirements for all assessments must be met.
Comment 2.5: The possibility of multiple intrusions into the
repository should be considered as a likely event and included in the
evaluation of human intrusion rather than the ``single'' intrusion
prescribed in the EPA standards and adopted in NRC's regulations.
Response 2.5: The State raised a similar concern (i.e.,
consideration for multiple intrusions) during the public comment period
for part 63. The Commission addressed this issue when it finalized part
63, stating:
Another related issue is whether the stylized calculation should
consider multiple intrusions. The final EPA standards resolve this
issue in favor of a single intrusion. Moreover, in its findings and
recommendations, NAS [National Academy of Sciences] argued against
analyses of whether and how often exploratory drilling would occur
at Yucca Mountain because of the complexities associated in such
assessments. Simply stated, the NAS felt that no one can accurately
predict the characteristics of future human society and their
technology. In the context of human intrusion, estimating the
probability of exploratory drilling for a given resource relies on
an ability to predict certain economic and technical factors that
influence supply of, and demand for, that resource. In fact, NAS
noted that the continued advances in noninvasive geophysical
techniques may, in fact, reduce the number and frequency of
exploratory boreholes * * *
Consequently, any consideration for the drilling of multiple
exploratory boreholes or later drilling of more boreholes further
increases the speculative nature of the intrusion scenario with
potentially little increase in understanding repository resilience.
The EPA standards provide for consideration of a single borehole at
the earliest time that human intrusion into the waste package can occur
without recognition by the drillers. The Commission believes this is an
appropriate test for evaluating repository resilience. Moreover, the
suggested alternative to evaluate multiple intrusions for the human
intrusion calculation fails to reflect the purpose of the human
intrusion calculation, that is to test the resilience of the
repository, not to evaluate the speculative issue of frequency of the
intrusion (66 FR 55761; November 2, 2001).
3. DOE Comments
DOE supports NRC's proposed probability range for defining unlikely
FEPs as a reasonable and conservative choice.
Comment 3.1: For assessing operational safety of the repository,
NRC's regulations specify that operational events that occur one or
more times during the operational period are considered reasonably
likely to occur. Applying this definition (i.e., one or more times) to
the specification of a value to define unlikely FEPs results in an
upper bound of one chance of occurrence within 10,000 years (i.e.,
approximately 10-4 annual probability). Thus, NRC's proposal
of an upper bound of one chance in ten of occurring within 10,000 years
(i.e., 10-5 annual probability) for unlikely FEPs is a
reasonable and conservative approach.
Response 3.1: During the development of the proposed rulemaking,
NRC considered an annual probability of 10-4 for the
demarcation between likely and unlikely FEPs, but ultimately decided on
a probability of one chance in ten of occurring within 10,000 years
(i.e., annual probability of 10-5) as a prudent value, given
the uncertainties in estimating the occurrence of FEPs over the very
long compliance period. The Commission was careful to point out that
its specification for unlikely events was in the context of very
specific assessments (i.e., those made to assess compliance with
ground-water protection and human-intrusion standards) over a long time
frame, and this specification was not intended to suggest or imply
precedent for other significantly different applications that used the
term ``unlikely'' (67 FR 3630; January 25, 2002). Similarly,
significantly different applications such as requirements for the
safety assessment of the operational period (e.g., significantly
shorter time period, inclusion of worker activities) should not imply a
precedent for specifying a value for unlikely FEPs.
4. NEI Comments
NEI supports NRC's proposed probability range for defining unlikely
FEPs. NEI stated that the proposed definition of unlikely FEPs will
facilitate a reasonable and prudently conservative analysis of these
aspects of repository performance (i.e., ground-water protection and
human intrusion).
5. Exelon Generation Comments
Exelon Generation supports NRC's proposed probability range for
defining unlikely FEPs.
III. Changes From the Proposed Rule
Section 63.342 Limits on Performance Assessments
The word ``should'' has been replaced with the word ``shall'' to be
consistent with the final EPA standard (40 CFR 197.36).
IV. Section-by-Section Analysis
Section 63.342 Limits on Performance Assessments
This section specifies how DOE will determine which features,
events, and processes will be considered in the performance assessments
described in subpart L of part 63.
V. 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
using such a standard is inconsistent with applicable law or is
otherwise impractical. In this rule, NRC is establishing probability
limits for unlikely FEPs at a potential geologic repository for high-
level radioactive waste at Yucca Mountain, Nevada. This action does not
constitute the establishment of a standard that contains generally
applicable requirements.
VI. Finding of No Significant Environmental Impact: Availability
Pursuant to section 121(c) of the Nuclear Waste Policy Act, this
rule does not require the preparation of an environmental impact
statement under section 102(2)(c) of the National Environmental Policy
Act of 1969 or any environmental review under subparagraph (E) or (F)
of section 102(2) of such act.
VII. Paperwork Reduction Act Statement
This 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 the Office of
Management and Budget (OMB), approval number 3150-0199.
Public Protection Notification
If a means used to impose an information collection requirement
does not display a currently valid OMB control number, NRC may not
conduct nor sponsor, and a person is not required to respond to, the
information collection.
VIII. 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. It is available for
inspection in the NRC Public Document Room, One White Flint North,
11555 Rockville Pike, Rockville, MD 20852.
[[Page 62634]]
Single copies of the analysis may be obtained from Clark Prichard,
Office of Nuclear Material Safety and Safeguards, U.S. Nuclear
Regulatory Commission, Washington, DC 20555-0001, telephone (301) 415-
6203, e-mail: nrc.gov">cwp@nrc.gov.
IX. Regulatory Flexibility Certification
In accordance with the Regulatory Flexibility Act [5 U.S.C.
605(b)], the Commission certifies that this rule will not, if
promulgated, have a significant economic impact on a substantial number
of small entities. This rule relates to 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
size standards established by the NRC (10 CFR 2.810).
X. Backfit Analysis
NRC has determined that the backfit rule does not apply to this
rule and, therefore, that a backfit analysis is not required, because
this rule does not involve any provisions that would impose backfits as
defined in 10 CFR chapter 1.
XI. Small Business Regulatory Enforcement Fairness Act
In accordance with the Small Business Regulatory Enforcement 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, Nuclear materials, Reporting and recordkeeping requirements,
Waste treatment and disposal.
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
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).
2. Section 63.342 is revised to read as follows:
Sec. 63.342 Limits on performance assessments.
DOE's performance assessments shall not include consideration of
very unlikely features, events, or processes, i.e., those that are
estimated to have less than one chance in 10,000 of occurring within
10,000 years of disposal. DOE's assessments for the human-intrusion and
ground-water protection standards shall not include consideration of
unlikely features, events, and processes, or sequences of events and
processes, i.e., those that are estimated to have less than one chance
in 10 and at least one chance in 10,000 of occurring within 10,000
years of disposal. 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 occurrence
if the results of the performance assessments would not be changed
significantly.
Dated at Rockville, Maryland, this 2nd day of October, 2002.
For the Nuclear Regulatory Commission.
Annette Vietti-Cook,
Secretary of the Commission.
[FR Doc. 02-25521 Filed 10-7-02; 8:45 am]
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