[Federal Register Volume 67, Number 17 (Friday, January 25, 2002)]
[Proposed Rules]
[Pages 3628-3631]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-1891]


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 Proposed Rules
                                                 Federal Register
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 This section of the FEDERAL REGISTER contains notices to the public of 
 the proposed issuance of rules and regulations. The purpose of these 
 notices is to give interested persons an opportunity to participate in 
 the rule making prior to the adoption of the final rules.
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  Federal Register / Vol. 67, No. 17 / Friday, January 25, 2002 / 
Proposed Rules  

[[Page 3628]]



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: Proposed rule.

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

SUMMARY: The Nuclear Regulatory Commission (NRC) is proposing to amend 
its regulations governing the disposal of high-level radioactive wastes 
in a potential geologic repository at Yucca Mountain, Nevada, to define 
the term ``unlikely'' in quantitative terms. That is, it would be 
defined as a range of numerical values for use in determining whether a 
feature, event, or process (FEP) or sequence of events and processes 
should be excluded from certain required assessments. The NRC is 
proposing this amendment to clarify how it plans to implement two of 
the final environmental standards for Yucca Mountain issued by the U.S. 
Environmental Protection Agency (EPA). Specifically, EPA's final 
standards require the exclusion of ``unlikely'' FEPs, 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, the NRC has adopted EPA's final standards in 
its recently published technical requirements for a potential geologic 
repository at Yucca Mountain.

DATES: The comment period expires April 10, 2002. Comments received 
after this date will be considered if it is practical to do so, but NRC 
is able to assure consideration only for comments received on or before 
this date.

ADDRESSES: Submit comments to: Secretary, U.S. Nuclear Regulatory 
Commission, Washington, DC 20555-0001, Attn: Rulemakings and 
Adjudications Staff.
    Deliver comments to 11555 Rockville Pike, Rockville, MD, between 
7:30 a.m. and 4:15 p.m. on Federal workdays.
    You may also provide comments via NRC's interactive rulemaking 
website http://ruleforum.llnl.gov. This site provides the capability to 
upload comments as files (any format) if your web browser supports that 
function. For information about the interactive rulemaking website, 
contact Ms. Carol Gallagher (301) 415-5905; e-mail nrc.gov">cag@nrc.gov.
    Certain documents related to this rulemaking, including comments 
received, may be examined at the NRC Public Document Room (PDR), Room 
O-1F23, 11555 Rockville Pike, Rockville, MD. These same documents may 
also be viewed and downloaded electronically via the rulemaking 
website.
    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/NRC/ADAMS/index.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 email 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), the U.S. Nuclear Regulatory 
Commission (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. 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, Public Law 102-486 
(EnPA), NRC's final rule adopts the radiation protection standards 
established by the U.S. Environmental Protection Agency (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 (FEPs) 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). DOE's performance 
assessments shall not include consideration of ``very unlikely'' 
features, events or processes (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 ``* * * considers a 
frequency for unlikely FEPs would fall somewhere between 10 
-8 to 10 -4 per year * * *,'' but that it had 
decided not to provide a specific quantitative value for defining 
unlikely FEPs in the final rule (66 FR 55734; November 2, 2001). 
Instead, the Commission stated that it ``* * *

[[Page 3629]]

plan[ned] to conduct an expedited rulemaking to quantitatively define 
the term ``unlikely.'' Consideration will be given to whether a range 
of values or a single specific value should be used as well as the 
appropriate numerical value(s). The expedited rulemaking will provide 
an opportunity for public comment to assist the Commission in 
determining an appropriate approach'' (66 FR 55734; November 2, 2001). 
This proposed rule initiates the rulemaking to quantitatively define 
the term ``unlikely'' promised by the Commission.

II. Discussion

    EPA's standards for disposal include an individual protection 
standard; a human intrusion standard; and ground-water protection 
standards. EPA's standards also prescribe that DOE should exclude 
``very unlikely'' FEPs from the performance assessments used to 
determine compliance with the three postclosure standards (i.e., 
individual protection, human intrusion, and ground-water protection). 
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 to the consequences of human intrusion. In the case of the 
performance assessment for ground-water protection, the purpose is to 
evaluate the degradation of the ground-water resource. Consistent with 
the specific purposes of these two standards, EPA prescribed specific 
conditions to be used in determining compliance with the human 
intrusion standard and the ground-water protection standards. For these 
two standards, EPA prescribed the exclusion of not only ``very 
unlikely'' FEPs, but also ``unlikely'' FEPs. 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\ This 
intent is consistent with the NRC approach of requiring the use of 
reasonable and prudently conservative assumptions in modeling exposure 
scenarios.
---------------------------------------------------------------------------

    \1\ For example, the preamble states: (1) ``[t]he assessment of 
resource pollution potential is based upon the engineered design of 
the repository being sufficiently robust under expected conditions 
to prevent unacceptable degradation of the ground-water resources 
over time'' (66 FR 32114; June 12, 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 intrustion 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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    Under 10 CFR 63.321(b)(1), DOE must demonstrate the earliest time 
after disposal that the waste package would degrade sufficiently that a 
human intrusion could occur without recognition by the drillers and ``* 
* * demonstrate that there is a reasonable expectation that the 
reasonably maximally exposed individual receives no more than an annual 
dose of 0.15 mSv (15 mrem) as a result of a human intrusion, at or 
before 10,000 years after disposal.'' The elements of the stylized 
human intrusion scenario are specified by 10 CFR 63.322 and 
specifically direct DOE to assume that no releases are included which 
are caused by unlikely natural processes and events. With respect to 
the ground-water standards (10 CFR 63.331), DOE must demonstrate that 
there is a reasonable expectation that, for 10,000 years of undisturbed 
performance (i.e., 10,000 years during which the occurrence of unlikely 
FEPs do not disturb the repository) after disposal, releases of 
radionuclides from waste in the Yucca Mountain disposal system into the 
accessible environment will not cause the level of radioactivity in the 
representative volume of ground water to exceed the limits specified in 
a table attached to 10 CFR 63.331.
    In assessing compliance with both the human intrusion standard and 
ground-water protection standards, 10 CFR 63.342 provides that unlikely 
FEPs, or sequences of events and processes, shall be excluded ``* * * 
upon prior Commission approval for the probability limit used for 
unlikely FEPs.'' Although the Commission could review and approve a 
probability limit in the context of its review of a potential DOE 
license application, it is proposing to set this limit in advance, 
through the rulemaking process, so that it will have the advantage of 
public views on this question, and so that DOE, interested 
participants, and the public will have knowledge, before the license 
application, of what probability the Commission would find acceptable.
    The Commission has considered whether the probability for unlikely 
FEPs should be defined as a single value or a range of values. A single 
value would be used as a probability limit such that each FEP with a 
probability less than the specified limit should be considered 
unlikely. A probability range would be used to define the spread of 
probability (i.e., upper and lower values) that represents unlikely 
FEPs. Although both approaches specify an upper value for probability, 
a probability range provides a more complete description of the spread 
of probability that is identified with unlikely FEPs. The Commission is 
not aware of any disadvantages to using a range and therefore is 
specifying a probability range because it provides a better 
characterization of the range of probabilities associated with FEPs 
than what would be provided by a single number.
    Assigning specific numerical values to a qualitative term such as 
``unlikely'' is complicated by the subjective nature of this term. As a 
first step, the Commission found it useful to describe three broad 
categories to represent the entire probability range for what could 
occur at the Yucca Mountain repository site. These three categories 
are: (1) Very unlikely; (2) unlikely; and (3) likely. As a practical 
matter, the rationale for the quantitative range defining unlikely FEPs 
is easier to describe in terms of the categories of likely and very 
unlikely, because unlikely is bounded by these two categories. Very 
unlikely FEPs have been described in the EPA standards as FEPs with 
such low probability of occurrence that they need not be considered in 
any performance assessments for Yucca Mountain. As mentioned 
previously, the EPA standards quantitatively define very unlikely FEPs 
as those FEPs with less than a 0.01 percent chance of occurring within 
the 10,000 year compliance period (i.e., annual probability less than 
10 -8). In a qualitative sense, likely FEPs are those FEPs 
that can be reasonably expected to occur during the 10,000 year 
compliance period. 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\ 
However, 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 believes a prudent decision is to consider FEPs with 10 
percent or greater chance of occurring within the 10,000 year 
compliance period as likely FEPs. Thus, unlikely FEPs are defined as 
those FEPs with less than a 10

[[Page 3630]]

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).
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    \2\ Estimating a high probability of occurrence for an FEP 
creates an expectation than an FEP will occur, however, it does not 
guarantee such an occurence; there is a chance that even high 
probability FEPs will not occur.
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    In light of the foregoing discussion, the Commission seeks comment 
on the appropriateness of using an annual probability range of greater 
than or equal to 10 -8 and less than 10 -5 to 
define unlikely FEPs. As a matter of reference, current understanding 
of FEPs relevant to Yucca Mountain indicates that this designation 
would allow exclusion of igneous activity as an unlikely FEP, whereas a 
wide range of seismic events, fault movement, and rock fall would have 
higher probabilities than the upper bound for unlikely FEPs and would 
be included in the performance assessments for human intrusion and 
ground-water protection.
    In arriving at this decision, the Commission considered the merits 
of using a lower value for the demarcation between likely and unlikely 
FEPs. For example, a 1 percent chance of occurring over the 10,000 year 
compliance period (i.e., annual probability of 10 -6) would 
also be considered unlikely. It is somewhat subjective whether a 
qualitative term such as ``unlikely'' should be quantitatively defined 
as less than a 1 or a 10 percent chance of occurring. Selection of an 
appropriate value needs to consider the context of the performance 
assessments (i.e., robustness of the repository system to the 
consequences of human intrusion and the degradation of the ground-water 
resource). As mentioned previously, the focus of the performance 
assessments for human intrusion and ground-water protection is to be on 
expected conditions. The Commission considers that an FEP having a 1 
percent chance of occurring is neither expected nor likely and, 
therefore, an inappropriate value for the lower bound for likely 
events. The Commission believes a lower bound for likely FEPs of a 10 
percent chance of occurring within the compliance period is consistent 
with the intended focus for these two standards. Although ``unlikely'' 
FEPs would not be considered in the performance assessments for human 
intrusion and ground-water protection, these FEPs are required to be 
considered in the performance assessment for the individual protection 
standard.
    This rulemaking is proposing a probability range for unlikely FEPs 
as part of NRC's implementation of EPA's final standards for Yucca 
Mountain, in accordance with EnPA. Specification of the probability for 
unlikely FEPs is in the context of assessments of compliance with the 
human intrusion standard and ground-water protection standards, which 
have a regulatory compliance period of 10,000 years. The Commission 
made clear in its final regulations in Part 63 that the ``[C]riteria 
set out in this final rule apply specifically and exclusively to the 
proposed repository at Yucca Mountain'' (66 FR 55732; November 2, 
2001). Similarly, the proposed definition for the term ``unlikely'' in 
this rulemaking is intended to apply specifically and exclusively to 
the potential repository at Yucca Mountain and is not intended to 
suggest or imply precedent for NRC regulations in other parts of this 
Chapter that use the term ``unlikely'' in significantly different 
contexts (e.g., compliance periods of tens of years, higher dose 
limits, different facilities, and different activities).

III. 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.

IV. Plain Language

    The Presidential memorandum dated June 1, 1998, entitled ``Plain 
Language in Government Writing'' directed that the Government's writing 
be in plain language. This memorandum was published on June 10, 1998 
(63 FR 31883). The NRC requests comments on the proposed rule 
specifically with respect to the clarity and effectiveness of the 
language used. Comments should be sent to the address listed under the 
ADDRESSES caption of the preamble.

V. Voluntary Consensus Standards

    The National Technology Transfer and Advancement Act of 1995, 
Public Law 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 proposed rule, the 
NRC is establishing probability limits for unlikely features, events, 
and processes 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 
proposed 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 proposed 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, approval number 3150-0199.

Public Protection Notification

    If a means used to impose an information collection does not 
display a currently valid OMB control number, the NRC may not conduct 
or sponsor, and a person is not required to respond to, the information 
collection.

VIII. Regulatory Analysis

    The Commission has prepared a draft regulatory analysis on this 
proposed regulation. The analysis examines the costs and benefits of 
the alternatives considered by the Commission. The Commission requests 
public comment on the draft regulatory analysis. Comments on the draft 
analysis may be submitted to the NRC as indicated under the ADDRESSES 
heading. It is available for inspection in the NRC Public Document 
Room, One White Flint North, 11555 Rockville Pike, Rockville, MD 20852. 
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 proposed rule will not, if 
promulgated, have a significant economic impact on a substantial number 
of small entities. This proposed 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.

X. Backfit Analysis

    NRC has determined that the backfit rule does not apply to this 
proposed

[[Page 3631]]

rule and, therefore, that a backfit analysis is not required, because 
this proposed rule does not involve any provisions that would impose 
backfits as defined in 10 CFR Chapter 1.

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. 553, NRC is proposing to adopt the following 
amendments to 10 CFR Part 63.

PART 63--DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTE 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 should 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 should 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 18th day of January, 2002.

    For the Nuclear Regulatory Commission.
Annette Vietti-Cook,
Secretary of the Commission.
[FR Doc. 02-1891 Filed 1-24-02; 8:45 am]
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