Review Methodology for Seismically Initiated Event Sequences; Availability of Final Interim Staff Guidance Document, 57579-57584 [E6-16017]
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Please specify the report number
NUREG–0800, Section 13.3, Second
Draft Revision 3, in your comments, and
send your comments by November 13,
2006.
FOR FURTHER INFORMATION, CONTACT:
Bruce Musico, Mail Stop O–6H2, U.S.
Nuclear Regulatory Commission,
Washington, DC 20555–0001.
Telephone: (301) 415–2310; internet:
bjm2@nrc.gov.
SUPPLEMENTARY INFORMATION: This
Standard Review Plan, NUREG–0800,
has been prepared to establish criteria
that the NRR and NSIR staff responsible
for the review of applications to
construct and operate nuclear power
plants intends to use in evaluating
whether an applicant/licensee meets the
NRC’s regulations. The Standard Review
Plan is not a substitute for the NRC’s
regulations, and compliance with it is
not required. However, applicants are
required to identify differences in
design features, analytical techniques,
and procedural measures proposed for a
facility and corresponding SRP
acceptance criteria, and evaluate how
the proposed alternatives to the SRP
acceptance criteria provide an
acceptable method of complying with
the NRC’s regulations.
The standard review plan sections are
keyed to Regulatory Guide 1.70,
‘‘Standard Format and Content of Safety
Analysis Reports for Nuclear Power
Plants (LWR Edition).’’ Not all sections
of the standard format have a
corresponding review plan section. For
combined license applications
submitted under 10 CFR part 52, the
applicability of standard review plan
sections will be based on the Regulatory
Guide DG–1145, ‘‘Combined License
Applications for Nuclear Power Plants
(LWR Edition),’’ as superceded by the
final guide.
The proposed revision is a rewrite of
the July 1981 SRP Section 13.3,
Revision 2, and provides staff guidance
for the review of emergency planning
information submitted in license
applications under 10 CFR parts 50 and
52. In addition to updating the July 1981
SRP section, the proposed revision
includes some of the proposed changes
in the April 1996 draft Revision 3 to
SRP section 13.3. The proposed revision
consists mostly of changes that identify
specific regulations and guidance, and
provides SRP acceptance criteria for the
various applications submitted under
both 10 CFR parts 50 and 52. The most
significant changes reflect the new
application processes allowed by 10
CFR part 52. This also includes the
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incorporation of Commission policy on
the use of emergency planning
inspections, tests, analyses, and
acceptance criteria (EP–ITAAC), which
is addressed in the February 22, 2006,
SRM SECY–05–0197, ‘‘Review of
Operational Programs in a Combined
License Application and Generic
Emergency Planning Inspections, Tests,
Analyses, and Acceptance Criteria’’
(ML052770225). In addition, the
proposed revision incorporates
experience gained from the first three
early site permit (ESP) application
reviews, and the standard design
certification applications. The license
application review processes in both 10
CFR part 50 and part 52 utilize the same
existing emergency planning
requirements contained primarily in 10
CFR 50.47 and Appendix E to part 50.
While the proposed SRP Section 13.3
revision is a complete rewrite of Section
13.3, it does not contain new or
unreviewed staff positions. It does,
however, identify a new NUREG/CR
report on evacuation time estimates
(ETEs). Guidance on the development of
ETEs was provided in November 1980
in NUREG–0654/FEMA–REP–1,
Revision 1, ‘‘Criteria for Preparation and
Evaluation of Radiological Emergency
Response Plans and Preparedness in
Support of Nuclear Power Plants,’’ and
that guidance is still used today. The
staff will continue to use the established
guidance and criteria in Appendix 4,
‘‘Evacuation Time Estimates Within the
Plume Exposure Pathway Emergency
Planning Zone,’’ of NUREG–0654/
FEMA–REP–1, as the basis for
compliance with applicable regulations.
The new (January 2005) ETE report,
NUREG/CR–6863, ‘‘Development of
Evacuation Time Estimate Studies for
Nuclear Power Plants,’’ is identified in
the proposed SRP Section 13.3 revision
as providing information relating to
performing an ETE analysis. In March
1992, NUREG/CR–4831, ‘‘State of the
Art in Evacuation Time Estimate
Studies for Nuclear Power Plants,’’ was
written to provide updated information,
assumptions, and methods to be used in
performing ETE studies. NUREG/CR–
6863 updates NUREG/CR–4831 and
integrates new technologies in traffic
management, computer modeling, and
communication systems to identify
additional tools useful in the
development of new, or updates to
existing, ETEs.
Of note, the proposed revision does
introduce the option to use EP–ITAAC
in an ESP application, which is
consistent with the ongoing 10 CFR part
52 rulemaking (see proposed 10 CFR
52.17(b)(3)). Prior to the current 10 CFR
part 52 rulemaking, the rules only
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addressed the use of EP–ITAAC with a
combined license (COL) application but
not at the ESP stage. The staff’s position,
which is supported by public
comments, is that the extension of EP–
ITAAC to ESP applications is not
precluded in the existing rules, and is
necessary in order to accommodate an
applicant’s submission of a ‘‘complete
and integrated emergency plan’’ at the
ESP stage, as well as provide an
additional level of flexibility for an ESP
applicant. Without allowing the use of
EP–ITAAC (or other such placeholders)
at the ESP stage, the staff would be
unable to reach a reasonable assurance
finding at the time of application. The
use of EP–ITAAC would allow the staff
to make its findings based on proposed,
and not yet implemented, emergency
plans. Table 13.3–1 provides a proposed
set of allowable EP–ITAAC (for use at
either the ESP or COL application
stage). The asterisked/bolded text in the
table represents the earlier set of COL
EP–ITAAC that was approved by the
Commission in SRM SECY–05–0197.
Table 13.3–1 reflects a process of review
allowed by 10 CFR part 52, and does not
contain new or unreviewed staff
positions relating to emergency
planning requirements.
Dated at Rockville, Maryland, this 25th day
of September, 2006.
For the Nuclear Regulatory Commission.
Robert Tregoning,
Branch Chief, New Reactor Infrastructure
Guidance, Development Branch, Division of
New Reactor Licensing.
[FR Doc. E6–16013 Filed 9–28–06; 8:45 am]
BILLING CODE 7590–01–P
NUCLEAR REGULATORY
COMMISSION
[HLWRS–ISG–01]
Review Methodology for Seismically
Initiated Event Sequences; Availability
of Final Interim Staff Guidance
Document
Nuclear Regulatory
Commission.
ACTION: Notice of availability.
AGENCY:
SUMMARY: The Nuclear Regulatory
Commission (NRC) is announcing the
availability of final interim staff
guidance (ISG) document, ‘‘HLWRS–
ISG–01, Review Methodology for
Seismically Initiated Event Sequences,’’
and NRC responses to the public
comments received on that document.
The ISG clarifies or refines the guidance
provided in the Yucca Mountain Review
Plan (YMRP) (NUREG–1804, Revision 2,
July 2003). The YMRP provides
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guidance to NRC staff for evaluating a
potential license application to receive
and possess high-level radioactive waste
at a geologic repository constructed or
operated at Yucca Mountain, Nevada.
ADDRESSES: The document HLWRS–
ISG–01 is available electronically at
NRC’s Electronic Reading Room, at
https://www.nrc.gov/reading-rm/
adams.html. From this site, you can
access NRC’s Agencywide Documents
Access and Management System
(ADAMS), which provides text and
image files of NRC’s public documents.
The ADAMS accession number for the
ISG is ML062650140. 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 1–800–397–4209, or (301) 415–
4737, or (by e-mail), at pdr@nrc.gov.
This document may also be viewed
electronically on the public computers
located at NRC’s PDR, Mail Stop:
O1F21, One White Flint North, 11555
Rockville Pike, Rockville, MD 20852.
The PDR reproduction contractor will
copy documents, for a fee.
NRC RESPONSES TO PUBLIC
COMMENTS ON HLWRS–ISG–1: In
preparing final HLWRS–ISG–01,
‘‘Review Methodology for Seismically
Initiated Event Sequences,’’ ADAMS
ML062650140, the NRC staff reviewed
and considered 23 comments received
from five different organizations during
the public comment period. One
commenter had 12 comments
recommending specific clarifying
changes to the ISG. One commenter
questioned NRC using the ISG to clarify
its regulatory intent, instead of
addressing the issue of seismically
initiated event sequences, more
appropriately, in the YMRP. Two
commenters questioned whether the ISG
sets forth a more stringent standard for
the seismic design of repository surface
facilities than the existing criteria for
reactors. One commenter was concerned
that a specific methodology described in
the ISG would bias the NRC staff’s
review against other methodologies that
the U. S. Department of Energy (DOE)
may propose that provide equal or better
protection of public health and safety.
One commenter was concerned that the
specific methodology proposed in the
ISG lacks both precedent and scientific
support. Two commenters were
concerned that the ISG methodology
may not produce accurate results over
the 100-year plus operating life of the
Yucca Mountain repository preclosure
operating period. Two commenters
raised questions as to whether NRC has
adequately considered the geometric
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consequence of closely spaced,
recurring seismic events, in determining
the seismic hazard and related failure
probability of a structure, system, or
component (SSC) important to safety
(ITS). One commenter states that ‘‘the
ISG totally ignores the existence of
Section 63.102(f) of the regulation.’’ The
following discussion indicates how the
comments were addressed, and the
changes, if any, made to the ISG as a
result of the comments.
Line numbers in the following
comments refer to the draft HLWRS–
ISG–01, ADAMS ML061170532, which
was made available for public comment
on May 22, 2006 (71 FR 29369).
1. Comment. The commenter
recommends that the sentence starting
at Line 38 be re-phrased as: ‘‘The mean
fragility curve for an SSC ITS may be
estimated using: (1) Probability density
functions for controlling parameters in a
Monte Carlo analysis; (2) simplified
methods outlined in Section 4 of
Electric Power Research Institute, TR–
103959 (Ref. 2); (3) a method that uses
the Conservative Deterministic Failure
Margin methodology to determine the
1percent probability of failure, and an
estimate of the composite logarithmic
standard deviation, as described by
Kennedy (2001, pp. 44 to 45) and
Ravindra (2006, p. 132); or (4) other
methods that capture appropriate
variability and uncertainty in
parameters used to estimate the capacity
of the SSCs ITS to seismic events.
Response. NRC regulations grant DOE
broad flexibility in choosing a method
or methods for preclosure safety
analysis of hazards at the geologic
repository operations area (GROA).
Although NRC staff has stated some
example methods, in the ISG, for
estimating the fragility curve, this does
not imply that alternative methods
would be unacceptable for
demonstrating compliance with
regulatory requirements. DOE may use
an alternative method, if sufficient
technical basis for the use of the method
is provided.
No changes were made to the ISG as
a result of this comment.
2. Comment. The commenter
recommends that the following sentence
be added at the end of the sentence on
line 43:
‘‘Where appropriate, assessment of fragility
for an SSC may be based on fragility values
for an identical or similar component as
found in the literature.’’
Response. NRC agrees with the
commenter that the fragility data for an
SSC, developed and documented in
databases and used at other facilities,
may be used to estimate fragility for the
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SSCs at the repository, if the data are
shown to be applicable to the repository
SSCs.
The ISG has been revised to add the
following at the end of the sentence on
Line 43:
‘‘An estimate of fragility for an SSC may be
based on fragility values for an identical or
similar component as found in the literature,
provided technical bases for the relevance of
the data to the SSC under consideration are
established.’’
3. Comment. The commenter
recommends that an explanation be
provided to address why the selection of
the slope (Lines: 235 to 237, 240 to 241:
Page: 8) is appropriate. This explanation
may include, for example, that this
portion of the hazard curve was selected
if it were the interval where the
dominant contribution to risk arises.
Text could be added at the end of the
sentence on Line 241:
‘‘The slope should be selected to focus on
the portion of the curve where risk is
expected to dominate the convolution.’’
Response. NRC agrees with the
commenter that an explanation for the
selection of the slope between
probabilities of exceedance of 10¥6 and
10¥5 should be added in the ISG.
The ISG has been revised to add the
following at the end of the sentence on
Line 241:
‘‘This slope was selected to represent the
hazard accurately at probabilities of
exceedance values close to the target annual
threshold probability of 10¥6 because this
portion of the hazard curve may have a
significant contribution to the risk.’’
4. Comment. The commenter suggests
replacing the sentence starting on Line
263, with the sentence: ‘‘For the
purposes of illustration, a single
response frequency of 10 hertz (Hz) is
assumed for this evaluation.’’ The
commenter also suggests that an
explanation of why a single frequency is
appropriate should be added.
Response. NRC believes that the
essence of the comment, with the
suggested change to the ISG, is
adequately responded to by the
sentences in lines 262 to 264 of the ISG.
These sentences state that the
evaluation typically would be
performed at appropriate structural
frequencies, based on the dynamic
characteristics of the SSC, and that
example evaluation is performed at a
single frequency of 10 hertz. A single
frequency was chosen in the example
for illustration purposes only. As stated
in the sentence in line 261, the
evaluation typically would have to be
performed for a number of structural
frequencies of an SSC, based on its
dynamic characteristics, to
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appropriately assess the probability of
failure of an SSC during a seismic event.
No changes were made to the ISG as
a result of this comment.
5. Comment. The commenter suggests
that text be added to include discussion
of other non-seismic factors that may
influence/mitigate the probability of
occurrence of the event sequence. At
line 262, a sentence should be inserted
to read:
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‘‘Other non-seismic factors such as
residency times, targeting factors, operational
states, and design constraints, which may
also influence the probability of occurrence
of the complete event sequence, are not
considered in this example.’’
Response. NRC agrees with the
commenter that in the example, design
constraints, such as the probability of
failure of the canister during a potential
drop event, are not considered. This is
indicated in Lines 276 to 277 of the ISG,
and in the clarifying statement added in
the ISG in response to comment 10.
NRC believes that the clarifying
statement recognizes that if the canister
breach probability (given a drop) is
demonstrated to be less than 1.0, the
appropriate conditional probability of
breach may be factored into the
quantification of the event sequence.
Therefore, NRC believes that a change to
the ISG to clarify this factor in
determining the probability of
occurrence of the event sequences is not
necessary. Other non-seismic factors
mentioned in the comment appear to be
related to the duration of operations at
the proposed Yucca Mountain
repository. NRC would need specific
information on the Yucca Mountain
repository operations and the technical
bases for determining the values of these
factors, to judge whether these factors
are appropriate and can be used to
calculate event sequence probability of
occurrence in the preclosure safety
analysis. NRC will review the use of
these factors and their technical bases
and make a determination of their
acceptability during the potential future
review of the DOE License Application
for the proposed Yucca Mountain
repository.
No changes were made to the ISG as
a result of this comment.
6. Comment. The commenter
recommends that the assumption made
in the computation be clarified, and that
each branch in the sequence be
addressed in the description (Lines: 308
to 323: Page: 12). For instance, at the
end of the sentence ending on Line 310,
the text should be expanded to mention
the other branches:
‘‘Tracing Sequence 3 across the event tree
shown in Figure B–1, this sequence also
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includes the STR–SHWL success branch and
the assumed failure of the canister (CANIS–
BRCH) * * *’’ Additional text on Lines 310
to 323 should include: ‘‘* * * the STR–
SHWL success probability is the complement
of the fragility of the failure branch * * *’’
and ‘‘* * * Therefore, the combined fragility
of the three systems in the event sequence
can be obtained by * * *.’’
Response. NRC agrees with the
commenter that the Event Sequence 3,
as shown in Figure B–1, implies that the
concrete shear wall provides a
confinement barrier to the release of
radioactive materials before they pass
through the Heating, Ventilation and
Air-Conditioning (HVAC) system.
However, for illustration purposes only,
it was assumed in the example that, if
the HVAC duct anchor system fails, all
radioactive materials released because
of the canister breach would be
discharged through the HVAC system.
To clarify this assumption, the ISG has
been revised as follows:
Add the following at the end of the
sentence in Line 309:
‘‘For simplicity, it is assumed, in this
example, that if the HVAC duct anchor
system were to fail, all radioactive materials
released because of the potential canister
breach would be discharged through the
HVAC system, and that the concrete shear
wall would be unable to provide a barrier to
the release of radioactive materials.’’
7. Comment. The commenter suggests
that Figure B–1 be revised for clarity,
making the figure consistent with
conventions for the construction of
event trees in other NRC documents,
such as NUREG–2300. The following
changes are suggested to Figure B–1:
(a) The figure be revised to indicate that
the initiating event of the sequence is an
earthquake;
(b) The figure heading be revised to state
the event in terms of success;
(c) The missing branch be shown for the
event that the crane does not drop the waste
form.
(d) The probability of canister breach,
which has been assumed to be 1.0, be
indicated.
Response. NRC agrees with the
suggested change in item (b), above,
regarding revision of the figure headings
and stating the event in terms of
success, and has revised Figure B–1.
Staff, however, does not agree with the
other suggested changes because the
title of the figure identifies the event
sequence as initiated by a seismic event.
This is also consistent with Section
11.2.6.2 of NUREG–2300. In addition,
adding a success path for the crane not
dropping the waste form would be
superfluous to this example, and would
not add any value to the illustration of
the procedure for event sequence
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probability calculation. The probability
of canister breach assumed as 1.0 is
stated in section B of Appendix B.
Figure B–1 has been revised as a
result of this comment.
8. Comment. Assuming that the text
in lines 220 to 222 has broader
applicability than just as part of the
example, the commenter suggests that
the sentence starting on Line 220 be
deleted from Appendix A, moved to the
Discussion section on page 1, and
inserted into the text at Lines 54 to 63.
The commenter also suggests changes to
the text for insertion into the Discussion
section on page 1, in comment 9.
Response. NRC agrees with the
comment. The ISG has been revised as
follows:
(a) The sentence starting on Line 220 and
ending on Line 222, ‘‘The technical basis
* * * staff review.’’, has been deleted.
(b) The following has been added at
the end of the sentence on Line 57:
‘‘Technical bases for the development of
the SSC ITS fragility curves should be
available for staff review.’’
9. Comment. The commenter suggests
that, the following sentence consistent
with the Comment 8, should be inserted
into the Discussion section on page 1 at
Lines 54 to 63:
‘‘It is necessary in developing seismic
fragilities that the technical basis for the
development of the applicable fragility
parameters be available for staff review.’’
Response. NRC agrees with the
essence of the comment. The ISG has
been revised as shown in NRC staff
response to comment 8, item (b).
10. Comment. The commenter
recommends adding the following
phrase to the end of Line 277:
‘‘* * * and it is assumed that probability
of breach is 1.0 in all cases’’. In addition, the
commenter recommends adding, in Figure B–
1, ‘‘(Pf = 1.0),’’ on the branch indicating
potential for breach. The commenter also
recommends adding text to state that when
the probability of a breach (given a drop) is
demonstrated to be less than 1.0, the
appropriate conditional probability of breach
may be factored into the quantification of the
event sequence.
Response. NRC agrees with the
comment. The ISG has been revised to
clarify that, for the example in
Appendix B, it is assumed that the
canister probability of failure (given a
drop) is 1.0. The comment regarding the
use of appropriate conditional
probability of canister failure, in the
event sequence probability calculation,
has been addressed in response to
comment 5.
The ISG has been revised to add the
following at the end of the sentence in
Line 277:
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‘‘It is assumed that the canister probability
of failure, given a drop, is 1.0.’’
11. Comment. The commenter
suggests adding the following text in the
sentence starting on Line 36:
‘‘As a conservative assessment of
probability, the probability of occurrence of
an event sequence leading to an SSC ITS
failure, or seismic performance, can be
determined by * * *’’
Response. NRC agrees with the
essence of the comment, and has added
a new sentence to reflect the comment.
The ISG has been revised to add the
following sentence in Line 36:
‘‘As a conservative assessment of the
probability of occurrence of an event
sequence, a single SSC ITS may be
considered, instead of all SSCs ITS in the
event sequence.’’
12. Comment. The commenter
suggests that a brief statement be added
at the end of line 232 and in Appendix
B, as follows:
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‘‘Computations shown in the appendix can
be performed either by hand computations or
through the use of computer codes. A
number of computer codes are available that
can be used for probability computations.’’
Response. NRC agrees with the
commenter that computations for the
event sequence probabilities can be
performed either by hand computations
or through the use of computer codes.
However, these options are available to
the applicant for any calculations.
Although the details of associated
quality assurance requirements may be
different for the computational method
selected, the overall staff review strategy
for the DOE analysis is not affected
significantly by the computational
method selected by DOE. Therefore,
staff does not see the need to revise the
ISG.
No changes were made to the ISG as
a result of this comment.
13. Comment. The commenter refers
to NRC Chairman Dale E. Klein’s
statement, on July 1, 2006, that
regulatory stability is a crucial element
in ensuring that NRC can complete its
work in a timely manner, and states that
HLWRS ISG–01 has the potential to
create regulatory instability.
Accordingly, the commenter encourages
NRC to take advantage of the
opportunity afforded by this comment
period to reconsider issuing this ISG
and to instead address the issue of
seismically initiated event sequences,
more appropriately, in the YMRP. The
commenter is recommending this course
of action for the following five reasons:
(a) ISG is not the most effective means
for NRC to clarify its regulatory intent
and could lead to unforeseen
consequences due to inadequate review
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(including not being reviewed by the
Commission itself).
(b) Use of an ‘‘Interim Guidance,’’ a
vehicle that was meant to address
emerging issues affecting multiple
licensed activities, is unnecessary in a
situation where there is only a single
potential licensee that is not currently
conducting any licensed activities.
(c) Draft HLRWS ISG–01 lacks safety
focus in that it sets forth a more
stringent standard for the seismic design
of repository surface facilities than
currently exists for reactors, without
recognizing the comparatively lower
level of risk associated with the
repository facilities. In doing this,
HLRWS ISG–01 directly contradicts the
very regulation (10 CFR Part 63) that it
seeks to inform.
(d) Providing guidance to staff that
assumes a specific methodology for
demonstrating compliance with 10 CFR
63.111 is likely to bias the staff’s review
against other methodologies, that DOE
may propose, which provide equal or
better protection of public health and
safety. Furthermore, giving DOE the
opportunity to first propose an
acceptable method for meeting the
regulation would allow for a more
independent NRC review—avoiding a
situation where NRC is both telling DOE
how to demonstrate compliance and
then determining if compliance was
demonstrated as instructed.
(e) The specific methodology
proposed in this draft ISG lacks both
precedent and scientific support.
Response. Responses to each of the
commenter’s reasons are provided
below:
(a) In the commenter’s view, the ISG
is not an effective means for NRC to
clarify its regulatory intent and could
lead to unforeseen consequences
because of inadequate review (including
not being reviewed by the Commission
itself).
The ISG reflects a focused revision of
the YMRP, with the scope of the
revision limited to a specific technical
issue. The ISG process allows for the
rapid identification and resolution of
specific technical issues that emerge as
a result of staff interaction, with DOE,
in preparation for the future License
Application review. To increase
regulatory efficiency and enhance
clarity of communication with DOE and
the public, NRC anticipates providing
incremental updates to the YMRP in the
form of ISGs. NRC believes it is
unnecessary and inefficient to republish
the YMRP, given the narrow scope of
the technical issue addressed in the ISG.
If re-publication of the YMRP is
warranted (e.g., due to a major rule
change or accumulation of a number of
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ISGs), staff will be able to insert the
appropriate text directly from the ISG
into the YMRP. The ISG remains
available to provide background
discussion and examples, to supplement
text, in the YMRP, at a level of detail not
normally found in a Standard Review
Plan (SRP). Thus, staff sees the ISG
process as an effective, efficient, and
appropriate means for revising or
supplementing the YMRP.
An ISG provides guidance to NRC
staff on approaches to use during the
review of a potential license
application. ISG guidance is for
illustration purposes only, and does not
imply a preferred method or an
approach that an applicant must use. An
ISG’s review approach provides a
framework for staff to conduct an
efficient review, consistent with
regulatory requirements. ISGs, that are
revisions or supplements to the SRPs,
are issued at the NRC Office Division
level, because SRPs do not represent
regulatory commitments, or staff
interpretations. During the ISG
development process, the technical and
regulatory basis for the ISG is
thoroughly reviewed by appropriate
NRC technical, management, and legal
staff. Also, the public and shareholders
are informed of a proposed draft ISG
and afforded the opportunity to
comment. Comments from the public
and stakeholders are considered in
developing the final ISG.
No changes were made to the ISG as
a result of this comment.
(b) In the commenter’s view, ISGs are
not necessary for the Yucca Mountain
project because DOE is the only
potential licensee for the proposed
repository, and no licensing activities
are being conducted currently. Although
it is true that DOE is the only potential
licensee and no licensing activities are
currently underway, important
technical issues continue to be
identified in the complex, one-of-a-kind
Yucca Mountain project during the
prelicensing interaction with DOE. As
these issues are being resolved, the ISG
process provides an effective, efficient,
and appropriate means for staff to revise
or supplement the YMRP, as discussed
in response to comment 13(a). The ISG
process also allows staff to
communicate with potential licensees
on the scope of the staff reviews on
specific technical issues, as NRC staff
prepares to review the potential License
Application in an effective and timely
manner.
No changes were made to the ISG as
a result of this comment.
(c) In the commenter’s view, ISG–01
lacks safety focus and sets forth a more
stringent standard for the seismic design
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of repository surface facilities than for
reactors even though the repository
facility has a lower level of risk, which
appears contradictory to the intent of 10
CFR Part 63. The commenter also
questions the purpose of 10 CFR
63.102(f) and how it is accounted for in
the draft HLWRS–ISG–01. Another
commenter made a similar statement.
NRC does not agree with the
commenter that the ISG–01 proposed
methodology for seismically initiated
event sequences sets forth a more
stringent standard for the seismic design
of repository facilities than for reactors.
NRC also does not agree that the ISG–
01 contradicts the intent of Part 63. The
methods discussed in the draft ISG do
not mandate seismic design
requirements, but present approaches
that NRC staff could use to review the
performance of SSCs ITS for seismically
initiated event sequences, as required in
Part 63.
The preclosure compliance
requirements in Part 63 are
performance-based, in that instead of
specifying specific design loads and
corresponding acceptance criteria (i.e.,
codes/standards) the regulations in 10
CFR 63.111, for the GROA, specify
radiological dose limits to the public
and workers. In the preclosure safety
analysis (PCSA), DOE must demonstrate
that the GROA design will meet these
dose limits, taking into consideration
credible event sequences.
The ISG–01 provides a methodology
to determine if a seismically initiated
event sequence is a Category 2 event
sequence, as defined in 10 CFR 63.2, or
if it is beyond Category 2 and can be
screened out from further consideration.
If the event sequence is determined to
be a Category 2 event sequence, DOE
has to demonstrate that the dose limit of
5 roentgen equivalent man (rem) at any
point on the boundary of the site is met.
These performance-based requirements
in Part 63 necessarily result in a
different type of compliance
demonstration than is traditionally used
for reactor licensing.
For reactors, a seismic event is
directly related to the characteristics of
a specified safe shutdown earthquake
(10 CFR Part 50, Appendix S), which is
used as the design basis for each of the
safety-related SSCs, and demonstration
of compliance with regulations. In
contrast, Part 63 does not specify
seismic or other design bases or SSCs,
but instead requires consideration of
credible event sequences and their
potential consequences. The guidance
in the draft ISG shows how the
fragilities of one or more SSCs in an
event sequence can be combined with
the seismic hazard curve to determine
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the likelihood of an entire event
sequence, which is the metric used for
compliance in Part 63. Section 63.102(f),
which allows initiating events to be
considered based on precedents adopted
for nuclear facilities with comparable or
higher risks, was not used in the ISG–
01 because the compliance
demonstration for Part 63 requires safe
performance of SSCs in seismically
initiated event sequences, instead of a
single initiating seismic event (i.e., safeshutdown earthquake) that is
traditionally used as a design basis in
reactor licensing.
DOE will need to design to a level of
performance sufficient to meet the
requirements of Part 63, for seismically
initiated event sequences. DOE is given
broad flexibility in selecting a preferred
design basis, and determining the
degree of defense-in-depth contained
within the GROA system. Although
DOE must provide the basis for its
proposed designs, compliance with Part
63 will be determined by the
performance of the design during
credible seismically initiated event
sequences, not by adherence to a
predetermined design basis for a seismic
event.
No changes were made to the ISG as
a result of this comment.
(d) In the commenter’s view, the
specific methodology in the ISG–01 may
bias the staff’s review against other
methodologies that DOE may propose,
even if these alternatives provide equal
or better protection of public health and
safety. The commenter also raises the
concern that NRC should not dictate to
DOE how to demonstrate compliance
with regulations because it does not
allow for a more independent review of
the future DOE License Application.
NRC does not agree with the comment
that providing a methodology for
seismically initiated event sequences in
ISG–01 may preclude DOE from
proposing other methodologies for
complying with Part 63. Similar to the
YMRP, ISGs are prepared to provide
guidance to the staff for review of any
future License Application, from DOE,
for the proposed Yucca Mountain
repository, and are not mandatory. DOE
has the option of proposing alternative
methodologies to comply with the
regulations, which the staff would
evaluate during its review of the License
Application. As discussed in response
to Comment 1, presenting an example
methodology in an ISG does not imply
a preference for that method in
licensing, and does not restrict the
ability of an applicant to use an
alternative method.
No changes were made to the ISG as
a result of this comment.
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57583
(e) In the commenter’s view, the
specific methodology proposed in the
draft ISG–01 lacks both precedent and
scientific support. The commenter
raises the concern that applying
technical analysis to seismic events
with probability of exceedance lower
than one in 10,000 per year to establish
design bases is unprecedented, and that
it would result in stringent design
criteria. Staff disagrees with the
commenter’s concern because ISG–01
does not provide guidelines on the
design bases or design criteria for the
SSCs, of the GROA, at the repository,
but provides one method for NRC staff
to use in reviewing demonstration of
compliance with the performance
requirements for the SSCs in the PCSA.
Additionally, the methodology
proposed in the draft ISG has precedent
in the mixed-oxide fuel fabrication
facility at the Savannah River Site in
South Carolina, where the applicant
used a methodology similar to the one
outlined in the draft ISG to demonstrate
performance of the facility during
seismic event sequences.
NRC disagrees with the comment that
the methodology proposed in ISG–01
lacks scientific support. The proposed
ISG–01 methodology to evaluate seismic
performance of an SSC ITS is consistent
with the performance-based
methodology in the consensus standard
ASCE 43–05. The methodology has the
scientific support of the experts in the
industry, and is not beyond the state-ofthe-art for performance evaluation of
SSCs for seismic hazard.
No changes were made to the ISG as
a result of this comment.
14. Comment. Two commenters stated
that NRC’s decision to approve the use
of the methodology that is similar to the
one outlined in ASCE 43–05 appeared
to be based on the method’s recent use
in licensing of the mixed-oxide fuel
fabrication facility at the Savannah
River Site. The MOX facility has a
projected operating life of 20–40 years
and it is assumed that the NRC
operating license is for the same period
of time. The commenters are concerned
about the ability of ASCE 43–05 to
appropriately account for uncertainty
over the longer time-frame for Yucca
Mountain, given that the preclosure
operating period for the repository
project could be 100 years or longer.
The commenter adds that NRC should
address this issue in the final staff
guidance.
Response. The commenters raise a
concern that the ISG–01 methodology,
as suggested by ASCE 43–05, may not
produce accurate results over a potential
100-year or longer operating life of the
Yucca Mountain repository preclosure
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operating period. The preclosure
operating period of the Yucca Mountain
repository may affect the ISG–01
methodology results in two ways: (i) In
categorization of seismically initiated
event sequences (e.g., one chance in
10,000 of occurrence during the
preclosure period specified in Part 63
for category 2 event sequences); and (ii)
in development of the SSCs ITS seismic
fragility curves, with potential changes
in material properties resulting from
degradation during the preclosure
period. Staff believes that the
uncertainties, considered in the seismic
hazard and SSCs ITS fragility curves
development, would sufficiently
account for potential materials
degradation during the preclosure
period.
No changes were made to the ISG as
a result of this comment.
15. Comment. Two commenters stated
that the example provided in Appendix
A raises questions as to whether NRC
has adequately considered the geometric
consequence of closely spaced,
recurring, seismic events in determining
the mean seismic hazard and related
failure probability of an SSC ITS.
HLWRS–ISG–01 and/or the YMRP may
need to be revised to ensure that such
characteristics of seismic hazard and
related failure probability are
appropriately considered in computing
SSC ITS probability of failure during a
seismic event.
Response. The example of Appendix
A is based on a hypothetical seismic
hazard curve selected only for
illustrative purpose. However, for the
development of the Yucca Mountain
site-specific mean seismic hazard curves
(Reference, Section 6.4), DOE’s current
approach evaluates the potential of
closely spaced, recurring, seismic events
by considering simultaneous multiple
ruptures on parallel dipping faults, and
increasing the ground motion
parameters for a given probability of
exceedance value. Since the effects of
the closely spaced, recurring, seismic
events are considered in the seismic
hazard curve, staff believes that the
ISG–01 methodology would result in an
appropriate value of the failure
probability of an SSC ITS, and that ISG–
01 or the YMRP need not be revised.
[Reference: Civilian Radioactive Waste
Management System, Management and
Operating Contractor (CRWMS, M&O), 1998,
Probabilistic Seismic Hazard Analyses for
Fault Displacement and Vibratory Ground
Motion at Yucca Mountain, Nevada (I. G.
Wong and J. C. Stepp, coordinators), report
prepared for U. S. Geological Survey, 3
Volumes]
No changes were made to the ISG as
a result of this comment.
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16. Comment. It is unclear to the
commenter whether the guidance
directs NRC staff to use the suggested
methodology or merely offers an
alternative among possible methods. To
reduce uncertainty, the commenter
suggests that it would be helpful if NRC
provided explicit guidance as to how
the selection of an appropriate
methodology would be made, and
when, if at all, a given methodology
might be unacceptable for use. The
commenter believes that the discretion
in choice of methods appears to
introduce unwarranted ambiguity and
uncertainty.
Response. An ISG provides guidance
to NRC staff on suggested methodologies
to use during the review of a potential
license application, and do not imply a
preferred methodology that an applicant
must use. The review approach in an
ISG provides a framework for staff to
conduct an efficient review, consistent
with regulatory requirements. DOE has
the option of proposing alternative
methodologies to comply with the
regulations, which the staff would
evaluate during its review of the License
Application. Methodologies that
demonstrate compliance with the
regulations, and have adequate
technical bases, would be acceptable for
staff review.
No changes were made to the ISG as
a result of this comment.
Jon
Chen, Project Manager, Division of
High-Level Waste Repository Safety,
Office of Nuclear Material Safety and
Safeguards, U.S. Nuclear Regulatory
Commission, Washington, DC 20005–
0001 (Telephone: (301) 415–5526; fax
number: (301) 415–5399; e-mail:
jcc2@nrc.gov); Mahendra Shah, Senior
Level Advisor, Division of High-Level
Waste Repository Safety, Office of
Nuclear Material Safety and Safeguards,
U.S. Nuclear Regulatory Commission,
Washington, DC 20005–0001
(Telephone: (301) 415–8537; fax
number: (301) 415–5399; e-mail:
mjs3@nrc.gov)
FOR FURTHER INFORMATION CONTACT:
Dated at Rockville, Maryland, this 22nd
day of September 2006.
For the Nuclear Regulatory Commission.
N. King Stablein,
Chief, Project Management Section B,
Division of High-Level Waste Repository
Safety, Office of Nuclear Material Safety and
Safeguards.
[FR Doc. E6–16017 Filed 9–28–06; 8:45 am]
BILLING CODE 7590–01–P
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NUCLEAR REGULATORY
COMMISSION
Notice of Availability of Draft Interim
Staff Guidance Document HLWRS–
ISG–02, Preclosure Safety Analysis—
Level of Information and Reliability
Estimation
Nuclear Regulatory
Commission.
ACTION: Notice of availability.
AGENCY:
Jon
Chen, Project Manager, Project
Management Section B, Division of
High-Level Waste Repository Safety,
Office of Nuclear Material Safety and
Safeguards, U.S. Nuclear Regulatory
Commission, Washington, DC 20005–
0001. Telephone: (301) 415–5526; fax
number: (301) 415–5399; e-mail:
jcc2@nrc.gov.
FOR FURTHER INFORMATION CONTACT:
SUPPLEMENTARY INFORMATION:
I. Introduction
The Yucca Mountain Review Plan
(YMRP) (July 2003, NUREG–1804,
Revision 2) provides guidance for U.S.
Nuclear Regulatory Commission (NRC)
staff to evaluate a U.S. Department of
Energy license application for a geologic
repository. NRC has prepared Interim
Staff Guidance (ISG) to provide
clarifications or refinements to the
guidance provided in the YMRP. NRC is
soliciting public comments on Draft
HLWRS–ISG–02, which will be
considered in the final version or
subsequent revisions to HLWRS–ISG–
02.
II. Summary
The purpose of this notice is to
provide the public with an opportunity
to review and comment on draft
HLWRS-ISG–02, which is to
supplement the YMRP for the NRC staff
review of design and operation
information and reliability estimates
required for the preclosure safety
analysis. This ISG supplements sections
2.1.1, 2.1.1.2, 2.1.1.4, 2.1.1.6, and 2.1.1.7
of the YMRP. This guidance also
provides examples that illustrate
commonly used approaches for
estimating reliability and the level and
types of supporting design and
operation information that would be
necessary for structures, systems, and
components (SSCs) at the geologic
repository operations area. A sufficient
level of information and adequate
technical bases for reliability estimates
are needed to demonstrate compliance
with the performance objectives in Code
of Federal Regulations, Title 10, Part 63,
Section 63.111 (10 CFR 63.111).
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[Federal Register Volume 71, Number 189 (Friday, September 29, 2006)]
[Notices]
[Pages 57579-57584]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E6-16017]
-----------------------------------------------------------------------
NUCLEAR REGULATORY COMMISSION
[HLWRS-ISG-01]
Review Methodology for Seismically Initiated Event Sequences;
Availability of Final Interim Staff Guidance Document
AGENCY: Nuclear Regulatory Commission.
ACTION: Notice of availability.
-----------------------------------------------------------------------
SUMMARY: The Nuclear Regulatory Commission (NRC) is announcing the
availability of final interim staff guidance (ISG) document, ``HLWRS-
ISG-01, Review Methodology for Seismically Initiated Event Sequences,''
and NRC responses to the public comments received on that document. The
ISG clarifies or refines the guidance provided in the Yucca Mountain
Review Plan (YMRP) (NUREG-1804, Revision 2, July 2003). The YMRP
provides
[[Page 57580]]
guidance to NRC staff for evaluating a potential license application to
receive and possess high-level radioactive waste at a geologic
repository constructed or operated at Yucca Mountain, Nevada.
ADDRESSES: The document HLWRS-ISG-01 is available electronically at
NRC's Electronic Reading Room, at https://www.nrc.gov/reading-rm/
adams.html. From this site, you can access NRC's Agencywide Documents
Access and Management System (ADAMS), which provides text and image
files of NRC's public documents. The ADAMS accession number for the ISG
is ML062650140. 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 1-800-397-4209, or (301)
415-4737, or (by e-mail), at pdr@nrc.gov.
This document may also be viewed electronically on the public
computers located at NRC's PDR, Mail Stop: O1F21, One White Flint
North, 11555 Rockville Pike, Rockville, MD 20852. The PDR reproduction
contractor will copy documents, for a fee.
NRC RESPONSES TO PUBLIC COMMENTS ON HLWRS-ISG-1: In preparing final
HLWRS-ISG-01, ``Review Methodology for Seismically Initiated Event
Sequences,'' ADAMS ML062650140, the NRC staff reviewed and considered
23 comments received from five different organizations during the
public comment period. One commenter had 12 comments recommending
specific clarifying changes to the ISG. One commenter questioned NRC
using the ISG to clarify its regulatory intent, instead of addressing
the issue of seismically initiated event sequences, more appropriately,
in the YMRP. Two commenters questioned whether the ISG sets forth a
more stringent standard for the seismic design of repository surface
facilities than the existing criteria for reactors. One commenter was
concerned that a specific methodology described in the ISG would bias
the NRC staff's review against other methodologies that the U. S.
Department of Energy (DOE) may propose that provide equal or better
protection of public health and safety. One commenter was concerned
that the specific methodology proposed in the ISG lacks both precedent
and scientific support. Two commenters were concerned that the ISG
methodology may not produce accurate results over the 100-year plus
operating life of the Yucca Mountain repository preclosure operating
period. Two commenters raised questions as to whether NRC has
adequately considered the geometric consequence of closely spaced,
recurring seismic events, in determining the seismic hazard and related
failure probability of a structure, system, or component (SSC)
important to safety (ITS). One commenter states that ``the ISG totally
ignores the existence of Section 63.102(f) of the regulation.'' The
following discussion indicates how the comments were addressed, and the
changes, if any, made to the ISG as a result of the comments.
Line numbers in the following comments refer to the draft HLWRS-
ISG-01, ADAMS ML061170532, which was made available for public comment
on May 22, 2006 (71 FR 29369).
1. Comment. The commenter recommends that the sentence starting at
Line 38 be re-phrased as: ``The mean fragility curve for an SSC ITS may
be estimated using: (1) Probability density functions for controlling
parameters in a Monte Carlo analysis; (2) simplified methods outlined
in Section 4 of Electric Power Research Institute, TR-103959 (Ref. 2);
(3) a method that uses the Conservative Deterministic Failure Margin
methodology to determine the 1percent probability of failure, and an
estimate of the composite logarithmic standard deviation, as described
by Kennedy (2001, pp. 44 to 45) and Ravindra (2006, p. 132); or (4)
other methods that capture appropriate variability and uncertainty in
parameters used to estimate the capacity of the SSCs ITS to seismic
events.
Response. NRC regulations grant DOE broad flexibility in choosing a
method or methods for preclosure safety analysis of hazards at the
geologic repository operations area (GROA). Although NRC staff has
stated some example methods, in the ISG, for estimating the fragility
curve, this does not imply that alternative methods would be
unacceptable for demonstrating compliance with regulatory requirements.
DOE may use an alternative method, if sufficient technical basis for
the use of the method is provided.
No changes were made to the ISG as a result of this comment.
2. Comment. The commenter recommends that the following sentence be
added at the end of the sentence on line 43:
``Where appropriate, assessment of fragility for an SSC may be
based on fragility values for an identical or similar component as
found in the literature.''
Response. NRC agrees with the commenter that the fragility data for
an SSC, developed and documented in databases and used at other
facilities, may be used to estimate fragility for the SSCs at the
repository, if the data are shown to be applicable to the repository
SSCs.
The ISG has been revised to add the following at the end of the
sentence on Line 43:
``An estimate of fragility for an SSC may be based on fragility
values for an identical or similar component as found in the
literature, provided technical bases for the relevance of the data
to the SSC under consideration are established.''
3. Comment. The commenter recommends that an explanation be
provided to address why the selection of the slope (Lines: 235 to 237,
240 to 241: Page: 8) is appropriate. This explanation may include, for
example, that this portion of the hazard curve was selected if it were
the interval where the dominant contribution to risk arises. Text could
be added at the end of the sentence on Line 241:
``The slope should be selected to focus on the portion of the
curve where risk is expected to dominate the convolution.''
Response. NRC agrees with the commenter that an explanation for the
selection of the slope between probabilities of exceedance of
10-6 and 10-5 should be added in the ISG.
The ISG has been revised to add the following at the end of the
sentence on Line 241:
``This slope was selected to represent the hazard accurately at
probabilities of exceedance values close to the target annual
threshold probability of 10-6 because this portion of the
hazard curve may have a significant contribution to the risk.''
4. Comment. The commenter suggests replacing the sentence starting
on Line 263, with the sentence: ``For the purposes of illustration, a
single response frequency of 10 hertz (Hz) is assumed for this
evaluation.'' The commenter also suggests that an explanation of why a
single frequency is appropriate should be added.
Response. NRC believes that the essence of the comment, with the
suggested change to the ISG, is adequately responded to by the
sentences in lines 262 to 264 of the ISG. These sentences state that
the evaluation typically would be performed at appropriate structural
frequencies, based on the dynamic characteristics of the SSC, and that
example evaluation is performed at a single frequency of 10 hertz. A
single frequency was chosen in the example for illustration purposes
only. As stated in the sentence in line 261, the evaluation typically
would have to be performed for a number of structural frequencies of an
SSC, based on its dynamic characteristics, to
[[Page 57581]]
appropriately assess the probability of failure of an SSC during a
seismic event.
No changes were made to the ISG as a result of this comment.
5. Comment. The commenter suggests that text be added to include
discussion of other non-seismic factors that may influence/mitigate the
probability of occurrence of the event sequence. At line 262, a
sentence should be inserted to read:
``Other non-seismic factors such as residency times, targeting
factors, operational states, and design constraints, which may also
influence the probability of occurrence of the complete event
sequence, are not considered in this example.''
Response. NRC agrees with the commenter that in the example, design
constraints, such as the probability of failure of the canister during
a potential drop event, are not considered. This is indicated in Lines
276 to 277 of the ISG, and in the clarifying statement added in the ISG
in response to comment 10. NRC believes that the clarifying statement
recognizes that if the canister breach probability (given a drop) is
demonstrated to be less than 1.0, the appropriate conditional
probability of breach may be factored into the quantification of the
event sequence. Therefore, NRC believes that a change to the ISG to
clarify this factor in determining the probability of occurrence of the
event sequences is not necessary. Other non-seismic factors mentioned
in the comment appear to be related to the duration of operations at
the proposed Yucca Mountain repository. NRC would need specific
information on the Yucca Mountain repository operations and the
technical bases for determining the values of these factors, to judge
whether these factors are appropriate and can be used to calculate
event sequence probability of occurrence in the preclosure safety
analysis. NRC will review the use of these factors and their technical
bases and make a determination of their acceptability during the
potential future review of the DOE License Application for the proposed
Yucca Mountain repository.
No changes were made to the ISG as a result of this comment.
6. Comment. The commenter recommends that the assumption made in
the computation be clarified, and that each branch in the sequence be
addressed in the description (Lines: 308 to 323: Page: 12). For
instance, at the end of the sentence ending on Line 310, the text
should be expanded to mention the other branches:
``Tracing Sequence 3 across the event tree shown in Figure B-1,
this sequence also includes the STR-SHWL success branch and the
assumed failure of the canister (CANIS-BRCH) * * *'' Additional text
on Lines 310 to 323 should include: ``* * * the STR-SHWL success
probability is the complement of the fragility of the failure branch
* * *'' and ``* * * Therefore, the combined fragility of the three
systems in the event sequence can be obtained by * * *.''
Response. NRC agrees with the commenter that the Event Sequence 3,
as shown in Figure B-1, implies that the concrete shear wall provides a
confinement barrier to the release of radioactive materials before they
pass through the Heating, Ventilation and Air-Conditioning (HVAC)
system. However, for illustration purposes only, it was assumed in the
example that, if the HVAC duct anchor system fails, all radioactive
materials released because of the canister breach would be discharged
through the HVAC system. To clarify this assumption, the ISG has been
revised as follows:
Add the following at the end of the sentence in Line 309:
``For simplicity, it is assumed, in this example, that if the
HVAC duct anchor system were to fail, all radioactive materials
released because of the potential canister breach would be
discharged through the HVAC system, and that the concrete shear wall
would be unable to provide a barrier to the release of radioactive
materials.''
7. Comment. The commenter suggests that Figure B-1 be revised for
clarity, making the figure consistent with conventions for the
construction of event trees in other NRC documents, such as NUREG-2300.
The following changes are suggested to Figure B-1:
(a) The figure be revised to indicate that the initiating event
of the sequence is an earthquake;
(b) The figure heading be revised to state the event in terms of
success;
(c) The missing branch be shown for the event that the crane
does not drop the waste form.
(d) The probability of canister breach, which has been assumed
to be 1.0, be indicated.
Response. NRC agrees with the suggested change in item (b), above,
regarding revision of the figure headings and stating the event in
terms of success, and has revised Figure B-1. Staff, however, does not
agree with the other suggested changes because the title of the figure
identifies the event sequence as initiated by a seismic event. This is
also consistent with Section 11.2.6.2 of NUREG-2300. In addition,
adding a success path for the crane not dropping the waste form would
be superfluous to this example, and would not add any value to the
illustration of the procedure for event sequence probability
calculation. The probability of canister breach assumed as 1.0 is
stated in section B of Appendix B.
Figure B-1 has been revised as a result of this comment.
8. Comment. Assuming that the text in lines 220 to 222 has broader
applicability than just as part of the example, the commenter suggests
that the sentence starting on Line 220 be deleted from Appendix A,
moved to the Discussion section on page 1, and inserted into the text
at Lines 54 to 63. The commenter also suggests changes to the text for
insertion into the Discussion section on page 1, in comment 9.
Response. NRC agrees with the comment. The ISG has been revised as
follows:
(a) The sentence starting on Line 220 and ending on Line 222,
``The technical basis * * * staff review.'', has been deleted.
(b) The following has been added at the end of the sentence on Line
57:
``Technical bases for the development of the SSC ITS fragility
curves should be available for staff review.''
9. Comment. The commenter suggests that, the following sentence
consistent with the Comment 8, should be inserted into the Discussion
section on page 1 at Lines 54 to 63:
``It is necessary in developing seismic fragilities that the
technical basis for the development of the applicable fragility
parameters be available for staff review.''
Response. NRC agrees with the essence of the comment. The ISG has
been revised as shown in NRC staff response to comment 8, item (b).
10. Comment. The commenter recommends adding the following phrase
to the end of Line 277:
``* * * and it is assumed that probability of breach is 1.0 in
all cases''. In addition, the commenter recommends adding, in Figure
B-1, ``(Pf = 1.0),'' on the branch indicating potential for breach.
The commenter also recommends adding text to state that when the
probability of a breach (given a drop) is demonstrated to be less
than 1.0, the appropriate conditional probability of breach may be
factored into the quantification of the event sequence.
Response. NRC agrees with the comment. The ISG has been revised to
clarify that, for the example in Appendix B, it is assumed that the
canister probability of failure (given a drop) is 1.0. The comment
regarding the use of appropriate conditional probability of canister
failure, in the event sequence probability calculation, has been
addressed in response to comment 5.
The ISG has been revised to add the following at the end of the
sentence in Line 277:
[[Page 57582]]
``It is assumed that the canister probability of failure, given
a drop, is 1.0.''
11. Comment. The commenter suggests adding the following text in
the sentence starting on Line 36:
``As a conservative assessment of probability, the probability
of occurrence of an event sequence leading to an SSC ITS failure, or
seismic performance, can be determined by * * *''
Response. NRC agrees with the essence of the comment, and has added
a new sentence to reflect the comment. The ISG has been revised to add
the following sentence in Line 36:
``As a conservative assessment of the probability of occurrence
of an event sequence, a single SSC ITS may be considered, instead of
all SSCs ITS in the event sequence.''
12. Comment. The commenter suggests that a brief statement be added
at the end of line 232 and in Appendix B, as follows:
``Computations shown in the appendix can be performed either by
hand computations or through the use of computer codes. A number of
computer codes are available that can be used for probability
computations.''
Response. NRC agrees with the commenter that computations for the
event sequence probabilities can be performed either by hand
computations or through the use of computer codes. However, these
options are available to the applicant for any calculations. Although
the details of associated quality assurance requirements may be
different for the computational method selected, the overall staff
review strategy for the DOE analysis is not affected significantly by
the computational method selected by DOE. Therefore, staff does not see
the need to revise the ISG.
No changes were made to the ISG as a result of this comment.
13. Comment. The commenter refers to NRC Chairman Dale E. Klein's
statement, on July 1, 2006, that regulatory stability is a crucial
element in ensuring that NRC can complete its work in a timely manner,
and states that HLWRS ISG-01 has the potential to create regulatory
instability. Accordingly, the commenter encourages NRC to take
advantage of the opportunity afforded by this comment period to
reconsider issuing this ISG and to instead address the issue of
seismically initiated event sequences, more appropriately, in the YMRP.
The commenter is recommending this course of action for the following
five reasons:
(a) ISG is not the most effective means for NRC to clarify its
regulatory intent and could lead to unforeseen consequences due to
inadequate review (including not being reviewed by the Commission
itself).
(b) Use of an ``Interim Guidance,'' a vehicle that was meant to
address emerging issues affecting multiple licensed activities, is
unnecessary in a situation where there is only a single potential
licensee that is not currently conducting any licensed activities.
(c) Draft HLRWS ISG-01 lacks safety focus in that it sets forth a
more stringent standard for the seismic design of repository surface
facilities than currently exists for reactors, without recognizing the
comparatively lower level of risk associated with the repository
facilities. In doing this, HLRWS ISG-01 directly contradicts the very
regulation (10 CFR Part 63) that it seeks to inform.
(d) Providing guidance to staff that assumes a specific methodology
for demonstrating compliance with 10 CFR 63.111 is likely to bias the
staff's review against other methodologies, that DOE may propose, which
provide equal or better protection of public health and safety.
Furthermore, giving DOE the opportunity to first propose an acceptable
method for meeting the regulation would allow for a more independent
NRC review--avoiding a situation where NRC is both telling DOE how to
demonstrate compliance and then determining if compliance was
demonstrated as instructed.
(e) The specific methodology proposed in this draft ISG lacks both
precedent and scientific support.
Response. Responses to each of the commenter's reasons are provided
below:
(a) In the commenter's view, the ISG is not an effective means for
NRC to clarify its regulatory intent and could lead to unforeseen
consequences because of inadequate review (including not being reviewed
by the Commission itself).
The ISG reflects a focused revision of the YMRP, with the scope of
the revision limited to a specific technical issue. The ISG process
allows for the rapid identification and resolution of specific
technical issues that emerge as a result of staff interaction, with
DOE, in preparation for the future License Application review. To
increase regulatory efficiency and enhance clarity of communication
with DOE and the public, NRC anticipates providing incremental updates
to the YMRP in the form of ISGs. NRC believes it is unnecessary and
inefficient to republish the YMRP, given the narrow scope of the
technical issue addressed in the ISG. If re-publication of the YMRP is
warranted (e.g., due to a major rule change or accumulation of a number
of ISGs), staff will be able to insert the appropriate text directly
from the ISG into the YMRP. The ISG remains available to provide
background discussion and examples, to supplement text, in the YMRP, at
a level of detail not normally found in a Standard Review Plan (SRP).
Thus, staff sees the ISG process as an effective, efficient, and
appropriate means for revising or supplementing the YMRP.
An ISG provides guidance to NRC staff on approaches to use during
the review of a potential license application. ISG guidance is for
illustration purposes only, and does not imply a preferred method or an
approach that an applicant must use. An ISG's review approach provides
a framework for staff to conduct an efficient review, consistent with
regulatory requirements. ISGs, that are revisions or supplements to the
SRPs, are issued at the NRC Office Division level, because SRPs do not
represent regulatory commitments, or staff interpretations. During the
ISG development process, the technical and regulatory basis for the ISG
is thoroughly reviewed by appropriate NRC technical, management, and
legal staff. Also, the public and shareholders are informed of a
proposed draft ISG and afforded the opportunity to comment. Comments
from the public and stakeholders are considered in developing the final
ISG.
No changes were made to the ISG as a result of this comment.
(b) In the commenter's view, ISGs are not necessary for the Yucca
Mountain project because DOE is the only potential licensee for the
proposed repository, and no licensing activities are being conducted
currently. Although it is true that DOE is the only potential licensee
and no licensing activities are currently underway, important technical
issues continue to be identified in the complex, one-of-a-kind Yucca
Mountain project during the prelicensing interaction with DOE. As these
issues are being resolved, the ISG process provides an effective,
efficient, and appropriate means for staff to revise or supplement the
YMRP, as discussed in response to comment 13(a). The ISG process also
allows staff to communicate with potential licensees on the scope of
the staff reviews on specific technical issues, as NRC staff prepares
to review the potential License Application in an effective and timely
manner.
No changes were made to the ISG as a result of this comment.
(c) In the commenter's view, ISG-01 lacks safety focus and sets
forth a more stringent standard for the seismic design
[[Page 57583]]
of repository surface facilities than for reactors even though the
repository facility has a lower level of risk, which appears
contradictory to the intent of 10 CFR Part 63. The commenter also
questions the purpose of 10 CFR 63.102(f) and how it is accounted for
in the draft HLWRS-ISG-01. Another commenter made a similar statement.
NRC does not agree with the commenter that the ISG-01 proposed
methodology for seismically initiated event sequences sets forth a more
stringent standard for the seismic design of repository facilities than
for reactors. NRC also does not agree that the ISG-01 contradicts the
intent of Part 63. The methods discussed in the draft ISG do not
mandate seismic design requirements, but present approaches that NRC
staff could use to review the performance of SSCs ITS for seismically
initiated event sequences, as required in Part 63.
The preclosure compliance requirements in Part 63 are performance-
based, in that instead of specifying specific design loads and
corresponding acceptance criteria (i.e., codes/standards) the
regulations in 10 CFR 63.111, for the GROA, specify radiological dose
limits to the public and workers. In the preclosure safety analysis
(PCSA), DOE must demonstrate that the GROA design will meet these dose
limits, taking into consideration credible event sequences.
The ISG-01 provides a methodology to determine if a seismically
initiated event sequence is a Category 2 event sequence, as defined in
10 CFR 63.2, or if it is beyond Category 2 and can be screened out from
further consideration. If the event sequence is determined to be a
Category 2 event sequence, DOE has to demonstrate that the dose limit
of 5 roentgen equivalent man (rem) at any point on the boundary of the
site is met. These performance-based requirements in Part 63
necessarily result in a different type of compliance demonstration than
is traditionally used for reactor licensing.
For reactors, a seismic event is directly related to the
characteristics of a specified safe shutdown earthquake (10 CFR Part
50, Appendix S), which is used as the design basis for each of the
safety-related SSCs, and demonstration of compliance with regulations.
In contrast, Part 63 does not specify seismic or other design bases or
SSCs, but instead requires consideration of credible event sequences
and their potential consequences. The guidance in the draft ISG shows
how the fragilities of one or more SSCs in an event sequence can be
combined with the seismic hazard curve to determine the likelihood of
an entire event sequence, which is the metric used for compliance in
Part 63. Section 63.102(f), which allows initiating events to be
considered based on precedents adopted for nuclear facilities with
comparable or higher risks, was not used in the ISG-01 because the
compliance demonstration for Part 63 requires safe performance of SSCs
in seismically initiated event sequences, instead of a single
initiating seismic event (i.e., safe-shutdown earthquake) that is
traditionally used as a design basis in reactor licensing.
DOE will need to design to a level of performance sufficient to
meet the requirements of Part 63, for seismically initiated event
sequences. DOE is given broad flexibility in selecting a preferred
design basis, and determining the degree of defense-in-depth contained
within the GROA system. Although DOE must provide the basis for its
proposed designs, compliance with Part 63 will be determined by the
performance of the design during credible seismically initiated event
sequences, not by adherence to a predetermined design basis for a
seismic event.
No changes were made to the ISG as a result of this comment.
(d) In the commenter's view, the specific methodology in the ISG-01
may bias the staff's review against other methodologies that DOE may
propose, even if these alternatives provide equal or better protection
of public health and safety. The commenter also raises the concern that
NRC should not dictate to DOE how to demonstrate compliance with
regulations because it does not allow for a more independent review of
the future DOE License Application. NRC does not agree with the comment
that providing a methodology for seismically initiated event sequences
in ISG-01 may preclude DOE from proposing other methodologies for
complying with Part 63. Similar to the YMRP, ISGs are prepared to
provide guidance to the staff for review of any future License
Application, from DOE, for the proposed Yucca Mountain repository, and
are not mandatory. DOE has the option of proposing alternative
methodologies to comply with the regulations, which the staff would
evaluate during its review of the License Application. As discussed in
response to Comment 1, presenting an example methodology in an ISG does
not imply a preference for that method in licensing, and does not
restrict the ability of an applicant to use an alternative method.
No changes were made to the ISG as a result of this comment.
(e) In the commenter's view, the specific methodology proposed in
the draft ISG-01 lacks both precedent and scientific support. The
commenter raises the concern that applying technical analysis to
seismic events with probability of exceedance lower than one in 10,000
per year to establish design bases is unprecedented, and that it would
result in stringent design criteria. Staff disagrees with the
commenter's concern because ISG-01 does not provide guidelines on the
design bases or design criteria for the SSCs, of the GROA, at the
repository, but provides one method for NRC staff to use in reviewing
demonstration of compliance with the performance requirements for the
SSCs in the PCSA. Additionally, the methodology proposed in the draft
ISG has precedent in the mixed-oxide fuel fabrication facility at the
Savannah River Site in South Carolina, where the applicant used a
methodology similar to the one outlined in the draft ISG to demonstrate
performance of the facility during seismic event sequences.
NRC disagrees with the comment that the methodology proposed in
ISG-01 lacks scientific support. The proposed ISG-01 methodology to
evaluate seismic performance of an SSC ITS is consistent with the
performance-based methodology in the consensus standard ASCE 43-05. The
methodology has the scientific support of the experts in the industry,
and is not beyond the state-of-the-art for performance evaluation of
SSCs for seismic hazard.
No changes were made to the ISG as a result of this comment.
14. Comment. Two commenters stated that NRC's decision to approve
the use of the methodology that is similar to the one outlined in ASCE
43-05 appeared to be based on the method's recent use in licensing of
the mixed-oxide fuel fabrication facility at the Savannah River Site.
The MOX facility has a projected operating life of 20-40 years and it
is assumed that the NRC operating license is for the same period of
time. The commenters are concerned about the ability of ASCE 43-05 to
appropriately account for uncertainty over the longer time-frame for
Yucca Mountain, given that the preclosure operating period for the
repository project could be 100 years or longer. The commenter adds
that NRC should address this issue in the final staff guidance.
Response. The commenters raise a concern that the ISG-01
methodology, as suggested by ASCE 43-05, may not produce accurate
results over a potential 100-year or longer operating life of the Yucca
Mountain repository preclosure
[[Page 57584]]
operating period. The preclosure operating period of the Yucca Mountain
repository may affect the ISG-01 methodology results in two ways: (i)
In categorization of seismically initiated event sequences (e.g., one
chance in 10,000 of occurrence during the preclosure period specified
in Part 63 for category 2 event sequences); and (ii) in development of
the SSCs ITS seismic fragility curves, with potential changes in
material properties resulting from degradation during the preclosure
period. Staff believes that the uncertainties, considered in the
seismic hazard and SSCs ITS fragility curves development, would
sufficiently account for potential materials degradation during the
preclosure period.
No changes were made to the ISG as a result of this comment.
15. Comment. Two commenters stated that the example provided in
Appendix A raises questions as to whether NRC has adequately considered
the geometric consequence of closely spaced, recurring, seismic events
in determining the mean seismic hazard and related failure probability
of an SSC ITS. HLWRS-ISG-01 and/or the YMRP may need to be revised to
ensure that such characteristics of seismic hazard and related failure
probability are appropriately considered in computing SSC ITS
probability of failure during a seismic event.
Response. The example of Appendix A is based on a hypothetical
seismic hazard curve selected only for illustrative purpose. However,
for the development of the Yucca Mountain site-specific mean seismic
hazard curves (Reference, Section 6.4), DOE's current approach
evaluates the potential of closely spaced, recurring, seismic events by
considering simultaneous multiple ruptures on parallel dipping faults,
and increasing the ground motion parameters for a given probability of
exceedance value. Since the effects of the closely spaced, recurring,
seismic events are considered in the seismic hazard curve, staff
believes that the ISG-01 methodology would result in an appropriate
value of the failure probability of an SSC ITS, and that ISG-01 or the
YMRP need not be revised.
[Reference: Civilian Radioactive Waste Management System,
Management and Operating Contractor (CRWMS, M&O), 1998,
Probabilistic Seismic Hazard Analyses for Fault Displacement and
Vibratory Ground Motion at Yucca Mountain, Nevada (I. G. Wong and J.
C. Stepp, coordinators), report prepared for U. S. Geological
Survey, 3 Volumes]
No changes were made to the ISG as a result of this comment.
16. Comment. It is unclear to the commenter whether the guidance
directs NRC staff to use the suggested methodology or merely offers an
alternative among possible methods. To reduce uncertainty, the
commenter suggests that it would be helpful if NRC provided explicit
guidance as to how the selection of an appropriate methodology would be
made, and when, if at all, a given methodology might be unacceptable
for use. The commenter believes that the discretion in choice of
methods appears to introduce unwarranted ambiguity and uncertainty.
Response. An ISG provides guidance to NRC staff on suggested
methodologies to use during the review of a potential license
application, and do not imply a preferred methodology that an applicant
must use. The review approach in an ISG provides a framework for staff
to conduct an efficient review, consistent with regulatory
requirements. DOE has the option of proposing alternative methodologies
to comply with the regulations, which the staff would evaluate during
its review of the License Application. Methodologies that demonstrate
compliance with the regulations, and have adequate technical bases,
would be acceptable for staff review.
No changes were made to the ISG as a result of this comment.
FOR FURTHER INFORMATION CONTACT: Jon Chen, Project Manager, Division of
High-Level Waste Repository Safety, Office of Nuclear Material Safety
and Safeguards, U.S. Nuclear Regulatory Commission, Washington, DC
20005-0001 (Telephone: (301) 415-5526; fax number: (301) 415-5399; e-
mail: jcc2@nrc.gov); Mahendra Shah, Senior Level Advisor, Division of
High-Level Waste Repository Safety, Office of Nuclear Material Safety
and Safeguards, U.S. Nuclear Regulatory Commission, Washington, DC
20005-0001 (Telephone: (301) 415-8537; fax number: (301) 415-5399; e-
mail: mjs3@nrc.gov)
Dated at Rockville, Maryland, this 22nd day of September 2006.
For the Nuclear Regulatory Commission.
N. King Stablein,
Chief, Project Management Section B, Division of High-Level Waste
Repository Safety, Office of Nuclear Material Safety and Safeguards.
[FR Doc. E6-16017 Filed 9-28-06; 8:45 am]
BILLING CODE 7590-01-P
