[Federal Register Volume 69, Number 212 (Wednesday, November 3, 2004)]
[Notices]
[Pages 64115-64116]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-24494]
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NUCLEAR REGULATORY COMMISSION
Draft Appendix C (DG-1138) to Regulatory Guide 1.200, ``An
Approach for Determining the Technical Adequacy of Probabilistic Risk
Assessment Results for Risk-Informed Activities,'' Workshop
The U.S. Nuclear Regulatory Commission (NRC) has issued draft
Appendix C, ``NRC Staff Position on ANS External Hazards PRA Standard''
in August 2004. This Appendix will be
[[Page 64116]]
part of Regulatory Guide 1.200, ``An Approach for Determining the
Technical Adequacy of Probabilistic Risk Assessment Results for Risk-
Informed Activities'' which was issued for trial use. The Appendix C
was issued for public comment on August 31, 2004, and is available
under ADAMS Accession Number ML042430314. Revision 1 to RG 1.200, which
will include a final draft Appendix C, will be issued next year for
public comment. Regulatory Guides (RGs) are developed to describe and
make available to the public such information as methods acceptable to
the NRC staff for implementing specific parts of the NRC's regulations,
techniques used by the staff in evaluating specific problems or
postulated accidents, and data needed by the staff in its review of
applications for permits and licenses.
This draft Appendix C is being developed to provide the staff's
preliminary position on the American Nuclear Society, (ANS) Standard,
External-Events Probabilistic Risk Assessment (PRA) Methodology. This
draft Appendix C has not received complete staff approval and does not
represent an official NRC staff position. It is the NRC's intent to
update Appendix C when a revised ANS standard on external events is
published. Therefore, if a revision of the current ANS standard impacts
the staff position, this Appendix C will be revised.
The NRC will conduct a workshop on November 9, 2004, to be held in
room O4B6 at NRC headquarters, 11545 Rockville Pike, Rockville,
Maryland. The purpose of the workshop is to facilitate the comment
process. In the workshop, the staff will discuss the staff's response
to the public comments received and the basis for the staff's position,
and answer questions. A preliminary agenda is attached. The staff is
also requesting comments on the following general issues and two
specific issues. The general issues are:
The intent was that the ANS standard be seamless with the
American Society of Mechanical Engineers (ASME) PRA standard for
internal events. However, this has not been achieved for the following
reasons:
In the ASME Standard, the word ``shall'' is only used in high
level requirements, and permissive words such as ``should'' or ``may''
are not used in any requirements. The ANS Standard on external-events
uses permissive words in both high level and supporting requirements.
Permissive words are not to be used because they cannot be used to
define a minimum requirement.
The ANS Standard interprets the use of supporting requirements
that cut across capability categories in a different manner from the
ASME Standard (see discussion in Section 1.4 of the ANS Standard). In
the ASME Standard, a requirement that is the same for more than one
capability category, is to be interpreted as a pass/no-pass requirement
with no requirement to allocate a capability category.
[diams] The organization of the ANS Standard is different from that
of the ASME Standard. In the ASME Standard the applications chapter is
Chapter 3, whereas in the ANS Standard it is Chapter 6.
[diams] Some definitions are not consistent with those in the ASME
Standard.
The staff considers the use of explanatory notes is
helpful in principle. However, several of the notes contain what the
staff interprets as requirements (see example, SR WIND-A1).
The staff has identified several missing supporting
requirements. These include, for each of the hazards, requirements to
identify the Structures Systems and Components (SSCs) that are critical
to plant safety, SSCs that are vulnerable to the hazard being
evaluated, identification of specific failure modes, and identification
of the modification of PRA logic to model these failures.
In addition to these general issues, there are two specific issues
on which the staff requests comment.
Section 3.4 of the ANS Standard addresses screening of
external hazards. In Section 3.4.2, three fundamental (sic)
quantitative screening criteria are introduced, that focus on core
damage frequency (CDF). The last paragraph recognizes that large early
release frequency (LERF) should also be considered in the screening but
does not suggest additional requirements. One approach is to lower the
numerical criteria (e.g., in REQ.EXT-C1) to result in screening at a
CDF of 1E-07 rather than 1E-06. Is this an acceptable approach, or are
there alternative approaches based on a more qualitative approach
dealing with the releases?
Appendix D in the ANS Standard is a nonmandatory appendix
that provides guidance on uses of a seismic margins assessment with
enhancements. The seismic margin approach, while can be used for
certain applications, is not a PRA. Since this standard is providing
requirements for an external events PRA, the staff takes objection to
this appendix. The staff believes the appropriate place to provide its
position on this appendix would be in the NUREG being prepared by the
Office of Nuclear Regulatory Research addressing the use of non-PRA
methods in risk-informed decision-making. Is this an appropriate
strategy?
For information about the draft Appendix C and the workshop,
contact Mr. A. Singh at (301) 415-0250; e-mail [email protected].
Although a time limit is given for comments on this draft Appendix
C, comments and suggestions in connection with items for inclusion in
guides, currently being developed, or improvements in all published
guides, are encouraged at any time.
Authority: (5 U.S.C. 552(a)).
Dated at Rockville, Maryland, this 26th day of October 2004.
For the Nuclear Regulatory Commission.
Charles E. Ader,
Director, Division of Risk Analysis and Applications, Office of Nuclear
Regulatory Research.
Public Workshop on Draft Appendix C ``NRC Staff Regulatory Position on
ANS External Hazards PRA Standard'' to Regulatory Guide 1.200 for Trial
Use ``An Approach for Determining the Technical Adequacy of
Probabalistic Risk Assessment Results for Risk Informed Activities''
November 9, 2004--10 a.m.-3 p.m. Room O-4B6
Preliminary Agenda
10 a.m.-10:15 a.m.
Introduction--NRC
10:15 a.m.-10:30 a.m.
Overview of Appendix C--NRC
10:30 a.m.-11 a.m.
Overall, general staff's response to public comments
11 a.m.-12 Noon
Detailed discussion on specific Comments
12 Noon-1 p.m.
LUNCH
1 p.m.-2 p.m.
Detailed discussion (cont'd)
2 p.m.-2:45 p.m.
Open Discussion
2:45 p.m.-3 p.m.
Wrap-up
3 p.m.
ADJOURN
[FR Doc. 04-24494 Filed 11-2-04; 8:45 am]
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