[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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