ML20217H885
| ML20217H885 | |
| Person / Time | |
|---|---|
| Issue date: | 05/28/1997 |
| From: | Apostolakis G Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-3025, NUDOCS 9708130322 | |
| Download: ML20217H885 (8) | |
Text
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.i ADVISORY COMMITTEE ON REACTOR SAFEGUARDS MEETING OF THE SUBCOMMITTEE ON PROBABILISTIC RISK ASSESSMENT MEETING MINUTES - AUGUST 7, 1996 ROCKVILLE, MARYLAND DiTAQD.2CIIDI The ACRS Subcommittee on Probabilistic Risk Assessment (PRA) met on August 7, 1996, at 11545 Rockville Pike, Rockville, MD, in Room T-193.
The purpose of this meeting was to discuss risk-based inservice testing (IST) and inservice inspection requirements (ISI), pilot applications for risk-informed and performance-based regulation, and issues identified in the Staff Requirements Memoranda (SRMs) dated May 15 and June 11, 1996, including the role of performance-based regulation in the PRA Implementation Plan.
The entire meeting was open to public attendance.
Mr. Michael T.
Markley was the cognizant ACRS staff engineer for this meeting.
The meeting was convened at 8:30 a.m. and adjourned at 6:06 p.m.
ATTENDEEE EL'i G. Apostolakis, Chairman D. Miller, Member I. Catton, Member R. Seale, Member M. Fontana, Member W. Shack, Member T. Kress, Member M. Markley, ACRS Staff W. Lindblad, Member R. Sherry, ACRS Fellow Principal NRC Sneakers E. Butcher, NRR*
T. King, RES G. Bagchi, NRR J. Murphy, RES M. Check, NRR A. Ramey-Smith, RES M. Cunningham, RES*
M. Rubin, NRR S. Dinsmore, NRR D. Wessman, NRR G. Holahan, NRR W. Hodges, RES T. Hsia, NRR d # 'N IndustrvfPublic Presenters
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- 5 K. Balkey, WOG*
D. Brewer, WOG A. Hackenrott, CEOG*
J. Haugh, EPRI*
gigga T.
Pietrangelo, NEI*
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R. Schneider, CEOG D. True, ERIN Engineering j;g;gg DE910NAT D NtIGINAt
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,.,3025 PDR
PRA Subcommittee 0-7-96 Minutes Office of Nuclear Reactor Regulation
- NRR Office of Nuclear Regulatory Research RES Westinghouse owners Group WOG Combustion Engineering Owners Group CEOG Electric Power Research Institute EPRI Nuclear Energy Institute NEI A complete list of meeting attendees is in the ACRS Office File, and will be made available upon request.
The presentation slides and handouts used during the meeting are attached to the office copy of these minutes.
Onenina Remarks Dr. George Apostolakis, Chairman of the Subcommittee, convened the meeting and stated that the purpose of this meeting was to discuss risk-based inservice testing and inservice inspection requirements, pilot applications for risk-informed and performance-based regulation and related matters.
He also stated that the Subcommittee would continue its discussion of issues identified in the SRMs dated May 15 and June 11, 1996, including the role of perf ormance-based regulation in the PRA Implementation Plan, plant-specific application of Safety Goals, and risk neutral versus the allowance for acceptable increases in risk.
He noted that the Subcommittee had previously met to discuss these matters on July 18, 1996.
Dr. Apostolakis stated that no written comments or requests for time to make oral statements were received from members of the public for this portion of the meeting.
However, he neted that several industry representatives would make presentations regarding these matters.
PreseD.tation by ACRS Pellow Mr. Rick Sherry, ACRS Fellow, provided a discussion on high level goal definition and r'isk allocation.
He discussed an approach for using top-down objectives for defining lower level safety goals and criteria.
Significant points made during his discussion include:
Top-level safety goal objectives for offsite consequences, containment performance (large radionuclide release), and core damage where the controlling safety goal quantitative health objectives (OHos) have the following subsidiary goals:
Large, early release frequency (LERF) of less than or equal to 1E-6/ reactor year;
s PRA Subcommittee 8-7-96 Minutes Core damage frequency -(CDP) of less than or equal to 1E-4/ reactor years and Conditional containment failure probability (CCFP) of less than or equal to 0.1 e
The CDP goal will be dominant for all sequences except those that are contrslied by the 0110 or LERF goal.
The LERF goal is difficult'to measure for existing plants, e
seismic sequences are often dominant contributors to risk.
Industry Presentation Mr.
Tony Pietrangelo of NEI coordinated the participation of industry representatives.
Messrs. Jack Haugh of EPRI and Doug True of ERIN Engineering provided supporting discussion for the NEI presentation.
Messrs. Alan !!ackenrott and Ray Schneider of the Combustion Engineering Owners Group also gave a presentation regarding their initiatives in the area of risk-informed Technical Specifications (TS).
Mr. Pietrangelo provided an overview of the EPRI PSA Applications Guide (PSAAG),
reviewed considerations for defining screening criteria, summarized the relationship between safety goals and oubsidiary safety objectives, and dtscussed possible screening criteria for permanent changes impacting CDF and LERF.
Significant points made during the discussion includes e
The PSA Applications Guide was issued in mid-1995 and supports the pilot projects and individual utility applications.
It is a suitable starting point for industry sponsored risk-informed submittals.
e Considerations in defining screening criteria include:
the relationship to safety goals and associated subsidiary safety objectives, figures of merit (CDF and LERF), approaches to defining screening criteria, and current PSA results.
The three-region approach (acceptable, further evaluation required, and non-risk significant) provided in the PSAAG.is an appropriate way to consider total risk in a apackaged" request.
-e The approach provided in the PSAAG maintains defense-in-depth
'and allows-for the presentation of uncertainty.
Mean values
-are acceptable screening criteria.
4
I e
PRA Subcommittee 8-7-96 Minutes 1
i Messrs. Hackenrott and Schneider presented an overview of the CEOG initiatives for risk-informed TS.
They discussed the joint application process (group submittal) being pursued on the part of
. ith CE reactors.
licensees who operate nuclear power plants w
significant points made during the discussion include:
7 e
The risk-informed pilot for TS seeks approval for extended allowed outage times (AOTs) and surveillance testing intervals (STIs).
Examples include proposed changes in AOTs for safety injection tank (SIT) testing, low pressure safety injection (LPSI) testing, and emergency diesel generators (EDGs).
- t l
e The CEOG has used plant cross-comparisons to establish the bases and rationale for these proposed changes.
These cross-
+
comparisons provide a method to certify proposed changes across a class of plants.
i ggLstaf f Presentation Messrs. Ed Butcher and Michael Cheok, NRR, provided an overview of the pilot applications.
They discussed the overall objectives of the pilots, the relationship between the Standard Review Plan (SRP) and Regulatory Guide, described the interaction with industry representatives regarding these initiatives, and summarized the technical issues in the context of each pilot.
The staf f solicited feedback from the ACRS regarding how to consider licensee submittals for plants with partial PRAs. The staf f summarized some general observations regarding the variability and completeness of PRAs associated with the pilot plantsi e
The staff concluded that a well-defined and documented peer review can help to ensure that PRA results and conclusions are aufficiently robust to be used to support decisionmaking.
[
- e Sensitivity studies on modelino and data issues will help to bound the results and conclusions, i
e Expert panels are useful in resolving differences and divergent views, e
sub-issues include truncation limits to derive stable results in terms of ranking order and the lack of modeling-and quantification of proposed changes.
The staff proposes to perform bounding analysis or other qualitative assessment to provide assurance for decisionmaking.
e The pilot-- approaches to addressing : uncertainty were still being evaluated nnd more work is needed to determine the extent of uncertainty analysis that should be required.
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PHA Subcommittee 5-8-7-96 c
Minutes e
The staff proposes to maintain defense-in-depth as a
deterministic consideration of integrated decisionmaking.
Messrs. Richard Wessman and Goutam Bagchi, NRR, presented a brief overview of the proposed risk-informed changes to the IST and ISI programs.
Significant points made during the discussion include:
Changes to the requirements for IST and ISI requires amendment to 10 CFR 50.55a.
s The proposed approaches provided in the pilot applications are based on risk significance.
o Interaction with the pilot plants is expected to help in the development of the SRP sections and Regulatory Guides, o
The staff is working closely with the American Society of Mechanical Engineers (ASME) who is developing code cases for risk-informed initiatives.
If approved, these code cases will be folded into the next revision of the ASME Code.
Mr.
Mark Cunningham and Ms.
Ramey-Smith provided a
general discussion of the policy and technical issues regarding the use of the Commission's Safety Goals to derive plant-specific appli-
- cations, the treatment of uncertainty, and the allowance for possible increases in risk.
Significant points made during the discussion include:
The staf f supports the use CDF and LERF as subsidiary safety goal objectives to derive acceptance guidelines for plant-specific applications, e
The staff supporto performing uncertainty analysis in assessing against guidelines (e.g.,
utilizing mean values).
The staf f of fered three options to consider in evaluating for possible increases in risk: plants that are much better than the guidelines, plants near the guidelines, and plants that do not meet the guidelines.
The staff raised an issue regarding how to handle a group or " package" of licensee requests where some proposed changes increase risk and others reduce risk.
Mr.
Gary Holahan provided an overview of performance-based regulation and relative to insights from the pilot applications.
Significant points made during the discussion include:
PRA is used in conjunction with deterministic assessments to focus licensee and regulatory attention on issues commensurate with their importance to safety.
o PRA Subcommittee 6-8-7-96 Minutes e
Key elements of a performance-based approach:
Measurable parameters Objective criteria Flexibility in how to meet performance criteria Failure to meet criteria must not result in unacceptable consequences e
Where practical, the staff supports performance-based strategies in implement ation of the risk-inf ormed decision-making process.
The current proposal supports a limited implementation of performance-based elements pending additional feedback from the pilot applications.
Subcommittee ouestions and corunents Drs.
Apostolakis,
- Kress, and Powers questioned Mr.
Sherry's allowance for higher values of CDF if containment integrity is maintained and offsite dose to the public is limited.
Dr. Powers reiterated earlier concerns regarding bypass events and the possibility of air intrusion and release pathways that may not have been anticipated.
Dr. Apostolak:ts asked what role " time" plays in determining the baseline f rom which small changes (i.e., increases in risk) will be considered.
Industry representatives stated that the baseline should be updated to reflect the analysis at the time of the request for the proposed change.
Dr. Powers asked how the staff would consider total risk with partial PRAs.
The staf f stated that it would use risk partitioning to gain insignts in areas not modeled.
Dr. Apostolakis expressed the view that risk partitioning works less well than placing the burden of proof on the applicant.
The staff stated that it may be necessary to use expert panels to complete the risk assessment.
Dr. Powers questioned the reliability of expert panels.
The staff stated the expert panels could, at times, be better because models do not always reflecc the level of detail needed to make decisions.
Drs. Kress and Apostolakis asked about the staff's plans to handle a group or " package" of licensee requests where some proposed changes increase risk and others reduce risk.
In particular, the they asked how the staff would manage risk trade-of f a to assess the net safety benefit.
The staff reiterated the three options for considering possible increases based on where the subject plant is relative to the guideline.
The staff added that other factors may have bearing on those decisions (e.g.,
a plant on the "watchlist" of problem facilities might have diffir$21ty in gaining approvals).
Drs Kress, Apostolakis, Scale, and Powers expressed the view that
" total" risk should be considered and that increases in risk should be allowed in some situations.
t l
PRA Subcommittee 8-7-96 4' '
Minutes Dr. Apostolakis asked whether the staff would expect licensees to quantify uncertainty.
The staff stated that it would not require quantitative uncertainty analysis.
Sensitivity studies would be acceptable in areas where plant conditions were not modeled.
Dr.
Apostolakis expressed the view that sensitivity studies were subject to abuse and stated that uncertainty should be quantified where modeled.
7 The Subcommittee extensively discussed the NEI/EPRI decision criteria in the PSA Applications Guide.
The staff stated that it had not endorsed the PSA Applications Guide.
Dr. Apostolakis stated that there was some virtue to the NEI/EPRI approach althcugh the partitioning of the three regions may be debatable and the
" fuzziness" of the lines separating the regions need not be exact.
4 Drs. Powers and Apostolakia expressed agreement with the use of CDP and LERF as guidelines for plant-specific applications.
The Subcommittee discussed the lack of performance-based aspects in the proposed SRP sections and associated Regulatory Guide.
Drs.
Seale, Apostolakis, and Kress expressed support for the staff proposal-to use performance-based strategies.
Followun Actions I
l At the conclusion of the Subcommittee meeting, Dr. Apostolakis requested ' that the staff summarize the issues discussed at the 3
Subcommittee meeting to the full Committee during the August 8-10, 1996 ACRS meeting.
Background Material Provided to Subc M ttee for this Meetina 1.
Staf f Requirements Memorandum dated June 11, 1996, from J.
}{oyle, SECY, to John T.
Larkins, ACRS, Subj: Requested ACRS actions regarding meeting with the Commission on May 24, 1996 2.
Staff Requirements Memorandum dated May 15, 1996, from J.
- lloyle, SECY, to J.
- Taylor, EDO, Subj:
Requested actions regarding Commission briefing on PRA Implementation Plan on April 4, 1996 3.
Letter dated July 18, 1996, f rom S. Jackson, Chairman, NRC, to
.T.
Kress, Chairman, ACRS, Subj
" Potential.Use of IPE/IPEEE Results to Compare the Risk of the Current Population of Plants with the Safety Goals" 4.
Letter dated June 6, 1996, from T. Kress, Chairman, ACRS, to S. Jackson, Chairman, NRC, Subj: " Potential Use of IPE/IPEEE Results - to Compare the Risk of the Current Population of Plants with the Safety Goals" t
PRA Subcommittee 8-7 96 Minutes 5.
Letter dated June 3, 1996, from S. Jackson, Chairman, NRC, to '
T. Kress, Chairman, ACRS, Subj Probabilistic Risk Assessment Framework, Pilot Applications, and Next Steps to Expand the Use of PRA in the Regulatory Decision-Making Process 6.
Letter dated April 23, 1996, from T. Kress Chairman, ACRS, to Probabilistic Risk S.
- Jackson, Chairman,
- NRC, Subji Assessment Framework, Pilot Applications, and Next Steps to Expand the Use of Pra in the Regulatory Decision-Making Process" 7.
Memorandum dated July 31, 1996, from M. Markley, ACRS Staff, to G.
Apostolakis, ACRS PRA Subcommittee Chairman, Subj:
Meeting Summary: Briefing of the NRC Chairman on " Issues Related to Probabilistic Risk Assessment (PRA)
Implementation," and attachments 8.
Memorandum dated June 20, 1996, from J.
Taylor, EDO, to S.
Jackson, Chairman, NRC, and Commissioners Rogers and Dicus, NRC, Subj
" Status Update of the Agency-Wide Implementation Plan for Probabilistic Risk Assessment (PRA) (f rom March 1, 4
1996 to May 31, 1996)"
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HQH;:
Additior,al details of this meeting can be obtained from a transcript o this meeting available in the NRC Public d
Document Room, 2120 L Street, N.W.
Washington, D.C.
20006, (202) 634-3274, cr can be purchased from Neal R.
Gross & Co., Inc. Court Reporters and Transcribers, 1323 Rhode Island Avenue, N.W. Washington, D.C. 20005, (202) 234-4433.
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