ML20210H276
| ML20210H276 | |
| Person / Time | |
|---|---|
| Issue date: | 05/27/1997 |
| From: | Apostolakis G Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-3046, NUDOCS 9708130333 | |
| Download: ML20210H276 (7) | |
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fDeF//ilq7 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS MEETING OF THE SUBCOMMITTEE ON PROEABILISTIC RISK ASSESSMENT MEETING MINUTES - JANUARY 28, 1997 ROCKVILLE, MARYLAND INTRODUCTION The ACRS Subcommittee on Probabilistic Risk Assessment (PRA) met on January 28, 1997, at 11545 Rockville Pike, Rockville, MD, in Room T 2B3.
The purpose of this meeting was to continue the Subcom-mittee's review of NRC staff's approach to codify risk-informed, performance-based regulation through the development of Standard Review Plan (SRP) sections and associated Regulatory Guides (RGs).
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 3:30 p.m.
ATTENDEES ACRS G. Apostolakis, Chairman D.
Powers, Member J. Barton, Member W.
Shack, Member I.
Catton, Member M. Markley, ACRS Staff M.
Fontana, Member R.
Sherry, ACRS Fellow T. Kress, Member E. Abbott, Invited Expert D. Miller, Member J.
Garrick, ACNW Member URC Staff M. Cheok, NRR*
R. Jones, NRR M. Cunningham, RES*
T.
King, RES N. Gilles, NRR J. Mitchel, OEDO*
B. Har..iin, RES G.
Parry, NRR W. Hodgas, RES M. Rubin, NRR G.
Holahan, NRR R. Wessman, NRR Industry Reoresentatives B. Bradley, NEI*
A.
Pietrangelo, NEI L. Connor, STS R. Youngblood, Scientech T. Cannon, Arizona Public Service S.
Echols, Winston & Strawn J.
Fulford, NUS*
j S.
Levinson, Framatome Tech.
, // d G /
J. Andre, Westinghouse Ol
- Office of Nuclear Reactor Regulation RES
- Office of Nuclear Regulatory Research OEDO - Office of the Executive Director for Operations NEI
- Nuclear Energy Institute pc
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- Nuclear Utility Services
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i PRA Subcommittee 1/28/97 Minutes A complete list of meeting attendees is in the ACRS Office File, I
1 2
and will be made available upon request.
The presentation slides 4
and handouts used during the meeting are attached to the office copy of these minutes.
l onanina R===rks Dr. George Apostolakis, Chairman of the Subcommittee, convened the i
meeting and stated that the purpose of the meeting was to continue the. Subcommittee's review of the NRC staff's approach to codify risk-informed, performance-based regulation through the development of SRP sections and associated RGs. He noted that the Subcommittee i
had previously met to discuss these matters on october 31, November 1, 21, and 22, 1996, i
Dr. Apostolakis stated that the Subcommittee had received no written comments or requests for time to make oral statements from members of the public.
Presentation by the ACRS Senior Fellew Mr. Rick Sherry, ACRS Senior Fellow, presented an approach to calculate plant-specific risk.
He discussed the individual early f atality frequency (IEFF) based on large, early release frequency (LERF).- Mr. Sherry developed a simplified approach for estimating IEFF risk for comparison with safety goal quantitative health objectives (OHos) for use on a plant-specific basis.
He stated that the approach is generally conservative but not excessively conservative.
He stated that it is more realistic than LERP definition.
His definition includes consideration of both magnitude of radionuclide release and timing of release relative to timing of protective actions (start of evacuation).
Mr. Sherry stated that it is possible to develop more
- detailed, less conservative, functional correlation with release magnitude.
However, one would need to use iodine dose equivalent release to account for impact of other radionuclide spec:.es.
NRC_Staf f Pqual;3tipa Messrs. Gary Holahan, NRR, and Thomas King, RES, led the discussion for the NRC titSf f. fVessra. Robert Jones, NRR, and Mark Cunningham, RES, providad supporting discussion.
Messrs. Mark Rubin and Mike Cheok,_both of NRR, also participated.
Messrs. Holahtn and King provided an overview of the general guidance Regulatory Guide (DG-1061) and associated SRP Chapter 19, "Use of PRA in Plant-Spec'.fic, Risk-Informed Decisionmaking. " They stated that the purpose of these documents was to provide a foundation for efeaff review of risk-informed licensee submittals for plant-specific changt:s to the current licensing basis (CLB).
PRA Subcommittoo
-3 1/28/97 Minutes They noted that the objective of the SRP/RGs was to provide principles and guidance for deterministic and probabilistic analysis and integrated decisionmaking.
The staff noted that the Commission had issued a Staff Requirements Memorandum (SRM) dated January 21, 1997, regarding the following policy issues:
o Performance-based regulation Use of safety goals for plant-specific application e
Risk neutral versus allowable increases in risk e
Acceptable alternatives for inservice inspection (ISI) under e
10 CFR 50.55a Messrs. Holahan and King stated that the Commission had requested a monitoring plan for performance-based approaches to risk-informed initiatives; approved the use of safety goals for plant-specific application but requested review by the legal staf f; approved small increases in risk under certain conditions but requested the staff l
to monitor cumulative changes and to develop a methodology to consider uncertainties; and approved the staff recommendation regarding ISI.
The staff discussed the overall approach for these general guidance documents.
Significant points made during the discussion includes The use of the RG/SRP is voluntary for licensees.
e e
The approach should demonstrate that certain fundamental safety principles are met including: regulatory requirements, defense-in-depth, sufficient safety margin, no significant increases in risk to public health and safety, and utilization of performance-based monitoring and feedback strategies.
The SRP/RGs are intended for changes to the CLB and not for changes made to the f acility and procedures pursuant to 10 CFR 50.59.
Subsidiary objectives of Commission's Safety Goal Policy are used to define benchmark risk levels below which changes are j
considered insignificant
{
a Core damage frequency (CDP): 10-E04/ reactor year Large, early release f requency (LERF) : 10-E05/ reactor year Proposed CLB changes should be risk neutral or decreases, if e
the plant's CDF or LERF is above the benchmark value.
The proposed CLB changes should be made in small increments (less than 10% of benchmark CDF/LERP values) and when within a I
factor of 10 of the benchmark values, the more analysis and management review will be necessary.
The scope of analysis supporting the change should cover all structures, systems, and components (SSCs), operating modes, initiators affected by l
PRA Subcommittee
-4 1/28/97 Minutes the change. The performance must be monitored to help verify key assumptions and check areas of large uncertainty.
Mr.
Mark Cunningham,
- RES, summarized the changes to Draft Regulatory Guide DG-1061, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Current Licensing Basis, a dated January 16,1997.
He noted that the purpose of this guide was to provide general guidance con-cern:,ng one approach that the NRC has determined to be acceptable for analyzing issues associated with proposed changes to a plants' CLB and for assessing the impact of such proposed changes on the risk associated with plant design and operation.
He stated that licensees are expected to address each of the fundamental safety principles listed above in any submittal for risk-informed changes to the CLB.
He stated that licensees can and should identify approaches and methods (whether they are qualitative or quanti-tative, and traditional or probabilistic), data, and criteria that are appropriate for the change being requested and the NRC's need for information to make a decision.
He also discussed a list of expectations associated with these safety principles.
Messrs. Robert Jones, Mark Rubin, and Mike Cheok, all of NRR, provided an overview and discussion of SRP Chapter 19.
They stated that the purpose ot this SRP was to identify the roles and
~
responsibilities of the various organizations in the NRC in the review proceas, provide guidance to the staff for risk-informed reviews of licensee proposals for changes to the plants' CLB, and provide conclusions expected in the staff's evaluation findings.
The SRP was written in parallel with draft guide DG-1061 and reflects the guidance given in DG-1061. It was also founded on the key principles and staf f expectations for risk-informed regulation.
The SRP identifies the types of information that may be used in each activity and provide general guidance on how the information from a PRA can be combined with other pertinent information in the process of making a regulatory decision.
The staf f stated that the guidance in the SRP is an extension of the NRC PRA Policy Statement regarding the use of PRA in regulatory activities.
They noted that it is a key element of the PRA Implementation Plan.
They emphasized that other PRA applications are expected to conform to the guidance in DG-1061 and SRP Chapter 19.
They stated that the industry has pilot applications for:
Risk-informed Technica) Specifications (TS) e Graded quality assurance (GOA)
Inservice testing (IST) e inservice inspection (ISI).
Accordingly, the staff is developing SRP sections and associated regulatory guides for these applications.
The general guidance documents have been developed to allow for the addition of other applications as industry-sponsored initiatives are brought forward.
4 PRA Subcommittee 5-1/28/97 Minutes i
They stated that important elements of the SRP and its appendices include provisions to assures e
The design, construction, and operational practices of the plant being analyzed are expected to be consistent with its CLB.
e Risk evaluations realistically reflect the plant-specific i
design, construction, and operational practices, o
Risk analyses address significant uncertainties.
1 i
The results of the risk analysis will be part of the input to the decision process that evaluates margin in plant capability (both in physical-performance and in redundancy / diversity).
The decision process will use the risk results in a manner which complements traditional engineering approaches and supports the defense-in-depth philosophy and preserves safety margtns.
The staff plans to present three SRP Appendices in addition to the TS,
- GQA, and IST guidance documents during the next PRA Subcommittee meeting scheduled for February 20-21, 1997.
The staff also stated that there are some legal implications that I
need to be considered, and the Commission had requested review by the office of the General Council regarding the allowance for increases in risk in some situations and the legal considerations-(i.e., backfit) for plants that do not meet the guidelines.
Suber---i ttee Ouestions and C-rents In general, the Subcommittee members expressed favorable views of the revised approach taken by the staff regarding the DG-1061 and SRP Chapter 19.
Most-members stated that the SRP/RGs should be j
issued for public comments as soon as practicable.
However, the following concerns were expressed:
i Dr. Apostolakis asked whether the " guidelines" for defense-in-depth l
were actually " elements" or the.y were intended as a " philosophy" of defense-in-depth and safety margins -
The staff said that they i
could be viewed in that way.
Dr. Apostolakis reiterated his i
earlier concern that the risk approach may be constrained if used as guideline.
He expressed the view that defense-in-depth and/or safety margins could be used to defeat risk-informed initiatives if
- implemented as guidelines.
The otaff agreed to consider revising l
DG-1061 to address this matter for both defense-in-depth and safety margins.
l Dr. Catton asked how acceptance criteria for safety margins were considered. The staf f stated that safety margins and uncertainties j
are _ addressed -in.the engineering analysis but noted that margin i
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PRA St$bcommittee
- 1/28/97 Minutes analysis does not fit well with risk analysis.
The staff added that both need to be considered.
Dr. Kress asked about the bases for the plant-specific LERF.
In particu' r, he asked whether larger CDF could be tolerated if LERF is met. 'In addition, other members asked about the need for Level 3 PRA and if a submittal could be used based on the QHOs only.
The staff stated that it would consider these points if provided in a submittal; however, the staff expressed doubt that the guidance would include provisions specifically for this or for all possible combinations of risk arguments.
Drs. Kress and Powers asked how the guidance provides for temporary changes, _ what rates of change are acceptable, and how the time interval could be partiti0ned for an acceptable change.- Dr. Powers also asked if there was any spike in risk which is so high that it i
would be unacce l
values however,ptable.
Tha staff stated that it could establish a the staff emphasized that you cannot get there if the other criteria are met.
Dr. Apostolakis expressed the-view that-the " monitoring program and integrated decisionmaking" could appear overwhelming.
He also stated that integrated decisionmaking should be elevated to that of a key principle because it provides a means by which partial /
incomplete-PRAs may be considered.
The staff agreed to evaluate this suggestion.
Followun Actions The Sub::ommittee requested the staff to address the following items at the February 6-8, 1997 full Committee meeting:
Definition of large, early release frequency and how it applies.on a plant-specific basis Guidelines on the use of defense-in-depth e
e
-Definition. of adequate safety margin and how to maintain aufficient margin e
The use of judgment in licensee expert panels and NRC peer reviews.
The staff agreed to provide updated SRP/RG documents for the full
,ACRS meeting, February 6-8, 1997.
The Subcommittee Chairman noted that a Subcommittee meeting was planned for February 20-21, 1997, to review proposed changes Ln the SRP/RGs for risk-informed TS, GQA, and IST.
3 PRA Subcommittee 1/28/97 Minutes Backaround Material Provided to Subcommittee for this Meeting 1,
Memorandum dated January 21, 1997, f rom A. Thadani, NRR, to J.
- Larkins, ACRS, Subj:
" Transmittal of Revised General Regulatory Guide (DG-1061) and Standard Review Plan (Chapter
- 19) for Risk-Informed Regulation" 2.
SECY-97-009, " Quarterly Status Update for the Probabilistic Risk Assessment (PRA) Implementation Plan," dated January 13, 1997 3.
Draft Staff Requirements Memorandum, Subject SECY-96-218
" Quarterly Status Update for the Probabilistic Risk Assessment (PRA) Implementation Plan, Including a Discussion of Four Emerging Policy Issues Associated with Risk-Informed, i
Performance-Based Regulation," (no date - unofficial) l 4.
Staff Requirements Memorandum, Subj SECY-96-218, " Quarterly Status Update for the Probabilistic Risk Assessment (FRA)
Implementation Plan, Including a Discussion of Four Emerging Policy Issues Associated with Risk-Informed, Performance-Based Regulation," dated October 11, 1996 5.
Letter dated September 6, 1996, from J.
Taylor, EDO, to T.
- Kress, ACRS, Subj
" Risk-Informed, Performance-Based Regulation and Related Matters" 6.
Report dated August 15, 1996,
" Risk-Informed, Performance-Based Regulation and Related Matters" 7.
Staff Requirements Memorandum dated June 11, 1996, from J.
Hoyle, SECY, to John T.
Larkins, ACRS, Subj: Requested ACRS actions regarding meeting with the Commission on May 24, 1996 8.
Staff Requirements Memorandum dated May 15, 1996, from J.
- Hoyle, SECY, to J.
- Taylor, EDO, Subj Requested action:
regarding Commission briefing on PRA Implementation Plan on April 4, 1996 NOTE:
Additionaal details of this meeting can be obtained from a transcript of this meeting available in the NRC Public Document Room, 2120 L Street, N.W.
Washington, D.C.
20006, (202) 634-3274, or 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.