ML20246G247
| ML20246G247 | |
| Person / Time | |
|---|---|
| Issue date: | 01/09/1989 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-2612, NUDOCS 8905150235 | |
| Download: ML20246G247 (34) | |
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SUMMARY
/ MINUTES OF THE ACR$ SUBCOMMITTEE MEETING ON THE RELIABILITY ASSURANCE DECEMBER 12, 1988 BETHESDA, MARYLAND INTRODUCTION The ACRS Subcommittee on Reliability Assurance held a meeting on Monday, December 12, 1988, at 7920 Norfolk Avenue, Bethesda, Maryland to contin-ue the discussion of the Equipment Qualification (EQ)-Risk Scoping Study with special emphasis on the peer-review comments. The entire meeting l
was open to public attendance. Mr. Sam Duraiswamy was the cognizant ACRS Staff Engineer for this meeting. A list of documents submitted to the Subcommittee is included in Attachment A, and a copy of the presen-tation schedule for the meeting is included in Attachment B.
ATTENDEES ,
ACRS: C. P. Siess (Acting Subcommittee Chairman) and C. Michelson Sam Duraiswamy (Cognizant ACRS Staff Engineer)
Principal Speakers NRC: M. Dey, W. Farmer, and T. King SNL: M. Bohn and L. Bustard EXECUTIVE SESSION 1 Drs. Siess, Acting Subcommittee Chairman, convened the meeting at 9:00 a.m. and stated that the purpose of the meeting was to discuss the following with representatives of the Office of Nuclear Regulatory Research (RES) and Sandia National Laboratories (SNL): {
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B Reliability Assurance Minutes December 12, 1988
- Peer-review Comments on the EQ-Risk Scoping Study
- SNL Responses to peer-review comments
- Conclusions / Recommendations of the study
- Anticipated Staff action to implement the recommendations resulting from the study.
He said that the Subcommittee had received neither written comments nor !
requests for time to make oral statements from members of the public.
INTRODUCTION BY THE RES STAFF - DR. M. DEY i
Dr. Dey stated that since'1975 the NRC has fun'ded EQ research to study the methods for' qualifying safety-related electrical equipment and to demonstrate their survivability during and following Desian-Basis Accidents (DBAs) that produce harsh environments. Results of this research are documented in NUREG/CR-4301, " Status Report on Equipment Qualification Issues Research and Resolution." When RES terminated the funding for EQ research by the end of FY 1986, the ACRS, in its February 16, 1986 report to the Congress and the June 11, 1986 report to the Commission, recommended that this research be funded to assess the survivability of electrical equipment under hostile environmental ccnditions resulting from accidents including severe accidents. In response, RES Staff stated that they planned to perform a risk-based prioritization study on EQ in FY 1987 to determine the need for further research in this area. Accordingly, the EQ-Risk Scoping Study was initiated and performed by SNL.
Dr. Dey provided a brief summary of the conclusions of the Scoping Study and major' comments provided by the peer-review panel.
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Reliability Assurance Minutes December 12, 1988 Dr. Dey stated that the Reliability Assurance Subcommittee discussed the EQ-Risk Scoping Study during the meetings on December 16, 1987, and June 14, 1988. It was also discussed by the full Committee during the July 1988 ACRS meeting. During the July ACRS meeting, the full Committee
- decided to defer its comments on this study, pending a detailed. review by the Reliability Assurance Subcommittee of the peer-review comments.
.Dr. Dey requested that the Committee provide its comments and recommen-dations on this matter during its December 1988 meeting.
Mr. Michelson asked whether the EQ research program studied the surviv-ability of equipment under hostile environmental conditions resulting from both DBAs and severe accidents. Dr. Dey responded that the exist-ing E0 rule is limited to DBAs. The research performed was confirmatory in nature to provide bases for the requirements in the EQ rule.
Mr. Michelson commented that it is not mo6e clear in any of the NRC documents what kinds of accidents fall into the DBA category.. Stating that, in his opinion, a fire that burns for an hour in' certain areas and for three hours in some other areas is classified as a DBA. Mr.
Michelson asked whether a fire that burns beyond three hours is classi-fied as a. severe accident. He asked also whether survivability of equipment under harsh environmental conditions created by a fire that burns beyond three hours has been studied. Dr. Dey agreed that fires may lead to severe accidents. However, since environmental conditions '
induced by fires are not included in the existing EQ rule, the EQ-Risk Scoping Study did not look at this issue. He believes that the 1
i fire-related issues are being looked at in some other programs. ,
l Dr. Siess asked why the scope of the EQ-Risk Scoping Study was limited
.to safety-related electrical equipment. Dr. Dey responded that the EQ l rule is limited to safety-related electrical equipment. Also, since the EQ research performed previously was intended to study only those issues
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Reliability Assurance Minutes December 12, 1988 associated with electrical equipment, the scope of the study was limited tc ele < trical equipment.
Mr. Michelson commented that limiting the scope to safety-related electrical equipment may have some problems. He stated that containment recirculating fans, which consists of electrical as well as mechanical components, when subjected to steam and water environment resulting from an accident may not function due to increase in lor. ; from water and steam. He asked whether the survivability of these fans under such an environment has been studied under the EQ program. Mr. Bustard re-sponded that there is an ongoing research at the Idaho National Engi-neerino Laboratory (INEL) related to qualification of mechanical compo-nents. He is not sure whether containment recirculating fans,are included in that program.
Dr. Siess asked whether the It!EL Program includes consideration of severe accidents or just DBAs. Mr. Bustard responded that it is in-tended to look at a whole spectrum of accident conditions. Mr. Farmer, RES, stated that currently the program at INEL is studying mechanical component qualification issues from the DBA point of view. That program is intended specifically to study the ability of the containment iso-lation values and primary coolant pump seals to perform their intended function during DBAs. However, there are plans to study these issues from the severe accident view point. He mentioned that the INEL program does not look at the containment recirculating fans.
GENERAL CONCLUSIONS OF THE EQ-RISK SCOPING STUDY - Mr. L. BUSTARD, SNL Mr. Bustard stated that general conclusions resulting from the study include the following:
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- EQ issues associated with long-term accident equipment operability are not risk significant.
PRAs conclude that core-damage frequency and high-risk significance are substantially dependent on equipment operability during the first few hours to few days after accident initiation. T herefore, less emphasis'should be.placed on demonstrating equipment operabil-ity for a long period of time after initiation of an accident.
- The importance of the accident radiation dose in EQ is overem-phasized.
Current regulations associated with EQ require that all safety-related equipment be qualified to survive a radiation environment created by an instantaneous release of part of the core into the containment at the beginning of the accident. In contrast, PRAs do not calculate substantial in-containment radiation conditions until core melt has occurred. Based on PRA calculations, core melt rarely starts within the first half hour of an accident sequence and may not occur until several hours after accident initiation.
Therefore, the study concludes that current NRC regulations and industry practices overemphasize the EQ risk importance of the accident radiation dose.
- There are selected important system operations not qualified for important accident environments.
Examples include:
- PORV solenoids and bicck valve motor operators during tran-sient induced, and small break LOCA, environments.
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- Low pressure injection equipment after BWR containment venting or rupturing.
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- Analysis included in Draft NUREG-1150 has potentially underesti-mated the importance of selected accident sequences.
Examples include:
Transient induced or small break LOCA PWR sequences.
- BWR transient sequences with loss of suppression pool cooling.
- The importance of plant status instrumentation and post-core damage accident management equipment is difficult to assess using current PRA techniques.
Plant status instrumentation is not well modelled by PRA fault trees. PRAs assume plant status information is reliable and base actuation / failure response on human error. Hence, the risk impor-tance of plant status instrumentation is difficult to quantify.
- When PRA perspectives are combined with existing E0 research perspectives, several historical E0 issues were not found to be risk significant.
Examples include:
- . Simultaneous versus sequential application of accident radia-tion, steam, chemical spray, and pressure conditions.
- Accident dose rate effects.
- Oxygen presence within the test chamber during LOCA simulat-ions.
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Reliability Assurance Minutes December 12, 1988
- When PRA ocrspectives are combined with existing EQ perspectives, several historical EQ issues-have potential risk significance.
Examples include:
- Adequate sealing / protection of safety-related circuits from moisture intrusion / condensation effects.
- Use of air versus nitrogen process gas for solenoid operators.
- Humidity aging effects.
GENERAL RECOMMENDATIONS OF THE SCOPING STUDY - MR. L. BUSTARD, SNL Mr. Bustard discussed briefly the general recommendations resulting from the Scoping Study. -There is a need to:
- Reexamine the EQ regulatory basis.
- Develop further definition of equipment operability time require-ments based on risk perspectives.
- Reexamine whether the requirement that all safety-related equipment be qualified to survive an instantaneous release of the accident radiation dose has adverse impact on risk..
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- Jevelop harsh environment reliability information for selected equipment.
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- Develop guidance regarding operations, maintenance, and inspection l
activities.
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i Reliability Assurance Minutes December 12, 1988
- Develop additional definition of equipment risk importance (e.g.,
plant status equipment, and post-core damage accident management -
equipment).
- Develop improved guidance regarding equipment aging issues.
Stating that some of the conclusions of the study indicate that the existing EQ requirements are deficient in certain areas and too stringent in some other areas, Dr. Siess stated that the Staff should take a look at the current E0 requirements and change them, as necessary, so that they could be applied to equipments that are being replaced at operating plants.
PEER-REVIEW COMMENTS - MR. L. BUSTARD, SNL Mr. Bustard stated that the peer-review panel consists of the following members:
Mr. Kenneth Canady, Duke Power Company Mr. George Sliter, Electric Power Research Institute Mr. Andrew Wolford, INEL Mr. Sal Carfagno, Franklin Research Center.
He stated that the peer-review panel members met twice with representa-tives of SNL to discuss their comments on the' preliminary results and conclusions of the study. In response to their comments, several clarifications and changes have been made to the May 1988 draft report on EQ-Risk study. This draft report was also sent to the peer-review panel for review and comment. Comments provided by the peer-review team fall into the following categories:
- Scope of the study
- Project approach i
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- Importance of accident radiation to equipment operability
- Importance of long duration accident equipment operability
- Importance of equipment accident reliability assessment
- Importance of plant status instrumentation Comments / Recommendations of the peer-review panel on the contents of the May.1988 report and the associated SNL responses are included in Attach-ment C, pages 1-16. Major comments provided by the peer-review panel include the following:
- Prioritization of risk significant equipment operations should not be presented in the report. Rather, each analyzed equip-ment operation should be discussed separately with indications regarding risk importance, subcomponent redundancy, plant variability, etc.
(SNL agreed with this recommendation)
- Conclusions and recommendations of the scoping study should be separately listed in the Executive Summary of the report.
(SNL adopted this recommendation)
- The scope of the study is limited to examining the safety-related electrical equipment and did not examine the mechan-ical equipment such as check valves. Also, the study did not compare-the risk importance of EQ issues to other regulatory issues.
(SNL did not agree with this comment)
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- The report associated with the study should address only the need for further research and should not-discuss issues, such
! as terminal block performance, which have on-going regulatory programs.
l (SNL did not agree with this comment)
- Recommendation for accident reliability data development research does not appear to be within the scope of the. study.
(SNL did not agree with this comment)
- EQ issues highlighted by the study should not automatically be considered applicable to every plant. Additional and more detailed effort would be necessary to assess and substantiate the risk importance of the highlighted issues for a particular plant.
(SNL agreed with this comment)
- If the PRA perspective (regarding time periods during which equipment operability is risk significant) can be confirmed, it could have a major impact on qualification requirements.
More research should be performed to confirm this conclusion.
(SNL agreed that additional work is needed on this issue) l
' Development of accident reliability information is important in determining whether certain EQ issues are risk significant.
(SNL agreed with this comment. However, two of the review team members did not agree with the need for developing accident reliability insights)
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Reliability Assurance Minutes December 12, 1988
- Best estimate environmental conditions and acceptance criteria should be employed during the development of selected accident reliability insights.
(SNL agreed with this comment)
- The peer-review team was in general agreement that current PRA methods do not allow for a reasonable determination of the risk importance for selected plant status equipment. However, some peer-review members felt that it was outside the scope of this study to recommend that PRAs develop better tools for assessing the importance of plant status equipment.
(SNL believe that more definitive assessment of plant status equipment worth would be useful)
Mr. Michelson asked whether the effects of aging on the reliability of equipment are being looked into. Dr. Dey responded that it is being studied for certain important equipment.
Mr. Michelson asked whether they have requalified cartain equipments that are about 10 or 15 years old to make sure that they still qualify.
-Mr. Farmer responsed he does not believe that there have been any requalification tests done on aging equipment. Mr. Bustard stated that utilities have ongoing EQ maintenance programs to periodically check and change the aged equipment.
Stating that aging could be a major contributor to loss of qualification of equipment, Mr. Michelson asked how the aging issue is incorporated into the EQ process. Mr. Bustard responded that artificial aging is already built into the EQ program. In addition, there is a nuclear plant aging research program under way at INEL to look at the aging issues.
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Reliability Assurance Minutes December 12, 1988 Dr. Siess asked whether the peer-review comments and the discussion of these comments will be included in the final report of the EQ-Risk .
1 Scoping Study. Dr. Dey said yes.
Stating that inflattable seals are.being used for personnel access or equipment access in certain plants, Mr. Michelson asked whether any study has been or being done to look at the effects of aging on such seals. Mr. Bustard responded that there is a program under way at SNL to look at the survivability of inflattable seals at elevated temperature conditions.
Mr. Michelson suggested that the Staff /SNL provide a presentation to the
, appropriate Subcommittee of the ACRS on the results of this study at a future date.
Dr. Siess stated that on several occasions he heard that PRAs will be used in prioritizing research programs. However, he has not seen an awful lot of examples of that. He believes that if the EQ-Risk Scoping Study had been performed before the EQ research was begun, the focus of the research might have been different. Mr. Bustard responded that the EQ research helped to determine which EQ issues are risk significant.
He agreed with Dr. Siess that had this study been performed earlier the structure of the EQ research program might have been better.
With regard to one of the peer-review comments related to the accuracy of radiation monitors, Dr. Siess stated that the provisions of Regula-tory Guide 1.97 associated with the accuracy of radiation monitors may be too stringent. We have to decide what we really want to know and how accurately we have to know it, not how accurately we want to know it.
He suggested that the Staff reexamine the provisions of Regulatory Guide 1.97 related to the accuracy of high-radiation monitors.
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Reliability Assurance Minutes December 12, 1988 ANTICIPATED STAFF ACTION TO IMPLEMENT THE RECOMMENDATIONS OF THE EQ-RISK SCOPING STUDY - DR. M. DEY, RES Dr. Dey stated-that EQ-Risk Scoping Study has:
- Provided risk significance of EQ research issues.
- Determined that several EQ research issues in NUREG/CR-4301 lack risk significance.
- Concluded that v - new generic issues need to be extanined.
- Provided useful framework for:
- Analyzing EQ requirements and determ'ning items for focus during EQ inspection.
- Examining the possible need for equipment operations during events not included in the basis of EQ rule (10 CFR 50.49).
- A risk-based approach to EQ.
Dr. Dey stated that the results of the study will be utilized towards:
- Reviewing Individual Plant Examination submittals.
- Implementing the Severe Accident Policy statement for future reactors. I Mr. Michelson stated,that although several equipments share the same environment, some of them are not qualified for the severe accident environment. There is a possibility that these unqualified equipments may create some unwanted actions under a harsh environment causing systems interactions problems. He does not believe that existing PRAs
4 Reliability Assurance Minutes December 12, 1988 treat unwanted actions created by certain equipment well. He asked whether this issue has been given consideration. Dr. Dey responded that the EQ-Risk Scoping Study used the information from the existing PRAs.
SNL did not try to develop new PRA models. The Staff does not claim that the systems interactions problem has been resolved.
Mr. Michelson suggested that it would be helpful if the EQ Scoping Study report included clear statements as to what was considered in the study and what else remains to be considered. Mr. Bustard responded that in the revised report, they have included such information.
1 With reference to the statement made by Dr. Dey that EQ-Risk Scoping l Study has provided framework for determining items for focus during EQ f inspections, Dr. Siess stated that the inspections are performed in f accordance with the existing regulations. If they want to change the focus of inspections, the regulations have to be changed. He asked whether they plan to make changes to the existing regulations. Dr. Dey responded that there is no plan at present to change the regulations.
They plan to provide specific recommendations to NRR and regions for consideration and possible implementation.
Stating that Regulatory Guide 1.89 also provides guidance for qualifica-tion of electrical equipment, Dr. Siess asked whether they plan to change this Guide if it was found that certain things should be changed as a result of the scoping study. Dr. Dey responded that they do not plan to change this Guide at this time. They may change it to provide guidance for future plants.
Dr. Siess commented that during the next several years, operating plants '
may replace an awful lot of equipment. If the existing EQ requirements are deficient or too stringent, they should be modified and applied to qualify this replacement equipment. The Staff's intention to change l
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Reliability Assurance Minutes December 12, 1988 i
i the existing EQ requirements only for application to future reactors l does not make sense.
In response to a question from Dr. Siess, Dr. Dey stated that based on the results of the study, they have concluded that additional EQ re-search is not necessary.
Dr. Siess commented that it would have been helpful to have had this sort of scoping study performed before establishing the requirements for
- E0. He reiterated that had a risk-based scoping study been performed before the EQ research program was begun, rather than after it was completed, the nature and scope of the research program might have been different and presumably better.
Stating that the Staff and the ACRS are in the process of reviewing advanced reactor designs, such as Advanced Boiling Water Reactor, Westinghouse Advanced Pressurized Water Reactor, etc., Mr. Michelson asked when the Staff is going to establish EQ requirements for such designs.
Dr. Siess stated that NRR had a retreat on October 3-4, 1988 to consider means to incorporate all the lessons learned from the severe accident studies into the future evolutionary LWRs.
Mr. King, RES, stated that they are in the process of developing a rule to implement the severe accident policy for future LWRs. They expect to issue this rule well before issuing the first final design approval.
Also, they plan'to discuss this rule with the appropriate ACRS Subcom-mittee during March 1989.
In response to a question from Dr. Siess, Mr. King stated that all future evolutionary LWRs will have containments.
e Reliability Assurance Minutes December 12, 1988 SUBCOMMITTEE REMARKS l
l Dr. Siess stated he believes that the peer-review process has contri-buted to the credibility of the conclusions of the study and quality of l
the ~ final report.
The. Subcommittee decided to prepare a draft report, including comments and recommendations;on the EQ-Risk Scoping Study and also on the anticipated Staff's plans to implement the recommendations of the study, and submit it to the full Committee for consideration and approval.
during the December 1988 ACRS meeting.
Dr. Siess thanked all participants and' adjourned the meeting at 3:15 p.m. -
NOTE: Additional meeting details 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) 634-3273, or can be purchased from Heritage Reporting Corporation,1220 L Street, N.W., Suite 600, Washington, D.C. 20005,(202) 628-4888, i
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LIST OF DOCUMENTS SUBMITTED TO THE RELIABILITY ASSURANCE SUBCOMMITTEE DECEMBER 12, 1988 MEETING
- 1. Presentation Schedule 2.- Executive Summary of the Equipment Qualification-Risk Scoping .
Study.
- 3. Conclusions / Recommendations of the Scoping Study.
- 4. Peer-Review Comments.
- 5. Equipment Qualification Risk Scoping Study: Discussion of Peer-Review Comments.
- 6. Minutes of the December 16, 1987 and June 14, 1988 Reliability Assurance Subcommittee meetings.
- 7. Portion of the Minutes of the_339th, July 14-16, 1988, ACRS meet- i
'ing.
- 8. Presentation Materials Provided during the meeting.
1 ATTACHMENT A 4 L
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, REVISED
, 12/8/88 PRESENTATION SCHEDULE ACRS SUBCOMMITTEE MEETING ON i' RELIABILITY ASSURANCE DECEMBER 12, 1988 ROOM P-114, 7920 NORFOLK AVENUE BETHESDA, MARYLAND ACRS CONTACT: Sam Duraiswamy 301-492-9522 ,
NOTE:
- Presentation Time should not exceed 50% of the Total Time allocated for a specific item. The remaining 50% of the time is reserved for the Subcommittee questions and answers by the Staff or its contractors.
- Number of copies of the presentation materials to be submitted to the Subcommittee: 25 copies.
4 TOTAL PRESENTATION ITEM PRESENTER TIME ACTUAL' TIME
- 1. EXECUTIVE SESSION --
15 mins 9:00 - 9:15 am
- 2. INTRODUCTION BY THE RES 15 mins 9:15 - 9:30 am STAFF Moni Dey)
(NRC/RES
- 3. PEER-REVIEW COMMENTS ON Larry Bustard 60 mins 9:30 - 10:30 am THE EQUIPMENT QUALIFICA- (SNL)
TION - RISK SCOPING STUDY l *** BREAK *** 15 mins 10:30 - 10:45 am
- 4. RESPONSE TO PEER-REVIEW Larry Bustard 45 mins 10:45 - 11:30 am COMMENTS (SNL)
- 5. CONCLUSIONS /RECOMMENDA- 60 mins 11:30 - 12:30 pm TIONS OF THE STUDY AND Moni Dey)
(NRC/RES ANTICIPATED STAFF ACTION
- 6. SUBCOMMITTEE REMARKS -- 15 mins 12:30 - 12:45 pm
- ADJ0 URN **** 12:45 pm l .
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ATTACHMENT B 1
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e PEER REVIEW COMMENTS: PROJECT SCOPE Recommendations to establish the risk importance of plant status equipment is outside the scope of this study (S.C.).
i Recommendations to assess accident equipment reliabilities is outside the scope of this study (A.W.).
Study conclusions should be focussed towards future research activities, not regulatory concerns (K.C.).
Project charter should drop goal of assessing EQ risk uncertainty (A.W.).
Report should discuss historical basis and conservatism of EQ process (G.S.)
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SANDIA RESPONSE: PROJECT SCOPE *
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EQ issue importance for plant status equipment would be better established with knowledge of equipment risk importance.
Study charter did not differentiate between research and regulatory concerns.
Study charter included NUREG/CR-4301 issues. These include the reliability issue.
In the absence of accident reliability information, rigorous quantitative assessment of EQ risk uncertainty is not possible.
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i PEER REVIEW COMMENTS: PROJECT APPROACH Pros:
I Project team appears to be doing an excellent job on a difficult, and long overdue, research topic (G.S.).
Study is sufficiently rigorous to eliminate equipment / issues from further consideration (K.C.).
Approach is adequate given the scoping nature of the study (G.S.).
Equipment operations are sufficiently complete for this scoping study (G.S.).
Coverage of potentially risk significant EQ issues was abundantly thorough (G.S.)
The study appears to have identified all risk significant electrical equipment that could be subject to a harsh environment (K.C.).
Approach is thorough and should identify the majority of environmentally vulnerable and qualification deficient equipment under severe
< accident conditions (A.W.).
Approach is' adequate for screening purposes (A.W.).
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I PEER REVIEW COMMENTS: PROJECT APPROACH Cons:
Scoping studies that employ bounding .
assumptions are not sufficiently rigorous to identify generic conclusions or testing requirements; plant specific analysis is required (K.C.).
Study should emphasize risk rather than core damage frequency as a parameter of interest (K.C.,
A.W.)
List of risk significant equipment operatidns may not be complete because of inadequacies in PRA methodology (S.C.).
Approach does not provide the consistent technical and physical basis necessary to prioritize issues / equipment (A.W.).
Work provides no basis for ranking or comparison to other issues outside its scope (e.g. for qualification of mechanical equipment under dynamic loads) (A.W.)
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PEER REVIEW COMMENTS: PROJECT APPROACH Cons (Continued):
Future PRA improvements (modelling of accident management and age-dependent system performance) may lead to the identification of important harsh environments not considered in current PRAs (A.W.).
More rigorous mathematical formalism is desirable for assessing EQ issue risk importance (A.W.).
Iterative PRA and EQ approach for identifying candidate equipment operations is more difficult to document and less reproducible than an independent development approach (A.W.).
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SANDIA RESPONSE: PROJECT APPROACH Agree that additional effort would be necessary to assess risk importance of highlighted issues for a particular plant. Cautionary remarks added to l report.
Recent IPE Generic Letter justifies emphasis on core damage frequency as well as risk.
Agree that bounding calculations do not provide a
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rigorous prioritization basis. Report format reflects '
this conclusion.
Lack of accident reliability databases does not support development of rigorous mathematical formalism for this effort.
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PEER REVIEW COMMENTS: EQ issues associated with long term accident equipment operability are not risk I significant.
Pros:
Agreement (K.C.).
The most interesting observation of the study.....lf the validity of this observation can be confirmed,it could have a major impact on qualification requirements (S.C.).
Cons:
Currently not willing to accept PRA short term accident risk perspective (S.C.).
PRAs short term accident operability perspective deserves more attention and clarification in the report (G.S.).
PRA perspective is historical, not fundamental. UK and France are beginning to apply PRA for accident periods of one month to one year (G.S.). .
EQ's long duration accident perspective helps justify PRAs short term perspective (A.W.).
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4 SANDIA RESPONSE: LONG TERM ACCIDENT EQUIPMENT OPERABILITY ,
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i Agree that study's conclusions could have major Impact on EQ requirements.
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Suggest additional research for further development of consensus support for study's conclusion, investigate post-accident management f strategies. l l
Investigate risk importance of plant status equipment.
Disagree that current "long term" EQpractice "
Lustifies PRA "short term" perspective.
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I PEER REVIEW COMMENTS: The importance of the~
accident radiation dose in EQ is overemphasized.
Pros:
The conclusion is well supported by the techniques employed in the study (A.W.)
We agree that elimination of the need for the :
" instantaneous radiation release" EQ requirement
...might... reduce risk (K.C.).
Suggest identification of a more realistic EQ source term to remove distortions in qualification testing (S.C.). -
Agreement (G.S.).
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PEER REVIEW COMMENTS: The importance of equipment accident reliability assessment.
Pros:
Accident reliability information may be usefulin assessing the risk significance of remaining issues (K.C.).
PRA use of normal operation reliabilities is not valid (S.C.).
A pattern of lower reliability in harsh environments is consistent with my EQ experiences (S.C.).
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Accident reliability development should be based on best-estimate operating parameters (G.S.)
Type tests cannot characterize uncertainties (issues) inherent in simulations employed (G.S.).
There is not an extensive accident reliability data base (S.C. and G.S.)
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PEER REVIEW COMMENTS: The importance of equipment accident reliability assessment.
Cons:
The scoping study has not established the need for accident reliability information (S.C.).
Of greater importance is the uncertainty associated with accelerated aging techniques....(S.C.).
Other reliability data development activities could be shown to be of equal or greater risk significance
( A.W.) .
Recommendation is not within the scope of the study (A.W.)
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SANDIA RESPONSE: ACCIDENT RELIABILITY ASSESSMENT Current PRAs have potentially underestimated importance of selected sequences via their use of normal operation reliabilities to describe accident equipment behavior.
. Lack of selected accident reliability assessment creates several order of magnitude uncertainty for the contribution of selected sequences to core damage frequency.
Potentially impacts choice of accident management strategies. !
Creates uncertainty regarding base case core damage frequency.
Selected accident reliability insights would support the continued use of a risk-based regulatory approach.
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PEER REVIEW COMMENTS: The importance of plant instrumentation. -
Recognized difficulty of assessing risk importance '
of plant status equipment via PRA methods (G.S.)
Study overemphasized the importance of high '
range radiation monitors and steam generator level detectors (K.C., G.S.).
Emergency response decisions rely on a variety of l Indicators; evacuation and sheltering decisions 1 oftern made long before r'adiation monitors would detect core damage (K.C.).
Feed and bleed reliabilities employed in the report are overly conservative leading to an l overestimation of the importance of the steam generator level detectors (K.C.).
C-13
/
s s'
PEER REVIEW COMMENTS: The importance of plant ,
instrumentation (Continued), ,
Some plants allow feed and bleed via the SRVs as well as the PORVs; this generates less need for g steam generator level detection (K.C ,.
Recommendations to establish the risk importance 3
of plant status equipment is outside the scope of this study (S.C.)
ci Recommendation to establish the risk iniportance of plant status equipment is unsupported since the study did not bound its potential risk impact.
C-f4
0 - s SANDIA RESPONSE: Plant Status Instrumentation an Additional discussions regarding high range radiation monitors and steam generator level detectors were added to the report.
Plant status instrumentation may be desired during post-core damage conditions.
Operability after extensive multiple hydrogen burns is questionable.
Recommend that accident management strategy programs assess which instrumentation is truly I
needed via risk analysis.
3 C-6 .
e.e.4
,s 4
SANDIA RESPONSE: Plant Status Instrumentation Additional discussions regarding high range radiation monitors and steam generator level detectors were added to the report.
Plant status instrumentation may be desired during post-core damage conditions.
Operability after extensive multiple hydrogen burns is questionable.
Recommend that accident management strategy programs assess which instrumentation is truly needed via risk analysis.
C-/6
..