ML20236T667
| ML20236T667 | |
| Person / Time | |
|---|---|
| Issue date: | 10/08/1987 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-2525, NUDOCS 8712020002 | |
| Download: ML20236T667 (24) | |
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I Id: Li L Li up jg DATE ISSUED: October 8,1987 l
SUMMARY
/ MINUTES ON THE l ACRS SUBCOMMITTEE MEETING 0N EXTREME EXTERNAL PHENOMENA <
SEPTEMBER 29, 1987 I l
The ACRS Subcommittee on Extreme External Phenornena met on September 29, j 1987 at 1717 H Street NW., Washington, D.C. The purpose of this meeting was to: 1. Review the NRC Seismic Design Margins Program methodology j l
and the application to Maine Yankee. 2. Discuss.the EPRI seismic l design margins programs and compare them with the NRC/ Maine Yankee 1
methodology 3. Access the applicability of the NRC Seismic Design l l
l Margins methodology to the treatment of seismic events implementation of the Severe Accident Policy j 1
The discussions began at 9:00 a.m. and were concluded at about 6:30 p.m.
and were ennducted in open session. The principle attendees were as !
follows:
ACRS NRC l C. P. Siess, Acting Subcommittee Chairman A. Murphy, RES l C. W. Wylie, Member D. Guzy, RES l R. Savio, ACRS Staff ACRS Consultants:
G. Cummings R. Murry 8712O20002 871008 D. Moore
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M. Ravindra R. Budnitz l Maine Yankee Power Company F. Coffman, RES D. Whittier G. Cumings W. Henries J. Chen, RES S. Evans L. Reiter, NRR W. Metevia G. Bagchi, NRR EPRI p IGNATED ORIGIIAL
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N .- MINUTES / Extreme External 2 Phenomena M2g., Sept. 29, 1987 The agenda for these discussions is included as Attachment A.
Highlights
- 1. Mr. Murphy presented a summary of the work being carried out under the NRC's Seismic Safety Research Program. This program is designed to better quantify (i.e., to improve the methodology and to assess the uncertainties) seismic hazard, the seismic design l margins for operating plants, and the seismic margins produced by current NRC and Industry practices. This program is described in detail in NUREG-1147, Rev. 1 (May 1987). The structure of this program and its relationship to NRC regulatory needs and to related programs being carried on outside of the NRC is displayed on page 1 !
I of Attachment B. Research in NRC's Seismic Safety Research Program l
l and can be grouped into four areas.
o Earth Sciences - This work is designed to address issues that contribute to the uncertainty in seismic hazard assessment, especially for nuclear facilities located in the Eastern and Central United. States. The principal issues are related to the uncertainties in establishing seismic source zones, l propagation of seismic energy, and the site-specific ground l
motion response, including soil failure. The earth sciences l research program consists of three elements: (1) regional projects that address the uncertainty in seismic source zone configurationsandseismicenergypropagation;(2) topical projects that deal with developing site-specific spectra, strong ground-motion models, and soil failure models; and (3)
r ,. MINUTES /Extrame External' 3 Phenomena Mtg., Sept. 29, 1987 probabilistic projects that deal with techniques to handle the uncertainties.
i o Seismic Margins - This work is designed to develop a methodology for existing nuclear power plants. (Inthis
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context, margin is defined as the capability.of a plant to sustain an earthquake larger than its safe shutdown 1
earthquake.) The NPC Seismic Design Margins Program is devel-oping review procedures and screening guidelines based on the ;
results of previous and ongoing research (for, example, I probabilistic risk assessments and piping, component,.and building dynamic tests) to evaluate the seismic margin of operating nuclear plants.
l !
l o Fragilities and Response - This work is designed to develop I capabilities to better predict the behavior of structures, I systems, and components subjected to seismic loads causing )
inelastic or nonlinear response. This research, if ,
successful, will reduce the large uncertainties in the i
fragility or failure data base used in seismic margins studies. Response and/or fragility data will:be obtained on structures, components, piping, and dams and embankments.
o Validation - This work is designed to validate experimentally the calculational methods used in probabilistic risk assessments, and seismic margins studies. .The research efforts involve cooperative research programs using large i
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l
' MINUTES / Extreme External 4
.- .- Phenomena Mtg. Sept. 29, 1987
.- . foreign test facilities in order to maximize the return from ;
available resources. As such, cooperative efforts with the- ;
Electric Power Resear'ch Institute with West Germany and Japan ]
i have been established.
)
'The shear wall and model building testing being conducted at !
LANL was discussed. Dr. Siess stated that this work was not j well focused and that the information sought could be better obtained by the study of experiences with structures which had j been subjected to damaging earthquakes. l I
l l !
l 2. D. Guzy discussed the scope of and the regulatory uses of the NRC Seismic Design Margins Program. The program was initiated in 1984 1
with the organization of some existing and some new research programs into a single plan coordinated by a NRR/RES working force. I The program is for the most part directed at Eastern U.S. seismic design issues. NRC has been utilizing expert panels to review the progress of the work and contractors to perform the actual work.
The personnel employed for these functions are listed on pages 2 to l 4 of Attachment B. A methodology (described in NUREG/CR-4334, August 1985 and NUREG/CR-4482, March 1986) has been developed that uses what has been learned from the current group of seismic PRA's, from actual earthquake experience.with' industrial facilities, and from the work of the Seismic Qualification Utilities Group (USI A-46),toevaluateseismicmargins. Lawrence Livermore National Laboratory (LLNL) was NRC's principal contractor. The method puts emphasis on using experience and seismic design insights to assure E-_-_--__- - - - - - - - - _ - - - - -z
,. ,. MINUTES / Extreme External 5 1 Phenomena Mtg.. Sept. 29, 1987 !
that the structures and equipment'have adequate seismic margin.
The procedure has been applied on the Maine Yankee plant (CE).in a cooperative NRC-LLNL-Utility effort. The Maine Yankee study took j approximately 9 months to complete. EPRI is also developing a methodology that is similar in many ways to what NRC is using and has a? plied this methodology to the Catawba (W) plant. NRC has cooperated with EPRI in comparing the NRC and EPRI methodologies-and will issue NUREG reperts on this effort in the near future.
The NRC and EPRI are currently discussing a joint NRC/EPRI effort on the analysis of a BWR. The Hatch Unit 1 plant is likely to be chosen for this study.
- 3. The NRC's methodology involves the use of the "HCLPF" (high confi-dence, low probability of failure) concept. Fragilities are j developed for a preselected response spectrum. Seismic hazard l curves are not directly utilized in this method. In practice, the l
g-value/ response spectrum that is used would be that judged to be ;
I appropriate for the site. This method involves two plant walkdowns l
and a systems analyses that is used to gain risk prospective on the seismic performance of structures and equipment. The goal is to identify seismic margins and is focused on "high confidence", j rather than "best estimate" analysis. Th'e methodology does not )
i lead directly to the quantification of core melt frequency (CMF) or j risk. Some insights as to the level of seismic CMF and risk can be j obtained from judgment and the insights obtained 'from existing PRAs. The methodology is outlined on page 5 of Attachment B.
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tn o ,- MINUTES / Extreme-External _. :6.
Phenomena Mtg., Sept'. 29, 1987 4 Mr. Murry, Mr. Moore,_and Mr.:Ravindra described the'. application of, !
the.NRC's' Seismic Design Margins-Program methodology to the Maine Yankee plant. kprojectteamwasorganizedandtechniques:
recommended in the.NRC's metho'dology were' applied to the Maine. 'j Yankee plant. A NUREG/CR-0098-(Newmark) median-response spectrum-
.I anchored at 0.3g was used. The selection of'O.3 9 was to a large' J
l extent judgemental. Fragility data.is relatively well defined to about that level. :It was'also: expected that'most plant. structure's O and components could be judge'd to be adequately designed (i.e,-to the HCLPF criteria) to that levellin a preliminary. screening. No j walkdown inspections' wereLconducted inside containment because of. j operational and scheduling considerations, and aging was not .
considered in evaluating fragility.. The plant seismic margins were l
evaluated using the 0.39 HCLPF and a decision was made by. Maine Yankee to perform some plant modifications: A list of the equipment / structures which were modified is' given on page 6 ~of Attachment B. Themodifiedplantwasjudgedtobequalified(via the HCLPF criteria) to a median NUREG-0098 response. spectrum greater than 0.3g for accident scenarios not-involving a LOCA.. For 5 scenarios involving a LOCA (and thus a dependence on the Refueling Water Storage Tank) the plant was judged.to be qualified-to a HELPF.
of 0.279 after the plant modifications were performed.~ ;
i l 5. The' Maine Yankee analyses'was discussed in some detail. .Two -
important accident sequences were identified. Both are initiated by a. seismically induced loss of offsite power (LOSP).which was' assumed to. occur at the review (0.3g). earthquake level.- In one t ,
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'i MINUTES / Extreme External -7 .
- /. < Phenomena Mtg.. Sept. 29, 1987 sequence a'small' loss-of-coolant accident (LOCA of 3/8 in. to 2. in.
)
diameterequivalentarea)occursbecauseofseismicallyinduced
-pipe breakage. HCLPF capacities for components which might cause other' types of small LOCAs-(pump seal. or. power-operated relief - !
)
valve LOCAs) were sufficiently high so-.they could be: screened out. /
The other accident sequence assumed no.small LOCA.
l The small'LOCA accident' sequence involved seismic failures only and -
resulted in a plant (in the as~ fo'und' condition) HCLPF.of 0.21g.
Plausible' arguments exist to support the premise.that a small LOCA.
]
would not occur with'the. response' spectrum considered. However, as previously stated (see Highlight 4) the. team involved in the review.
could not get inside the' Maine Yankee containment and were not able '
to inspect the small primary system piping. For this reason, they were not able to exclude the pssibility of the failure of small
, piping. If they had, this sequence may not have been considered l
and the plant HCLPF would be.above.0.30g. By the same set of l
circumstances, multiple failures of small pipes could not be excluded and a potential could exist for LOCA larger than 2 in.
diameter equivalent area..
l The small LOCA' accident sequence was composed of three single cut sets with the dominant contributor being failure of the Refueling Water Storage Tank (RWST)'which had an "as found" HCLPF of 0.219 .
Other single cut sets in the sequence had HCLPF's greater than l 0.30g. .
1
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MINUTES / Extreme External 8 Phenomena Mtg.. Sept. 29, 1987 1 The'second accident sequence was a LOSP.with.no small LOCA, and involved no single set but a number of double sets, some combining seismic and nonseismic (random,' test and maintenance, human error) -
failures. The most important double set is the Demineralized Water- )
Storage Tank (DWST, HCLPF = 0.179) and the Circulating Water Pump House (HCLPF = 0.30g). .;
Nonseismic failures were found not be important contributors. The. ;
system degradation resulting from these failures made no contribution to the overall plant level HCLPF capacity. The most- -;
important nonseismic failure found was a common cause failure 'of
( i the Auxiliary Feedwater System, caused by steam binding.(median unavailability per demand of 1.2 x 10~4).
l It should be noted that during the review process, important components were'found for which a low HCLPF would result or ;
insufficient data was available to determine the HCLPF. These were j the lead-antimony station batteries, the station service transformers, a block wall near HVAC equipment, parts of air conditioning heat exchangers, for equipment areas and anchorage of j the diesel generator day tanks. To reduce the uncertainty in establishing the capacity of this equipment, components are being replaced or upgraded.
Mr. Murry, Mr. Moore, and Mr Ravindra indicated that the Maine Yankee seismic margins review provided some insights applicable to future reviews. The event / fault tree methods used provided a l
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MINUTES / Extreme External 9 t .- Phenomena Mtg.. Sept. 29, 1987
- complete description of dominant contributors and considered all important systems. The fragility screening table (as described in l
NUREG/CR-4334) needs to be strengthened and better guidance needs i to be developed on how to select a review-level earthquake. In '
addition, more guidance is needed on how to use and characterize component capacity and how to combine seismic and nonseismic failures.
An additional insight gained was that the systems analysis effort l should begin as early as possible so that this information can be )
I I
factored into component screening and plan walkdowns can be done '
efficiently. Information in the plant Final Safety Analysis Report can be effectively used for this effort. Plant walkdowns need to l
be carefully planned, taking into account auxiliary systems such as '
the HVAC and actuation / control system, as well as important systems and components identified in the systems analysis. These walkdowns
! are essential to successful margin reviews. Specifically, they 1 1 permit accurate data collection and allow identification of potential low capacity components.
l It was also noted that more guidance needs to be developed on the consideration of the seismically initiated small LOCA. This 1
initiating event turned out to e particularly important at Maine Yankee. It may be impossible to review and inspect all of the small primary pressure boundary piping, and other screening methods need to be developed, e.g., inspection of similar piping outside of containment.
' MINUTES / Extreme External 10 Phenomena Mtg.. Sept.. 29, 1987 Finally, Mr. Murry, Mr. Moore and Mr. Ravindra noted that there is '
i a question about maintenance of hot' shutdown for a specified period.
of time after an earthquake, e.g., 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. . The current methodology addressed the attainment of hot shutdown but not :
necessarily its maintenance. Review of previous seismic PRAs ;
l indicated that once hot shutdown'is attained, the probability of maintaining it is large. Therefore, this issue may be of less importance. -
The Maine Yankee analysis is discussed in detail in NUREG/CR 4826, q l
l Volumes 1 to 3. i 1
- 6. Mr. D. Whittier of the Maine Yankee Power Company discussed Maine l Yankee's participation in his study. Mr. Whittier stated that the j
NRC-sponsored study was well planned and well executed. He also ;
stated that the study confirmed that the plant was inherently earthquake resistant. Mr. Whittier stated that Maine-Yankee sup- ;
1 ports the use of earthquake experience data and the general ap-proach used in the Maine Yankee study in future seismic design margin studies.
l
- 7. Mr. R. Budnitz described the activity of the NRC's Maine Yankee Trial Review Peer Review Group (PRG). The PRG contained persons from industry and from SNL (see page 7, Attachment B). The PRG-objective was to review and assure the adequacy of the application.
1, of the NRC's seismic margins methodology to Main Yankee. The PRG l
l concluded that the Maine Yankee application met this criteria. -The
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. V 'l. % y c MINUTES /Extrems ExternG1 11- , i f i.\
Phenomena Mtg. Sept. 29, 1987 <
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. . s PRG's findings'and comments are summarized on pages 8 to M of f ,
Attachment B.
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- 8. Mr. R. Kennedy described the EPRI methodology. Mr. R. Buc'nitz S discussed comparison of this EPRI methodology to the NRC methodolo-gy. The EPRI. methodology was based on the NRC work.. Mr. Kennedy /
indicated that the EPRI methodology used simplified pro: bres s
(adding conservatism where necessary) to facilitate the a e of the ! I methodology. The EPRI procedures are generally more determirdstic.
and are less dependent on expert jud,ement. t The (Yydems analyses methods are " success" orientedIs compared to th " fail-( I ure" oriented system analyses methods used in the NRC procedures.
1
? r' Neither the NRC or the EPRI methodology leads to t cuantification l
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l~ of seismic risk. NRC and EPRI believe that with the appropriate ( h i t .;
j selection of the HCLDF can assurj;that seismic risk A is M* ceptably g j low. \, \
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- 9. Mr. F. Coffman indicated thtt the NRC ir[thrrentif//nipyng P r, \ '(
,(
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l methodologies for findus p icmic risy r.utiliers for use %1 the 1 3l:
Severe Accident Policy N DtP) implementation. A dec'isio as not- 'r' '
yet been made as to what' approaches will be acceptable to the NRC. U y <
- * * $ *,r * ******
f+ f NOTE: A transcript of the meeting is available in the NRC Public' '
i Document Room, 17*.7 H Street, NW, Washington, D.C. or can' be purchased from Heritage Reporting Corporation. 1220 L Street, j NW., Washington, D N. 20005, Telephone: (202)628-4888. All documents listed in Attachment D are available in the ACRS g'
/p files.
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Revised: 9/16/87 o
.g Proposed Agenda for the V September 29, 1987 Meeting of the ACRS Subcommittee on g, l
. Extreme External Phenomena s Nrpose: Th objectives of these Subcommittee discussions'are to:
(l') Review the NRC Seismic Design Margins frogram and the application of the methodology to Maine Yankee.
-(2) Discuss the EPRI seismic margins methodology and
/ compare thea with the NRC/ Maine Yankee methodology, i
(3) Actess the_ applicability of the NRC Seismic Margin methodology to the treatment of seismic events
,' j
, implementation of the Severe Accident Policy.
l l g ;s
[T 1. Executive Session - C. P. Siess 15 min 9:00 - 9:15 am
- 2. Summary of' Seismic Safety Research 45 min 9:15 - 10:00 am i
Program - Description of programs, l
accomplishments, and current status -
3 /, , A. Murphy l
1
' 3. , Discussion of NRC Seismic Design
.,j i y Margins Programs i ,la ) Status'of the Seismic Design 30 min 10:00 - 10:30 am l l
Margins Program and discussion i of the Methodology - D. Guzy l
! *** BREAK *** 15 min 10:30 - 10:45 am (b) Application of Seismic Margins 2 hrs 10:45 - 12:45 am Methodology to Maine Yankee . !
/ Ii R.Murry(LLNL),D. Moore (EI), !
f a and M. K. Ravidra (EQI) l t'
I *** LUNCH *** 60 min 12:45 - 1:45 pm i (c) Report of the Maine Yankee 15 min 1:45 - 2:00 pm A (l ,
Peer Review Group - R. Budnitz !
l (d) Future pians - D. Guzy- 15 min 2:00 - 2:15 pm !
f (e) Coments by Maine Yankee Power 15 min- 2:15 - 2:30 pm l
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EEP Proposed Agenda ' September 29, 1987 .1
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4 < Discussion of EPRI Seismic Margins j Methodology ,g -
W (a) Description of EPRI. Methodology. 45 min M- 3:15 pm-
- R. P. Kennedy n *** BREAK *** 15 min. 3:15: 3:30 pm 7
(b) Discussion 'of EPRI Methodology 30 min. 3i30' '4:00 pm'
, > and Comparison with the.NRC--
methodology - R..Budnitz W
- 5. Application of Existing Seismic 60 Ar 4:00 - 5:00 pm '
4 Margins Evaluation Methodologies. ]
to the Implementation of the' Severe .1 Accident Policy - To-be designated j by T. Speis 1
- 6. Summary, Conclusions, and Future 15.. mi n' 5:00 5:30 pm ,
Subcommittee Actions - C. P. Siess I j
ACRS Staff
Contact:
Dr. Richard Savio.
202-634-3267(Office) 301-757-6276'(Home) f i
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- Gather information on on systems and sort , ; . . /.l -* the plant. Determine which I l
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ion 3 mmponents have
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- l. . *.* *:. * .* . A level. Pot.sibly identify plant-unique fe.atures.
.- First plant walkdown:
. Concentrate on identification of problems.
. '4 Emphasize systems interaction. Confirm
/.',,.- applicability of screening tools. Complete identification of plant-unique features.
o KEY: Task is performed by: . : . . ..l: f,* Revision of systems C ' ' * * *
- relationships established
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6 Collect specific data (size and other i i physical characteristics) of components j requiring detailed analysis. !
o Determine minimal ,.**.*.**t.*.
. Finalize HCLPF value for cut sets for end-
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2 PEER REVIEW GROUP MEMBERS -
i Robert J. Budnitz (chair) Future Resources Associates, Inc.
l Michael P. Bohn Sandia National Laboratories l
l John W. Reed Jack R. Benjamin & Associates, Inc.
l.
1 James Thomas Duke Power Ct.,mpany i
, Loring A. Wyllie, Jr. H.J. Degenkolb Associates, Inc.
I f
PEER REVIEW GROUP's CENTRAL FINDINGS 4
- 1) The project team did follow the guidance in the NUREGs
- 2) The study was executed in a fully competent and professional manner.
- 3) The study used state-of-the-art methods.
- 4) The study took cognizance of all relevant information.
OTHER COMMENTS by the PEER REVIEW GROUP A_1 Selection of the Review Level Earthauake o more explicit guidance is needed to clarify ambiguities I
E_1 Combining Seismic and Non-seismic Failures o methodology used at MY is not rigorous o PRG recommended that this aspect of the methodology be developed fully .
I o clarification needed as to how " seismic margin"
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is to be
- interpreted . s t .
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,Q CDFM Method vs. Fragilities Method for HCLPF Analysis & i l
o PRG recommended further m thodological devc? nment in
- this area .
Q1 Level of Expertise Needed q
o Fragilities team must have experience in I
o doing detailed walkdowns I o focussing on critical components l o realistically analyzing capacities I o Systems team should have experience with 1 o PRA methods o external-initiators analysis 9
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E). Earthauake ExDerience and Test Data Base ;
o need to document experience data base t o guidance on configuration details must be I strengthened :
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El Relay Chatter y
4 o .Not covered in the MY trial review - '
o PRG believed guidance should be strengthened i in this area ;
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1
.Gl Correlations Amone Earthauake-induced Failures ,
i o PRG identified this as a methodological problem area o HCLPF-type approach isn't well suited to handling correlations well
(
l H1 Screenine Methods Used in the MY Trial Review o PRG endorses the iterative / interactive methods used
l Il l LEVEL OF PEER REVIEW EFFORT o The level of effort spent at Maine Yankee was essential to the project's success l
1 o On the issue of how much routine peer review is needed:
l o Panel was divided 1 1
o Some thought peer review is essential o Some thought the need is no different than for any other utility-type analysis l
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