ML20003H474
| ML20003H474 | |
| Person / Time | |
|---|---|
| Issue date: | 04/14/1981 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-1822, NUDOCS 8105060080 | |
| Download: ML20003H474 (9) | |
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DATE ISSUED:
EXTREME EXTERNAL PHENOMENA
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JANUARY 29-30, 1981
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.: g The ACRS Subcomittee on Extreme External Phenomena held a two-day meeting on January 29-30,'1981 at the Airport Park Hotel, 600 Avenue of Champions, Inglewood, Cali fornia. The purpose of this meeting was to review matters relatiiig to seismic scram, the seismic safety margins research program (SSMRP), and the seismic quali-fication of auxiliary feedwater systems. Notice of this meeting was published in the Federal Register on January 15, 1981. A copy of this notice is included as Attachment A.
A list of attendees is included as Attachment B and the schedule for the meeting is included as Attachment C.
Selected handouts from this meeting are included as Attachment D.
The complete set of handouts is in the ACRS files.
No written statements or requests for time to make oral statements were received from members of the public. The principal attendees at this meeting were:
l P, D. Okrent, Subcommittee Chairman R. Richardson, NRC E
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C. P. Siess, Subcomittee member D. Dong, LLNL M. Bender, Subcomittee member G. Cumingt LLNL
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C1C J. C. Mark, Subcomittee member J. Wells, LLNL 2
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P. Shewmon, Subccmittee member D. Bernreuter, LLNL ha, ag H. Etherington, Consultant M. Bohn, LLNL
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N'* ar '**' d D. Ward, Subcomittee member J. Johnson, SMA S. Saunders, Consultant A. Cornell, MIT
%s'S M. White, Consultant T. Y. Chuang, LLNL t
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Z. Zudans, Consultant J. Knight, NRC G. Thompson, Consultant R. Gupta, NRC J. Maxwell, Consultant P. Smith, LLNL R. Savio, ACRS Staff S. Bush, BOL The meeting was begun at 8:30 am on Thursday, January 29, 1981 and was adjourned at 6:35 pm on that date. The meeting was reconvened at 8:30 am on Friday, January 30, 1981 and was adjourned at 3:45 pm on that date.
The entire meeting was held l
in open session.
t INTRODUCTION Dr. Okrent opened the meeting with a short introduction in which he summarized the purpose and the goals for the Subcomittee meeting.
SEISMIC SCRAM - J. RICHARDSON, NRC Mr. Richardson sumarized the current status of the NRC investigations on the advisability of the seismic scram. The NRC sponsored study at LLNL had investigated 8195060080
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low-level seismic scrams and had concluded that safety benefits of low-level scrams were marginal at best. The NRC plans to examine high-level seismic scram work via work sponsored at LLNL.
The results of this work are expected to be available by th,e end of FY 81.
High level seismic scrams (approximately 2/3 the equivalent of the SS) are used by the Japanese.
The scrams have not proved to be operational inconvenience. The NRC Staff has discussed the use of high-level seismic scrams with the Japanese but has been unable to uncover the regula-to'y philosophy that the Japanese use in deploying such scram devices.
SSMRP INTRODUCTION J. RICHARDSON, NRC Mr. Richardson summarized the status of the SSMRP research. He indicated that the program objectives were to develop methods of es'timating the conservatism (or nonconservarism) inherent in the seismic design methods specified in the Standards Review P'lan and to develop, as required, improved safety requirements and methods for safety assessment. The SSMRP work is organized in three phases.
The results of Phase I work has been completed. This part of the program was directed towards developing the methodology, using the probabilistic methods to evaluate the Zion plant, and to performing some sensitivity studies to identify the most critical aspects of the input / analysis methods.
The final report on Phase I is expected by March 1981. The Phase II portion of this work will deal with the improvement and validation of the methodology and the completion of the sensitivity studies. The probabilities of release which is associated with various seismic induced accident scenarios will be calculated in the Phase II portion of the work. The Phase III portion of' the work will be recommended changes to the Standard Review Plan. Completion of the SSMRP work is expected in mid 1984.
A listing of the major milestones in the Phase I portion of the work is given on page 1 of Attachment D.
There was some discussion as to the use of the SSMRP work in the licensing process and as to the ultimate program goals. The Phase I work has prcduced a series of computer codes which could be used in the' licensing
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evaluations. The analysis of the implications of the Zion study is not yet com-pleted. It is expected that this will give an improved licensing perspective to the adequacy of the currently employed seismic design methods..The SSMRP tech-niques are currently being applied to the analysis of the nonseismic qualified auxiliary feedwater systems in San Onofre 1.
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i 1/29-30/81 EEP OVERVIEW OF THE SSMRP PROGRAM - R. DONG, LLNL Mr. Dong summarized the status of the SSMRP work.
The sumary of the managerial responsibilities for various aspects of the SSMRP program are given on page 2 of Attachment B.
A sumary of the computational procedures used in this work is given on page 3 of Attachment D.
The major codes which have been developed are the SMACS, BE/ EMS, and SEISIM codes. The Phase I work is completed. The objectives of the Phase I work are believed to have been met and a probabilistic computational procedure has been constructed using, for the most part, state-of-the-art method-ology. The computational procedure has been demonstrated by the application to the Zion plant. Event trees for selected initiating events were constructed for the Zion studies. Tnese were for the full range of LOCA events, the Transient I Fault and Transient II sequences, and the reactor pressure vessel rupture event.
trees were constructed for the auxiliary feedwater system, the service water system the residual heat removal system, the safety injection system, the reactor coolant loop system, and the electrical power system. Thirty time histories were used in the seismic input for six acceleration ranges (.15.30g,.30 to.45g,.45 to.60,
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.60 to.75g,.75 to.90g, and.90g an'd above). The HAZARD code was used to generate response spectra. The fragility data used was obtained from the available experi-mental data, the design information from the Zion plant, and a survey of subjec-tive expert opinion. The structures considered in the analysis were the contain-ment building, the internals of the containment building, the auxiliary-turbine building and the crib house. Log-normal fragility curves were used. The random and modeling uncertainties were not separated in this analysis.
In the soil-struc-ture interaction review the FLUSH and LLASSIX I and one-dimensional linear and non-linear techniques were :ompared. The analysis of the major structural response l
included structural analysis techniques review, and assessment of dampening magni-f tudes, and assessment of the uncertainties in the estimated response frequencies f
and dampening.
In the piping analysis the pipe support was assumed to be rigid and l
unable to fail. A simolified SMACS sensitivity analysis on subsystem response was performed within the Phase I work. Much of the work is considered as being plant specific to the Zion plant. The development of the seismic input, the fragility treatment, the event trees, the HAZARD, SMACS, and SEISIM codes will, however, have generic applications.
d 4
e-EEP 1/29-30/81 Mr. Dong summarized the current assessment of the uncertainties in the seismic design process.
Mr. Dong stated that the Zion wor'k had only been recently com-pleted and the results had not been fully evaluated at this time. However, on the basis of the current assessment of this work, the major uncertainties in the calculated response are, in decreasing order, a) the determination of pipe movements, b) the determination of piping acceleration and c) the determination of building acceleration. The major contributors to the uncertainty in the estimation of the probability of release and system failure are judged to be, in this order, a) systems not treated in the fault trees, b) the determination of responses, c) the determination of fragilities, d) the incomplete treatment of the full scope of initiating events, and e) the determination of the seismic input. The major contributors to the' seismic input uncertainty are, in this order, a) the gr.ound motion model, b) local site effects, c) the determination of the largest expected earthquake, and d) the proper zonation of earthquake zones.
In the soil-structure interaction analysis the largest uncertainties, in this order, are a) the definition of the free field ground motion, b) the modeling of soil properties, and c)'the adequacy of the analysis techniques.
The major uncertainty in the modeling structurc; was judged to be the uncertainty in the basic structural modeling. The dampening uncertainty was judged not to be important as was thought at the beginning of the= work. The major contributors to subsystem response uncertainty are the modeling of support behavior and the estimation of appropriate dampenings. The fragility analysis contains many sig-ni ficant contributors to the overall uncertainty. The principal contributors are l
the fragility of electrical components (particularly relays and breakers), instru-l mentation (sensors and associated electronics), the diesel generator accessories.
piping, the treatment of valve fragility data, the spring operated safety relief l
I valve, and the fragility of cable tray assemblies.
1 It is expect 9d that the insight into the process that was gained from the Zion analysis will make possible the simplification of the future analysis. The use of expert upinion to augment the available seismic data and the evaluation of the uncertainties in the seismic hazard curves is considen!d as one of the major results of the SSMRP work. The codes that were generated by phase I of the SSMRP work will permit rigorous seismic risk calculations to be perfomed with reasonable expenditures of computer time. Major steps are considered to have been made in
. 1/29-30/81
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EEP the evaluation of state-of-the-art soils-structure interaction methods and in the construction of a fragility data base.
SYSTEMS ANALYSIS - C. CUMMINGS/J. WELLS, LLNL Mr. Cummings and Mr. Wells summarized the results from the systems analysis seg-ment of_ the Phase I SSMRP work. The SEISIM computer code had been developed as the computational tool for this part of the analysis. The code is used in the event and fault tree development for the systems modeling. The code was developed and used in the Zion analysis. Event trees were developed for reactor ' essel v
rupture, a full range of LOCA events, the T1 and T2 transients and containment Random failures were treated in a manner similar to what was used in failure.
the WASH-1400.
Common mode failures, as identified, were reviewed for each fault
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tree and modeled as appropriate. The calculated release category probabilities are summarized on page 4 of Attachment D.
SEISMIC INPUT - D. BERNREUTER, LLNL Mr. Bernreuter discussed the development of the probabilistic description of the earthquake hazard and the Zion plant site. The result is given on page 5 of This was developed utilizing the available earthquake hazard data, Attachment D.
It was noted that coupled with use of a systematic survey of expert opinion.
there were significant differences among experts as to the appropriate seismic zonation of the Eastem U.S.
The significance of the uncertainty in the seismic zonation is regionally dependent and, for the Zion site, causes the ground accelera-tion to vary in the range of 15 to 25 percent.
Different ground motion models were found to lead to large variations in the peak ground acceleration and the spectro shape of the earthquake response. The other certainty associated with It was signi fi-the ground motion model was judged to be an important parameter.
cant variation among the experts with regard to the largest earthquake that could occur in each seismic zone. This variation was generally two to three magnitude units and leads to significant variations in the estimation of the seismic ~ hazard at the Zion site.
FRAGILITIES - M. B0HN, LLNL_
Structural Mr. Bahn summarized the SSMRP development of a fragility data base.
component analysis, the t sailable data base, and the systematic survey of expert
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'EEP - 1/29-30/81 opinion were used to develop the data base.
Failure for structures was defined in the analysis to be when the elastic deformation.of the structure interferred with the operation of safety related equipment.
For most of the cases examined considerable margin existed before collapse.
Commercial data, military data obtained in missile site hardening test programs, and data obtained from the The testing of nuclear plant components were used in the component data base.
results of this work were reviewed by a panel of fragility experts. The review was directed toward an appraisal of a basis method and the data base used.
The systematic survey of expert opinion utilized in this work was extensive.
Four hundred experts were identified of which 250 agreed to participate. One hundred and fifty actually completed the questionnaires which were assembled and sent out by LLNL.
STATISTICAL RESPONSE (SMACS) - J. JOHNSON, SMA l
Mr. Johnson described the results of the SMACS application to the Zion evaluation.
The seismic input, the soil structure interaction effects, the structural models, and the subsystem models are input into the SMACS code. System responses are calculated for each set of inputs.
The results of this analysis are completed and are being evaluated by the SSMRP.
SENIOR RESEARCH REVIEW GROUP - A. CORNELL,MIT/S. BUSH, BNL A Senior Research Review Group had been appointed to independently review the SSMRP work.
The review group consisted of A. Cornell (MIT), S. Bush (BNL), W.
Hayes (USGS), and N. Newmark (Univ of IL).
Mr. Bush and Mr. Cornell were present at the meeting and reported to the Subcommittee on the progress of the SSMRP work.
Mr. Hayes was unable to attend and. reported by way of a written statement which I
was read into the record. Mr. Bush, Mr. Cornell, and Mr. Hayes generally felt that the work was progressing and was successful. Continuation of this work was supported.
It was noted that the fragility data used was useful in making relative comparisons of plant systems and probably could not be taken as represeating absolute failure points. The need for addressing functional reliability in the i
fragility base and for examining the effect of the relative rigidity of the pipe I
systems was stressed. The meeting was adjourned at 6:35 pm on this date and was reconvened at 8:30 am on Friday, January 30, 1981.
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EEP 1/29-30/81 SSMRP APPLICATIONS TO LICENSING - J. RICHARDSON, NRC Mr. Richardson discussed what he believed were the useful licensing applications of the Phase I of the SSMRP work. Mr. Richardson stated that the Phase I work would aid in focusing the licensing safety reviews on the most important issues and in focusing research and development efforts in the most productive areas.
He indicated that he believed that the results would aid in stabilizing the licensing safety evaluations in that the margin could now be better defined and would be useful in evaluating seismic safety improvements for a given plant.
He noted that the seismic input element of tne SSMRP will play ~a significant role in the SEP evaluation. The calculational methods developed in the SSMRP will be used in an assessment of the PWR auxiliary structure interaction can be a useful tool in resolving some of the controversy in this area. The computer codes developed in the SSMRP work (SMACS, SEISIM, ARAMA) can be used for seismic design margin analysis.' Subcommittee members recommended that an increased effort would be made to orientate the SSURP work towards an early input into the licensing product and close coordination should be maintained with the cognizant licensing personnel.
SOIL STRUCTURE INTERACTION - J. JOHNSON, SMA Mr. Johnson indicated that there were several. objectives in the soil-structure interaction portion of the SSMRP work. They were a) to identify and a:sess a relative importance of the various facets of soil structures interaction; b) to review existing methods under development for performing soil structure interac-tion analysis and to estimate their accuracy; c) to identify the sources of uncer-tainty in the soil-structure interaction process; d) to recommend benchmark analy-sis and test problems to be used in-the verification of the soil-structure i interaction analysis procedures; and e) to recommend procedures for the Phase II portion of the SSMRP work. The state-of-the-art analysis for soil-structure interaction was discussed. The two methods which are available are the direct method and the substructure method. Complex three-dimensional configurations require the substructure approach. The LLNL recommendations for improving the state-of-the-art are; a) the performance of research directed towards the better definition of free field motion; b) further evaluation of the nonlinear aspects of soil behavior; c) the development of improved benchmark problems; d) an expanded use and analysis of the existing full scale field data, i
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. 1/29-30/81 EEP MAJOR STRUCTURAL RESPONSE - J. JOHNSON, SMA Mr. Johnson described the structural response analysis before the Zion plant.
Four modeling configurations were used. A schematic of the Zion structures and the four modelings of the structural geometry are shown on pages 6-10 of Attach-Summaries of some of the results are presented on pages 11-12 of Attach-ment D.
The estimated dampening values were compared to the Reg. Guide 1.61 ment D.
specified values. These results are summarized on page 13 of Attachment D.
SUBSYSTEM RESPONSE - T. Y. CHUANG, LLNL Mr. Chuang summarized the work done under the subsystem response task of the SSMRP work. The primary objective of this work was to compute response parameters given the input environment for those components and systems identified as impor-tant in the faul.t tree analysis. The systems which were treated in the Zion analysis were 1) the auxiliary feedwater system; 2) the service water system;
- 3) the residual heat removal system; 4) the safety injection system; 5) the com-ponent cooling water system; 6) the containment spray system; 7) main steam and Linear elastic analy-main feedwater systems; and 8) the reactor coolant system.
sis and the multiple support time history method were used.
The uncertainty contributions in the dynamic modeling of the piping systems were found to contri-bute significantly to the overall uncertainties.
AUXILI ARY FEEDWATER SYSTEM SEISMIC STUDY - T. Y. CHUANG, LLNL Mr. Chuang described the proposed application of the SSMRP methodology to the nonseismic qualified auxiliary feedwater system issue. The post-TMI examination of PWR auxiliary feedweter systems. revealed that there were 10 plants in which the auxiliary feedwater systems were not seismically qualified to current standards.
The SSMRP methods will be applied to the analysis of the San Onofre 1 auxiliary If this is successful'the technique will be used to evaluate feedwater system.
other plants in this class.
Additional information can be obtained from the NRC public Document Room, NOTE:
1717 H Street, NW, Washington, D.C. 20555 or at cost from the Alderson Reporting Company, Inc, 400 Virginia Avenue, S.W., Washington, D.C. 20024.
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MAJOR EVENTS OF PHASE I NOVEMBER 1977 INITIAL CONCEPTS FOR SSMRP i
FEBRUARY 1978 PROBRAM Fi_AUNING BEGINS i
JULY 1978 AUTHORIZATION TO BEGIN MAJOR TECHNICAL WORK (50% SUBCONTRACTED) l AUGUST 1978 SELECTION OF ZION PLANT
'l MAY 1979 DECISION ON APPROACH TO SSMRP PROBABILISTIC COMPUTATIONAL l
PROCEDURE DECEMBER 1979 SSMRP PHASE I SCHEI)ULE-EXTENSIO!l APRIL 1980 LOAD COMBINATIONS BECOMES A SEPARATE PROGRAM
$l65/nf JULY 1980
-SEISMIC AND SMACS CODES RUNNING
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JANUARY 1981 COMPLETION OF PHASE I ANALYSES f
MARCH 1981 PHASE I FIllAL REPORT I
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.THE SSMRP ENCOMPASSES A DIVERSITY OF TECHNICAL l
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DISCIPLINES NRC LLNL i
J.E. Richardson P.D. Smith Program Manager Deputy Program Manager C.W. Burger R.G. Dong i
l Projects:
i Plant / Site Selection G. Bagchi T.Y. Chuang l
j and Data Collection l
11 Seismic Input R.J. Brazee D.L. Bernreuter Ill Soil-Structure J. Costello J.J. Johnson Interaction IV Major Structural C.W. Burger J.J. Johnson
Response
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Subsystem Response J.J. Burns T.Y. Chuang VI Fragilities J.J. Burns M.P. Bohn l
Vil Systems Analysis J.J. Burns G.E. Cummings/
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i Vill SMACS and BE-EMS C.W. Burger J.J. Johnson I
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RELEASE CATEGORY PROBABILITIES WERE rd.,.c
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2.5E-09 8.6E-10 3.8E-08 3
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USING SEISIM CALCULATED INITIATING EVENT PROBABILITIES USING DIABLO CANYON STUDY INITIATING EVENT PROBABILITIES f (2)
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IN ANOTHER STUDY, WE FOUND THAT ZION DAMPING VALUES CAN BE MUCH LOW E3 t
TilAN R.G.1,61 (NUREG/CR-1661) sSid EST! MATED DAMPlNC LEVELS FOR SEISMIC CATEGORY I STR FOR VARYING FREE FIELD GROUND ACCELERATION LEVELS MEDIAN DAMPING
(% OF CRITICAL)
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5 7
10 VALUES (%)
REACTOR BUILDING CONTAINMENT VESSEL 0.65G 1G 1.3G S
CONCRETE INTERNALS 2.7G 4G 5.5G 7
AUXILIARY BUILDING 0.35G 0.5G 0.7G 7
CRIB HOUSE 0.350 0.5G 0.7G 7
DAMPING VALUES CORRESPOND TO SEISMIC RESPONSE STRESS LEVELS NOTE:
ASSUMING NO COINCIDENT LOCA
%