ML17146B083
| ML17146B083 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 12/22/1987 |
| From: | Thadani M Office of Nuclear Reactor Regulation |
| To: | Butler W Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8712240189 | |
| Download: ML17146B083 (39) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 December 22>
1987 MEMORANDUM FOR:
Walter R. Butler, Director Project Directorate I-2 Division of Reactor Proiects I/II FROM:
SUBJECT:
Mohan C. Thadani, Project Manager Proiect Directorate I-P.
Division of Reactor Projects I/II MFETING WITH PENNSYLVANIA POWER AND LIGHT COMPANY TO DISCUSS INSIGHTS GAINED FROM SUSQUEHANNA INDIVIDUAL PLANT EVALUATION On December ll, 1987, at the staff's request, the Pennsylvania Power and Light Company (PP8L) provided a briefing of (1) the methodology used to perform the Susquehanna Individual Plant Evaluation
( IPE), (2) the results of the analysis, (3) the PPAL insights and interpretation of the results, and (4) the PP8L view of the risk assessment.
Enclosure l is a copy of the viewgraphs used by the PPSL for the briefing, and Enclosure 2 is a list of attendees.
The PP8L indicated that one of its objectives in risk assessment was to assure that all possible capability of the plant will be utilized to prevent and mitigate the consequences of severe accidents.
Its fundamental policy was to assure defense-in-depth for all equipment and procedures.
The PPEL incorporated realistic human performance models which were subsequently verified by measurements on the Susquehanna simulator.
The results of the PPEL analysis indicated that by proper use of all the equipment and the plant capabilities core damage sequences can be arrested before vessel failure occurs 70K of the time, and by the proper use of the wetwell venting the containment overpressure failures for sequences which would result in core melt and vessel failure can be reduced by a factor of 10.
Based on its experiences with the Susquehanna IPE analysis, the PPBL does not consider a low bottom line calculated frequency as a proof of adequacy.
Rather, it considers that the IPE should be directed to evaluate the defense-in-depth which gives the best available protection against not only the anal.yzed sequences, but also unanalyzed sequences.
The PPSL thinks that the utilities can derive the greatest safety benefit from an IPE if they perform in-house 'analyses rather than assign full responsibilities to contractors.
All accident sequences analyzed in the IPE should be carried to a stable state or failure to ensure that defense-in-depth capabilities of all equipment and procedures are identified and harnessed at each successive accident stage, in conjunction with the symptom based procedures.
87i2240i89 87i222 PDR ADOCK 05000387 P
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The PP&L recommended tha't the Commission perform research to develop criteria which enhance core/vessel stabilization and core debris/containment stabilization.
The IPE Generic Letter should require a phased approach and assure that each accident sequence be carried, to a stable state or failure, and defense-in-depth for plant-specific equipment'and procedures be demonstrated for all successive stages of accident sequences.
It When asked to estimate the resources required to do the IPE, the PP&L replied that they had used five people for a cumulative one person-year effort.
The level of effort was based on a high level of'preparation and having a completed PRA.
Enclosure:
As stated Mohan C. Thadani, Project Manager Project Directorate I-2 Division of Reactor Projects I/II cc:
Service list DISTRIBUTION PDI-2 Reading MThadani/DFischer MO'Brien Larry Shao Ashok Thadani Richard Barrett S.
A. Varga M.
C. Thadani Tom Murley Mark Caruso John C.
Lane William Beckner James Norberg Cecil Thomas Wayne Hodges Glenn Kelly W.
R. Butler Bruce Boger Franklin Coffman Ron Hernan Hge TER.
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~ >/ar+lou3 A~RS Ceo) pg C/ayW4 Previously concur ed*
PDI-2/PM*
MThadani:mr 12/22/87 PDI-2/D*
WButler 12/22/87
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ll IF IF ll The PPSL recommended that the Commission perform research to develop criteria which enhance core/vessel stabilization and core debris/containment stabilization.
The IPE Generic Letter should require a phased approach and assure that each accident sequence be carried to a stable state or failure, and defense-in-depth for plant-specific equipment and procedures be demonstrated for all successive stages of accident sequences.
h'hen asked to estimate the resources required to do the IPE, the PPSL replied that they had used five people for a cumulative one person-.year effort.
The level of effort was based on a high level of preparation and having a completed PRA.
Enclosure; As stated Mohan C. Thadani, Project Manager Project Directorate I-2 Division of Reactor Projects I/II cc:
Service list
Mr. Harold W. Keiser Pennsylvania Power
& Light Company Susquehanna Steam Electric Station Units 1
& 2 CC:
Jay Silberg, Esq.
Shaw,'ittman, Potts
& Trowbridge 2300 N Street N.W.
Washington, D.C.
20037 Bryan A. Snapp, Esq.
Assistant Corporate Counsel Pennsylvania Power
& Light Company 2 North Ninth Street Allentown, Pennsylvania 18101 Mr. E. A. Heckman Licensing Group Supervisor=
Pennsylvania Power
& Light Company 2 North Ninth Street Allentown, Pennsylvania 18101 Mr. Loren Plisco Resident Inspector P.O.
Box 52 Shickshinny, Pennsylvania 18655 Mr. R. J.
Benich Services Project Manager General Electric Company 1000 First Avenue King of Prussia, Pennsylvania 19406 Mr. Thomas M. Gerusky, Director Bureau of Radiation Protection Resources Commonwealth of Pennsylvania P. 0.
Box 2063 Harrisburg, Pennsylvania 17120 Robert W. Alder, Esquire Office of Attorney General P.O.
Box 2357 Harrisburg, Pennsylvania 17120 Mr. Jesse C. Tilton, III Allegheny Elec. Coorperative, Inc.
212 Locust Street P.O.
Box 1266 Harrisburg, Pennsylvania 17108-1266 Mr.
W. H. Hirst, Manager Joint Generation Projects Department Atlantic Electric P.O.
Box 1500 1199 Black Horse Pike Pleasantville, New Jersey 08232 Regional Administrator, Region I U.S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pennsylvania 19406
OBJECTIVES 0
TO DESCRIBE PPRL RISK ASSESSMENT EFFORTS OBJECTIVES PROCESS RESULTS FUTURE ACTIVITIES
PRESENTATION OUTLINE 0
INTRODUCTION PPRL OBJECT IYES 0
PPRL EXPERIENCE IN RISK ASSESSMENT 0
PP8L APPLICATION OF THE IPE METHODOLOGY 0
RESULTS OF THE SUSQUEHANNA IPE 0
FUTURE DIRECTIONS FOR PP8L RISK ASSESSMENT 0
SUMMARY
THE PPRL APPROACH TO RISK ASSESSl'EHT INTENT ME WISH TO ASSURE THAT ALL POSSIBLE CAPABILITY OF THE PLANT TO PREVENT OR NITIGATE THE CONSEQUENCES OF PLANT DANAGE FOR ANY INITIATING EVENT AND ANY CONBINATION OF EQUIPNENT FAILURES HILL BE EFFICIENTLY AND EFFECTIVELY APPLIED,
OBJECTIVES OF RISK ASSESSMENT AT PPRL 0
ME USE RISK ANALYSIS METHODS TO:
EVALUATE ALTERNATIVES FOR PLANT MODIFICATIONS DEVELOP OPTIMAL EMERGENCY OPERATING PROCEDURES DEVELOP OPERATOR TRA INING PROGRAMS TO ASSURE OPERATOR KNOWLEDGE OF CRITICAL RESPONSE ACTIONS IDENTIFY POTENTIAL MINOR MODIFICATIONS HHICH CAN REDUCE THE FREQUENCY OF OR MITIGATE THE CONSEQUENCES OF SIGNIFICANT SEVERE ACCIDENT SEQUENCES TRAIN AND INFORM MANAGEMENT TO ASSURE PROPER COORDINATION OF RISK IN DECISION MAKING ASSURE "DEFENSE IN DEPTH" IN OUR EQUIPMENT AND OUR PROCEDURES, DEMONSTRATE A HIGH LEVEL OF SAFETY IN SUSQUEHANNA OPERATIONS.
DEFENSE IN DEPTH DEFINITION EQUIPMENT; 0
PLANT DANAGE MILL OCCUR ONLY AFTER INDEPENDENT FAILURE OF REDUNDANT AND DIVERSE EQUIPNENT 0
IN THE ABSENCE OF ADDITIONAL FAILURES BEYOND THOSE CAUSING CORE DAMAGE, THE CORE DANAGE SEQUENCE CAN ALWAYS BE ARRESTED BEFORE REACTOR VESSEL FAILURE 0
NO CONBINATION OF FAILURES CAUSING CORE DANAGE CAN CAUSE UNAVOIDABLE CONSEQUENTIAL CONTAINMENT FAILURE PROCEDURES; 0
NO PROCEDURE WILL HAVE ADVERSE CONSEQUENCES IN THE CASE OF ADDITIONAL EQUIPNENT FAILURES BEYOND THOSE OCCURRING INITIALLY 0
THE NECESSARY ANTICIPATORY ACTIONS MILI BE PERFORNED TO AVOID LOSS OF ADDITIONAL EQUIPNENT 0
THE NECESSARY ANTICIPATORY ACTIONS MILL BE PERFORNED TO PERNIT SUCCESSFUL
RESPONSE
TO POTENTIAL ADDITIONAL
- FAILURES,
,PPaL EXPERIENCE -
PRA o
PPRL CONTRACTED IN 1980 FOR A LEYEL 3 PRA PITH NUS CORPORAT IOil, o
THIS EVOLVED INTO A JOINT PPRL-NUS EFFORT IN 1983 WHICH RESULTED IN A DRAFT DOCUMENT.
o WHILE THE NUS L.'ORK HAS PERFORMED COMPETENTLY IN ACCORDANCE HITH ACCEPTED PRA PRACTICE, PPRL HAD RESERVATIONS ABOUT HOM ACCURATELY SUSQUEHAiNNA HAD BEEN REPRESENTED, o
OUR INITIAL IN-HOUSE EFFORT WAS TO REVISE THE DRAFT DOCUMENT TO BETTER REPRESENT OUR PLANT EQUIPMENT RESULTING IN A REVISION 0 LEVEL 1 PRA DOCUMENT, o
OYER THE PERIOD 1981 - 1985 ME HAD PERFORMED EXTENSIVE STUDIES ON STATION BLACKOUT AND ATLAS FOR SUSQUEHANNA AND HAD DEYELOPED TRANSIENT ANALYSIS METHOD FOR THESE TRANSIENTS,
LESSONS LEARNED PRA o
BASED ON OUR EXPERIENCES IN REVIEWING NUS
ASSURE FULL USE OF ALL PLANT CAPABILITY IN
RESPONSE
TO AN ACCIDENT, ASSURE THAT OUR PROCEDURES, WOULD ACCONPLISH
- THIS, PERFORM SUSQUEHANNA SPECIFIC ANALYSIS TO ASSURE USE OF CREDIBLE SUCCESS
- CRITERIA, EXPLICITLY REPRESENT THE TINING OF CORE DAMAGE AND CONTAINNENT FAILURE, CARRY THE ANALYSIS TO A STABLE OR COMPLETELY FAILED PLANT CONDITION, AVOID CONVENTIONAL CONSERVATISNS RELATING TO CONNON MODE FAILURE, UTILIZE THE NAAP CODE AS THE BASIS FOR CORE DANAGE PROGRESSION,
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THE PPaL APPLICATION OF THE IPE NETHODOLOGY 0
WE CONSIDERED THE BNR IPE METHODOLOGY TO BE DEFINED 17; THE SYSTEM DEPENDENCY NATRICES THE QUANTIFIED FUNCTIONAL FAULT BEES THE QUANTIFIED EVENT TREES 0
THESE WERE CONPARED TO SSES SYSTEMS AND PROCFDURES AND EDIFIED TO REFLECT DIFFERENCES IN:
SYSTEM DEPENDENCE PLANT SYSTEMS PLANT OPERATION OPERATING PROCEDURES 0
SUSQUEHANNA SPECIFIC INFORNATION WAS USED TO DEVELOP SYSTEM DEPENDENCIES AND QUANTIFY THE FUNCTIONAL FAULT TREES
.0 EXTENSIVE ANALYSIS WAS PERFORNED TO ESTABLISH REALISTIC SUCCESS CRITERIA 0
CORE STABILIZATIONCRITERIA TO PRESERVE REACTOR YKSSEL INTEGRITY WERE DEFINED' AN ACCIDENT CLASSIFICATION SCHENE WAS DEVISED' A NEANS FOR ASS16NING CONDITIONAL PROBABILITY TO VESSEL FAILURE AND LOSS OF CONTAINMENT INTE6RITY WAS SEYISKD fOR SEQUENCES WHICH ENDED IN CORE DAJQGE.
0 DEFINED FOUR PLANT DAMAGE CATEGORIES CORE DAMAGE (CLAD ONLY OR LIMITED MELT)
CORE KELT AND VESSEL FAILURE KETWELL VENT WITH CORE DWELT AND VESSEL FAILURE CONTAINMENT OYERPRESSURE FAILURE WITH CORE l%LT Al VESSEL FAILURE
THE PPRL APPLICATION OF THE IPE METHODOLOGY ANALYTICALAPPROACH o
THE PP&L APPROACH WAS DOMINATED BY PRIOR WORK ON NON-PROBABILISTIC RESPONSE STRATEGY EVALUATIONS FOR STATION BLACKOUT AND ATWS, o
AN ATTEMPT WAS MADE TO RECOGNIZE AND AVOID CONVENTIONAL PRA CONSERVATISMS AND ASSUMPTIONS WHICH HAVE A STRONG INFLUENCE ON'EVENT SEQUENCE PROGRESSION, o
WE HAVE EXAMINED ALL EVENT SEQUENCES TO ASSURE THAT OUR PROCEDURES LEAD TO THE CORRECT AND TIMELY RESPONSE
- ACTION, o
WE HAVE DEVELOPED SUSQUEHANNA UNIQUE SUCCESS CRITERIA BASED ON SUSQUEHANNA EQUIPMENT PERFORMANCE, o
WE HAVE USED OPERATING EXPERIENCE IN PREFERENCE TO THEORETICAL MODELS FOR EQUIPMENT UNAVAILABILITY,
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THE SUSQUEHANNA IPE UNIQUE FEATURES o
HUMAN ERROR ERRORS DURING NORMAL PLANT OPERATIONS ARE CONSIDERED AND ARE IMBEDDED IN EQUIPMENT UNAVAILABILITIES,AND INITIATING EVENTS, CONTROL ROOM OPERATORS MERE ASSUMED TO FOLLOW EMERGENCY OPERATING PROCEDURES WITHOUT ERROR.
CONTROL ROOM OPERATORS AND SUPPORT PERSONNEL FAIL TO EXECUTE PROCEDURES ONLY MHEN TIME IS
- LIMITED, o
DECAY HEAT REMOVAL QUANTIFIED RHR UNAVAILABILITYBY PRECURSOR
- METHODS, INTRODUCED USE OF THE RMCU BLOMDOMN MODE FOR DECAY HEAT REMOVAL FOR TRANSIENT INITIATORS.
WETMELL VENT WAS INTRODUCED FOR LOCA AND STATION BLACKOUT EVENTS,
THE SUSQUEHANNA IPE UNIQUE FEATURES (CONTlNUEo) o ANTICIPATORY ACTIONS ACTIONS REQUIRED TO PREVENT PREDICTABLE LOSS OF EQUIPMENT, ACTIONS REQUIRED TO ASSURE MITIGATION CAPABILITY IN THE EVENT OF ADDITIONAL EQUIPMENT FAILURES, THE TRIGGER FOR SUCH ACTIONS IS SYMPTOM BASED.
o ATWS TREATMENT THE NECESSARY
RESPONSE
PROCEDURES ARE STRONGLY DEPENDENT ON THE TYPE OF ATWS AND COINCIDENT EQUIPMENT FAILURES, WE HAVE PARTITIONED ATWS EVENTS ON THE BASIS OF ISOLATION STATUS, SCRAM RELAY FAILURES, SINGLE SDV FAIlURE, DOUBLE SDV FAILURE, WE ASSUME THE ABILITY TO MANUALLYDRIVE RODS IN WITH THE CRD PUMPS WHEN AVAILABLE.
WE POSTULATE MECHANICAL CLAD DAMAGE WHEN THE REACTOR MUST BE DEPRESSURIZED IN A CRITICAL CONDITION.
aC
~ ti THE SUSQUEHANNA IPE UNIQUE FEATURES (co~~i~uco) o EVENT SEQUENCE CLASS DEFINITIONS CLASS SPECIFIES STATE OF
- CORE, REACTOR VESSEL, AND CONTAINMENT AND TIME OF DAMAGE TO CORE AND CONTAINMENT, PLANT STATUS FOR EACH EVENT SEQUENCE KNOMN PERMITTING MINIMUM EFFORT TO DETERMINE CONTAINMENT DISPOSITION, THE CONTAINMENT QUANTIFICATION WAS PERFORMED IN THE SSES
- IPE,
EVALUATION OF ATWS EVENTS 0
PART ITIONI NG ELECTR I CAL/f'lECHANI CAL
=
2; 1 SINGLE SDY/TWO SDV
=
100:1 RANDOM FAILURE 0
~ 0 TRANSIENT ANALYSIS EVALUATE ALTERNATIVE RESPONSE ACTIONS EXAMINE DEGRADED PLANT CONDITIONS 0
DEPRESSUR I ZATI ON RAISED HCTL CURVE DEPRESSURIZE ONLY WHEN HCTL IS EXCEEDED OR WHEN HIGH PRESSURE INJECTION IS LOST 0
MANUAl ROD INSERTION ALWAYS SUCCEED BEFORE CONTAINMENT FAILURE 0
ANTICIPATORY ACTIONS CAN ALWAYS AVOID LOSS OF INJECTION
APPLICATION TO ATMS PRESENT IPE SINGLE SLCS PUMP NO ARI NO PART ITIONING NO HPCI BYPASS PROCEDURAL ERROR (10X)
MASH - 1000 NUREG - 1150 CORE DAMAGE 9.3 x 10 9 1,8 x 10-8 2.2 x 10 7 2.2 x.ZO-'.5 x 10 5 4.1 x 10 5 Q) +
COPF
';2 x 10 +
2,2 x }O-u 6 3 x }0-lX 7,2 x }O 7.2 x 10-~
2.0 x }0
}.3 x }0
}.0 x M+
'ORE DANGE WITH CONTAINMENT OVERPRESSURE FAIt.NE
SUSQUEHANNA SIMULATOR MEASUREMENTS BACKGROUND o
A SYSTEM 1 VALIDATION PROGRAM HAD BEEN PLANNED FOR EARLY 1987 TO DEMONSTRATE THE ADEQUACY OF OUR PROCEDURES, OPERATOR TRAINING, AND CONTROL ROOM FACILITIES TO COPE WITH A SEVERE ACCIDENT, o
THE SUSQUEHANNA IPE TOOK A NEW APPROACH TO QUANTIFICATION OF OPERATOR
- ERROR, MAINTENANCE AND SURVEILLANCE ERRORS ARE IMBEDDED IN HISTORICAL DATA ON UNAVAILABILITY AND INITIATING EVENTS CONTROL ROOM OPERATOR ERROR DURING NORMAL OPERATION IS IMBEDDED IN INITIATING EVENT RECORDS ALWAYS FOLLOWS PROCEDURES IN RESPONSE TO AN INITIATING EVENT ONLY FAILS TO EXECUTE A PROCEDURE WHEN TIME IS LIMITED o
PPRL MANAGEMENT SAW A NEED TO DEVELOP SUPPORTING INFORMATION FOR THE SUSQUEHANNA IPE AND APPROVED USE OF THE SYSTEM 1 VALIDATION FOR THIS PURPOSE
SUSQUEHANNA SIMULATOR MEASUREMENTS PRELIMINARY OPERATOR PERFORMANCE OBSERVATIONS o
NO CLEAR CASE OF PROCEDURAL ERROR MAS OBSERVED OUT OF APPROXIMATELY 1650 PROCEDURAL STEPS, o
A FEW INSTANCES MERE OBSERVED WHERE PROCEDURAL AMBIGUITY OR LACK OF PRECISION CAUSED QUESTIONABLE
RESPONSE
- ACTIONS, o
OUR GENERAL PERCEPTION OF THE UNANALYZED EXECUTION TIME DATA IS THAT THE SUSQUEHANNA IPE IS PROBABLY CONSERVATIVE, o
THERE MAY BE DEFICIENCIES IN OPERATOR PERFORMANCE IN TAKING ANTICIPATORY ACTIONS,
0
SUMMARY
OF IMPORTANT RESULTS 0
TOTAl PLANT DAMiAGE FREQUENCY HAS BEEN REDUCFD BY 10Q 0
ATWS AND TRANSIENTS HAVE BEEN ELIMINATED AS DOMINANT CONTRIBUTORS (CONVENTIONAL RESULTS SHOW IMPORTANCE OR DOMINANCE)
- 0 CONTAINMENT FAILURE HAS BEEN SHOWN TO OCCUR IN ONLY 2.5X OF PLANT DAMAGE SEQUENCES (CONVENTIONAL RESULTS ARE NEAR 100X) 0 THE CORE DAMAGE SEQUEN CAN BE ARRESTED BEFORE REACTOR VESSEL FAILURE ABOU 70X F THE TIME (CONVENTIONAL RESULTS ARE OX) sb9
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0 STATION BLACKOUT HAS BECOMiE THE DOMINANT CONTRIBUTOR TO PLANT DAMAGE (WITH FAILURE OF HPCI AND RCIC TO START) 0 THE WETWELL VENT (AS ASSUMED IN THE STUDY)
HAS REDUCED CONTAINMENT OVERPRESSURE FAILURE WITH CORE MELT AND VESSEL FAILURE BY ABOUT 10, (RESOLUTION OF THE VENTING ISSUE IS BEING STUDI ED, )
0 VULNERABILITIES HAVE BEEN DISCOVERED FOR VARIOUS ACCIDENT SEQUENCES WHICH CAN BE ELIMINATED THROUGH PROCEDURES'RAINING AND MINOR PLANT MODIFICATIONS
PLANT VULNERABI LITIES IDENTIFI ED BY THE SUSQUEHANNA INDIVIDUALPLANT EVALUATION 0
EMERGENCY SERVICE MATER FAILURES
- 0 DC POWER ENDURANCE IN STATION BLACKOUT 0
STATION BLACKOUT WITH FAILURE OF HPCI/RCIC START 0
RESET ON HIGH LEVEL FEEDWATER TRIP 0
SUCTION TRANSFER OF HPCI ON HIGH SUPPRESSION POOL LEVEL 0
LOW PRESSURE ECCS INJECTION PERNISSIVE 0
LOSS OF DECAY HEAT RENOVAL
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LESSONS LEARNED I PE 0 0
ASSUMPTIONS OFTEN DRIVE RESULTS 0
f'lUST INVOLVE PLANT PERSONNEL IN REVIEW OF ACCIDENT SEQUENCES 0
DEMONSTRATIOf< OF "DEFENSE IN DEPTH" SHOULD BE OUR OVERALL OBJECTIVE 0
COMBINATIONS OF FIXES CAN HAVE MUCH GREATER IMPACT THAN THE SUM OF THE INDIVIDUAL EFFECTS 0
SUPPORT STATE METHOD IS EXACTLY EQUIVALENT TO MORE CONVENTIONAL METHODS 0
NEED MORE DETAIL IN SUPPORT STATE, DEFINITION 0
LESS SEVERE FAILURES CAN REPRESENT GREATEST THREAT 0
SHOULD PROGRAM THE CALCULATION TO:
REDUCE ERRORS SIMPLIFY RECALCULATION PERMIT MONTE CARLO UNCERTAINTY ANALYSIS 0
BINNING AND CONTAINMENT EVENT TREES ARE INEFFICIENT AND ERROR PRONE AND PREVENT EFF ICIENT TABULATION OF ACCIDENT SEQUENCES 0
LCO CONSTRAINTS CAN BE DIRECTLY INCORPORATED INTO THE COMPUTATION AND ILLEGAL FAILURE COMBINATIONS ARE THUS READILY ELIMINATED 0
DEVELOPED A
GOOD FEEL FOR THE IMPORTANT CONSERVATISMS
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THE PPaL VIEN OF RIStt', ASSESSMENT o
ME DO NOT KNOM THE ACTUAL EXPECTED FREQUENCY OF PLANT DAMAGE TO SUSQUEHANNA BECAUSE OF THE LACK OF COMPLETENESS IN OUR ANALYSIS AND BECAUSE OF THE POSSIBILITY OF ERRORS IN ANALYSIS OR DATA.
o ME DO BELIEVE THAT THE CALCULATED FREQUENCY OF PLANT DAMAGE IS AN ACCURATE ASSESSMENT MITHIN THE LIMITS OF OUR ASSUMPTIONS AND ANALYTICALACCURACY.
o ttE BELIEVE THAT OUR MODELS AND ASSUMPTIONS YIELD THE MOST ACCURATE PICTURE OF THE CAPABILITY OF 00$t PLANT EQUIPMENT AND PROCEDURES OF ANY ANALYSIS METHOD CURRENT Y OOMN.
o Mf BELIEVE THAT OUR USE OF THE IPE TO EVALUATE DEFENSE IN DEPTH"OF BOTH EQUIPMENT AND PROCEDURES GIVES US THE BEST AVAILABLEPROTECTION AGAINST BOTH ANALYZED AND UNFORESEEN EVENTS BECAUSE OF THE USE OF SYMPTOM BASED PROCEDURES,
FUTURE DIRECTIONS FOR PPRL RISK ASSESSMENT 0
THE INITIAL PP8L PERFORMANCE OF AN IPE WAS LACKING IN SEVERAL POTENTIAI LY IMPORTANT AREAS
)
0 WE ARE CURRENTLY DEVELOPING TECHNIQUES TO ELIMINATE THE MOST IMPORTANT PERCEIVED DEFICIENCIES IN THE METHODOLOGY 0
WE WILL PERFORM AN IPE USING PP8L DEVELOPED ACCIDENT CLASSES AND DISPOSITIONING TECHNIQUES TO DEVELOP THE DESIRED SPECTRUM OF PLANT STABLE STATES 0
WE WILL USE THE SUPPORT STATE METHODOLOGY WHICH PERMITS NUMERICAL CALCULATION OF THE STABLE PLANT STATES 0
THERE IS EXTREME FLEXIBILITY IN THE CHOICE OF FINAL PLANT STATES 0
THE CALCULATIONS CAN ALL BE PROGRAMMED FOR COMPUTER AND ARF RELATIVELY SIMPLE AND FLEXIBLE 0
THE MOST EfFECTIVE WAY FOR THE NRC TO DEVELOP CONFIDENCE THAT THE PPRL APPROACH IS SOUND WOULD BE TO ASSIGN AN NRC EMPLOYEE TO PARTICIPATE IN THE ANALYSIS
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FUTURE OBJECTIVE 0
WE WISH TO ACHIEVE CLOSURE ON:
"HOW SAFE IS SAFE ENOUGH?"
WE DO NOT CONSIDER A
LOW BOTTOM LINE FREQUENCY AS PROOF OF ADEQUACY WE WISH TO DEMONSTRATE "DEFENSE IN DEPTH" AS THE MEASURE OF ADEQUACY OF SUSQUEHANNA OPERATIONAL RISK IF WE DEMONSTRATE "DEFENSE IN DEPTH" WE BELIEVE:
THE FREQUENCY OF PLANT DAMAGE FROM INTERNAL EVENTS WILL BE FOUND TO BE EXTREMELY LOW f
OFF-SITE CONSEQUENCES WILL BE FOUND TO BE EXTREMELY LOW BY ANY REASONABLE ANALYSIS,
FUTURE APPROACH 0
WE WILL PERFORN A PROBABILISTIC RISK ASSESSNENT (IPE)
TO DERIVE ALL CREDIBLE EVENT SEQUENCES WHICH CAN LEAD TO PLANT
- DANAGE, 0
WE WILL USE THE SUPPORT STATE NETHODOLOGY, 0
ME WILL PROPAGATE EACH EVENT TREE END POINT.
INDIVIDUALLY.TO DEVELOP THE ENTIRE SPECTRUM OF FINAL STABLE PLANT STATES; FUEL DANAGE FUEL DANAGE WITH VESSEL FAILURE CONTAINNENT FAILURE CONTA I NNENT VENTING VARIOUS DEGREES AND CONBINATIONS OF THE ABOVE 0
FOR EACH fINAL PLANT STATE OF EACH END POINT WE WILL DENONSTRATE THAT "DEFENSE IN-DEPTH" MAS t'lET BEFORE THE END POINT RESULT COULD OCCUR,
DEMONSTRATION OF SUCCESS
- 0 WE PREPARE A TABLE OF ACCIDENT SEQUENCES AND DEMONSTRATE THAT "DEFENSE IN DEPTH" WAS MET FOR EACH, 0
WE INDICATE WHAT EQUIPMENT AND WHAT PROCEDURES WERE INVOLVED USING NUMBER AND LETTER CODES, 0
WE INCLUDE ALL SEQUENCES ABOVE A CUTOFF FREQUENCY, 0
WE INCLUDE AT LEAST 2 SEQUENCES FOR EVERY INITIATOR REGARDLESS OF FREQUENCY,
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PROPOSED TABULAR DISPLAY OF DEFENSE IN DEPTH DEFENSE IN DEPTH CONPONENT EVENT SEQUENCE EQUIPNENT 1
2 PROCEDURES 1
2 SEQUENCE 1 N,A, A
D N,A, SEQUENCE 2 N,A, N,A, N,A, N,A, SEQUENCE 5 C
E
- ETC, ALL SEQUENCES HAVING FREQUENCY
> 10
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OF TOTAL OF ALL SEQUENCES AND TOP 2 SEQUENCES OF EACH INITIATOR,
VERIFI CATI ON OF ANAlYSIS 0
THE FIDELITY OF NODELING OF PLANT SYSTENS WILL BE EXPLICITLY REPRESENTED IN THE IPE AND ITS SUPPORTING FILES, 0
THE ADEQUACY OF OUR PROCEDURES WILL BE DENONSTRATED BY OUR TRANSIENT ANAlYSIS OF PLANT RESPONSE AND VERIF ICATION THAT ASSUYiED OPERATOR ACTIONS WOULD BE REQUIRED BY PROCEDURES, 0
THE ADEQUACY OF OPERATOR TRAINING AND THEIR PERFORNANCE IN EXECUTING PROCEDURAL GUIDANCE MILL BE NEASURED BY WRITTEN TESTS OF OPERATOR KNOWLEDGE AND NEASURENENTS OF OPERATOR PERFORNANCE IN SINULATOR TRAINING FOR CONPARISON TO ANALYSIS ASSUMPTIONS.
NAINTAIN I NG THE ANALYSIS 0
AIL PLANT EQUIPNENT OR PROCEDURAL YiODIFICATIONS WILL BE REVIEWED TO DETERMINE INPACT ON SEQUENCE FREQUENCIES.
0 THE ANALYSIS MILL BE UPDATED ON A PERIODIC BASIS (FOR EXANPLE ON THE REFUELING CYCLE),
0 THE ANALYSIS WILL BE PROGRANMED FOR THE CONPUTER SO THAT RE-ANALYSIS MILL REQUIRE NINIMAL EFFORT 0
WE WILL CONTINUE TO DEVELOP NETHODS TO EXTEND THE CONPLETENESS OF THE ANALYSIS AT A REASONABLE LEVEL OF
- EFFORT, GREATER SUPPORT STATE DEFINITION LOSS OF INSTRUNENTATION INFLUENCE OF CREW SUBSTITUTIONS NORE DEFINITIVE EVALUATION OF SEVERE WEATHER EFFECTS
- ETC,
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SUNNARY p
gE FIR>LY FNDORSE A MODIFIED VERSION OF THE IDCOR BMR-I PE NETHODOLOGY, o
HE BELIEVE THAT ALL ACCIDENT SEQUENCES SHOULD BE INDIVIDUALLYCARRIED TO STABLE PLANT CONDITIONS, o
ANALYSIS ON THE BASIS OF INDIVIDUALSEQUENCES TO ASSURE EXPLOITATION OF ALL PLANT CAPABILITY HAS SHARPLY REDUCED CALCULATED PLANT DANAGE FREQUENCIES.
THE FUNDANENTAL REASON FOR THIS IS THAT "DEFENSE IN DEPTH" HAS BEEN ACHIEVED.
ME EXPECT SEQUENCES FOR MHICH "DEFENSE IN DEPTH" HAS NOT BEEN NET TO HAVE THE HIGHEST FREQUENCIES FOR ANY GIVEN INITIATOR o
THIS APPROACH OFFERS A LOGICAL AND CREDIBLE BASIS FOR ACHIEVING CLOSURE ON INTERNAL EVENT SEVERE ACCIDENTS,
RECOMNENDATIONS 0
PERFORM RESEARCH TO SUPPORT ESTABLISHMENT OF CORE/VESSEL STABILIZATION AND CORED DEBRIS/CONTAINMENT STABILIZATION CRITERIA 0
IMPLEMENT A PHASED APPROACH IN THE IPE GENERIC LETTER 0
REQUIRE THAT EACH ACCIDENT SEQUENCE BE CARRIED TO A STABLE STATE OR FAILURE 0
REQUIRE DEMONSTRATION OF DEFENSE IN DEPTH FOR DOMINANT SEQUENCES
OBSERVATIONS 0
TO ACCOMPLISH THE RECOMMENDED REQUIREMENTS A TRANSPARENT METHODOLOGY MUST BE USED 0
UTILITY PARTICIPATION IN THE IPE PROCESS SHOULD BE ENCOURAGED 0
INTERNAL UTILITY TRANSIENT ANALYSIS CAPABILITY IS HIGHLY DESIRABLE
Enclosure 2
DECEMBER 12, 1987 PP8,L BRIEFING ON IPE INSIGHTS NAME Paul Hill Ed Heckman Bruce Kenyon Michael B.
Detaman Gary L. Merrill W.
H. Rasin Larry Shao Ashok Thadani Richard Barrett S.
A. Varga M.
C. Thadani Tom Murley Mark Caruso John C.
Lane William Beckner James Norberq Cecil Thomas Wayne Hodges Glenn Kelly W. R. Butler Bruce Boger Franklin Coffman Ron Hernan AFFILIATION PPSL PPE(L PPSL PPE(L PPSL NUMARC NRR/DEST NRR/DEST NRR/DREP/RAB NRR NRR NRR NRR RES/SAIB RES/RHFB NRR/DEST NRR/PTSB NRR/DEST/SRXB NRR/DREP/RAB NRR/PDI-2 NRR/ADRI RES/RMFP NRR/PMAS
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