ML20206B171
| ML20206B171 | |
| Person / Time | |
|---|---|
| Issue date: | 08/13/1988 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-2589, NUDOCS 8811150359 | |
| Download: ML20206B171 (53) | |
Text
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i DATE ISSUED: 8/13/88 ACRS Subcomittee Meeting Sumary/ Minutes For the Severe Accidents July 13, 1988 Washington, D.C.
Purpose The ACRS Subcomittee on Severe Accidents met on July 13, 1988.
The purpose of this meeting was to discuss the staff's integration plan for closureofsevereaccidentissues(SECY-88-147). Copies of the agenda and selected slides from the presentation are attached.
The meeting began at 9:00 a.m. and adjourned at 4:20 p.m., and was held entirely in open session. The principal attendees were as follows:
Attendees ACRS NRC/RES W. Kerr, Chairman T. Speis C. Michelson, Member (p/t)
B. Sheron P. Shewmon, Member M. Cunningham C. Siess Member F. Eltawila D. Ward, Member C. Wylie, Member NRC/NRR I. Catton, Consultant L. Shao P. Davis, Consultant C. Thomas J. Lee, Consultant D. Houston, Staff Discussion The principal document for discussion at this meeting was SECY-88-147, "Integration Plan For Closure of Severe Accident Issues," dated May 25, 1988. The NRC staff had previously discussed this document with the Camiissioners on June 2,1988.
Copies of the document and excerpts from MQg fjj jgjp 880013 T589 PNU
'+
7 i
1 Severe Accidents Meeting Minutes July 13, 1988 i
r the transcript of the Comiss'on meeting were provided to the Subcommit-tet Members and Consultants prior to this meeting.
In his opening remarks, W. Kerr comended the staff for working toward
[
an integration plan but indicated that the plan, as written, was more a listing and description of those severe accident issues and programs that thould be jntegrated. He indicated that it appeared the inte-gration was yet to be fonnulated.
I T.Speis(RES)discussedthesevereaccidentintegrationplan,its l
purpose, objectives and elements. He stated that the cardinal part of this plan was to define the issues and their inter-relationships and to
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structure a research program to address these issues. He briefly described the current state of technology in regard to past studies and real accidents, risk significant sequences, severe accident research, containment loads / performance, source terms, regulations and outstanding issues. He gave some details for the study of containment loads and relative probabilities of failure modes for the general containment types. He also briefly discussed the severe accident research programs.
B. Sheron (RES) discussed the proposed generic letter for Individual PlantExaminations(IPEs). He discussed the major changer made to the
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letter since the last Subcommittee review of the proposed generic letter f
in April 1988. One major change was that no major containment modifica-
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tions would be required until the infonnation associated with generic f
issues which affect containment performance had been developed by the staff. Another key change in the letter was the emphasized request that each licensee use its staff to the maximum extent possible in r7nducting l
tha IPE.
He discussed the methods of analysis for the IPE and the 1
benefits of voing a PRA or ISAP. While the staff believes the PRA or ISAP is the preferred route to go, they will not make it a requirement.
In a 50.54(f) letter, the information requested can be specified but i
i 1
Severe Accidents Meeting Minutes July 13, 1988 the methodology can not. The staff is preparing a review document which provides guidance for reviewing IPEs.
This document will be discussed with CRGR and ACRS at future meetings and with utilities, industry and the public at a future workshop. Based on comments received, the document will be revised and then issued in final form. The schedule for utility response and participation will not start until the final document is issued.
M.Cunningham(RES)presentedanoverviewoftheeffortsunderwayto develop a final NUREG-1150.
He briefly discussed the objectives of and improvements in the final report. He discussed the role of expert judgment, process for use of experts and the composition of panels. He injicated that 10 source term code package (STCP) runs had been per-formed per plant versus 6 runs for the draft analysis. External events would be treated in the analysis of Surry and Peach Bottom.
The LaSalle (RMIEP) study would not be finished until next fiscal year with the Babcock and Wilcox and Combustion Engineering plant analyses in two years or so.
L. Shao (NRR) briefly discussed the activities of the External Events Steering Group. The Group is coordinating efforts between the NRR/RES staff and NUMARC. Methodology for the treatment of external events is expected in about 18 months.
C. Thomas (NRR) briefly discussed the current status of ISAP !!. He indicated that 12% of the utilities had expressed an interest in partic-ipating in ISAP !! while 34% were not interested and the remainder were undecided. He stated that the IDCOR IPEM would not be suitable for ISAP.
T. Speis closed with a discussion of the severe accident closure pro-cess. This involved the completion of an IPE including improvements as appropriate, a commitment to develop and implement a framework for an
s e,
Severe Accidents Meeting Minutes July 13, 1988 accident management program and the implemention of generic requirements from the containment performance improvements program.
During the presentation. Subcommittee Members and Consultants extensive-ly discussed the staff's integration plan for closure of severe accident issues and the individual activities that fell within the plan.
The following topics were pursued during the discussion (random order):
(1) _ Containment performance - The staff was asked what is the measure of containment performance.
If it is to be improved as indicated, how will these improvements be judged.
(2) Direct Containment Heating - Various concerns were expressed about the staff's treatment of direct containment heating, e.g. the assumptions made about 100% molten core discharge or the phenomena of melt expulsion occurring at all. The research program does not i
appear to be addressing this properly.
The conclusion of the Xouts' report was discussed, that is, the expected resolution based on research is many years away, therefore, the probability of DCH should be made low by hardware changes or procedural measures.
(3)
External Initiators - The analysis with the treatment of externai initiators should be performed now and not be delayed for another 11-2 years.
The staff appears to have overlooked the significance of these events for the IPE program. They have been shown to be major contributors to risk in previous PRAs.
(4)
NUREG-1150 - Concerns were expressed about the suitability of applying certain codes and models beyond the reactor conditions for which they were developed or validated. Also, the makeup of the expert panels was questioned and it would appear that certain experts were neither considered or consulted.
I t was strongly
- 6 Severe Accidents Meeting Minutes July 13, 1988 i
l suggested that the final version of NUREG-1150 be peer reviewed as I
part of the process to establish credibility.
i (5) Definitions - The staff was asked to provide better definition or guidance in many years. Specifically, definitions were asked for j
terms such as: Severe Accident, Damaged Core, Core Damage, Core Melt Yulnerabilities, Large Radioactive Release, Containment Performance Containment Failure, and Containment Bypass.
NOTE:
Additional meeting details can be obtaii'ed from a transcript of this meeting available in the NRC Pubiic Document Room, 1717 H Street, N.W., Washington, D.C., or can be purchased from Heritage Reporting Corporation, 1220 L Street, N.W.,
l Suite 600, Washington, D.C. 20005,(202)628-4888.
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_ _ _ _ _ _ _..,,, _,. _ _ _ _ _ _, _.. _. - - -.. _. ~. _. _ _ _... _ _. - _. _, _,. -,.. _. _.... _ -
ACRS Severe Accidents Subcomittee Meeting July 13, 1988 Washington, D.C.
- Tentative Presentation Schedule -
Ir tegration Plan For Closure
~ f Severe Accident Issues o
A.
Subcomittee Chaiman Renarks W. Kerr, ACRS J:00 a.m.
B.
Discussion of SECY-88-147 T. Speis, RES 9:15 a.m.
et. al.
(Spw))
- Introduction and State of Technology
- Individual Plant Examinations (JYeM)
- Containment Perfomance Improvements [Jp' /d
- ' 7 :::d "!:-t ^ : :t': :
r
- BREAX ***
10:45-11:00 a.m.
- SevereAccidentResearchProgran[J/'#4)
- Accident Management h/M
- NUREG-1150, Reactor Risk Reference ((m44MJ #4)
Document 9
' Generic Safety Issues h W E d
"* LUNCH ***
12:30- 1:15 p.m.
(Resume Discussion)
T. Speis, RES h W)
- External Events
- Integretted Safety Assessment Program (mea 7h
- 'ft:: ::d ":::t: :
- SafetyGoalPolicy(8pir) i
/
C.
General Discussion and Plans for All 2:30 p.m.
Comittee Presentation (7/14/88)
D.
Adjourn 3:00 p.m.
l
~.-
k ACRS SEVERE ACCIDENTS SUBC0f'fi!TTEE BRIEFING ON SEVERE ACCIDENT INTEGRATION PLAN THEMIS P. SPEIS 301/492-3710 l
0FFICE OF NUCLEAR REGULATORY R U.S. NUCLEAR REGULATORY COMMISS JULY 13, 1988 l
6 l
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D SEVERE ACCIDENT INTEGRATED PLAN 1
EU_R_P.Q1g:
TO PRESENT STAFF'S PLAN FOR INTEGRATION P
o AND CLOSURE OF SEVERE ACCIDENT ISSUES o
Q W TIVESi TO PROVIDE AN UNDERSTANDING OF THE STAFF ACTIVITIES THAT ARE UNDER WAY TO IMPLEMENT THE COMMISSION'S SEVERE l
ACCIDENT POLICY l
TO ASSURE THAT THESE ACTIVITIES ARE l
l-CONSISTENT WITH THE COMMISSION,'S POLICY AND STRATEGIC G0ALS I
TO ASSURE THAT Tile STAFF ACTIVITIES ARE i
CONSISTENT AMONG THEMSELVES, HAVE A COMMON GOAL OF ULTIMATELY LEADING TO l
IMPROVED PLANT SAFETY, AND ARE PPOPERLY
(
COORDINATED AMONG THE RESPONSIBLE NRC ORGANIZATIONS f
TO ASSURE THAT THE COMMISSION IS AWARE OF THE KEY TECHNICAL AND POLICY ISSUES, SOME j
OF WHICH WILL NEED COMMISSION GUIDANCE OR APPROVAL l
l TO DESCRIBE TllE USE OF SAFETY G0ALS AND j
l BACKFIT POLICY IN THE CLOSURE PROCESS 1
i f
i
SEVERE ACCIDENT ACTIVITIES o
INDIVIDUAL PLANT EXAMINATIONS (IPE) o CONTAINMENT PERFORMANCE IMPROVEMENTS (CPI) o IMPROVED PLANT OPERATIONS (IPO) o SEVERE ACCIDENT RESEARCH PROGRAM (SARP) o ACCIDENT MANAGEMENT (AM) PROGRAM o
GENERIC SAFETY ISSUES o
EXTERNAL EVENTS o
INTEGRATED SAFETY ASSESSMENT PROGRAM (ISAP) o SEVERE ACCIDENT POLICY FOR FUTUP.E PLANTS o
SEVERE ACCIDENT CLOSURE /USE OF SAFETY G0AL 1
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STATE OF TECHNOLOGY o
WASH-1400, OTHER PRA'S, TMI-2 AND CHERNOBYL ACCIDENTS, ALL i
TELL US THAT SEVERE ACCIDENTS REPRESENT THE MAJOR CONTRIBUTION TO RISK FROM COMMERCIAL NUCLEAR POWER PLANTS 0
IDENTIFICATION OF RISK SIGNIFICANT SEQUENCES (PRA'S, OPERATIONAL EXPERIENCE) i o
SEVERE ACCIDENT RESEARCH EXPERIMENTS MODEL DEVELOPMENT i
4 o
CONTAINMENT LOADS / PERFORMANCE A GOOD UNDERSTANDING OF SEVERE ACCIDENT CHAll.ENGES TO CONW"'"CTL tFC f 'S; CC1'S)
A GOOD UNDERSTANDING OF CONTAINMENT PERFORMANCE l
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SOURCE TERMS t
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SEVERE ACCIDENT REGULATIONS IMPLEMENTED
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OUTSTANDING ISSUES t
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y penetortiora
.1 EFFECT OF LOSSES AND TIMING, LOW F5~C5NAliO~
CO.MPARIS_ON_ CALCULATION C_ONDITIONS _. _
Sinks pre-heating of w50 psi for ~300 min 100 i
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100% Quench in 1-min
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Results biased to hatched area 100% Quench in 80-min N
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EFFECT OF LOSSESo HIGH P SCENARIO COMPARISON. CALCULATION CONDITIONS ~ ~ ~
Sinks pre-heeting at ~!io psi for ~300 min (TMLB)
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Note: Direct heating of containment r+:nosphere not taken into account.
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CORE FR ACTtON TO DIRECT HEATING (with oxidaMon) l l
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SP-2 pressure and temperatu.~e ss a funetten of core fraatten involved in dir6ct heating (with metal oxidation)
1 TABLE 1 FAILURE MODES IN LARGE DRY AND SUBATMOSPHERIC CONTAINMENTS Relatb0 Probability Failure Mode of Occurrence Steam Explosion: Miss%i Very Low Varial:le Failure to isolate
- Hydrogen Bum / Detonation Low l
Overpressurization: Early(Due to Steam Spike)
Low Overpressurization: Eaiy (Direct Heating)
Variable **
Overpressurization: Late (Over 8 Hrs.)
High Medium Basemat Melt-Through laterfacing LOCA: (Containmerit Bypass)*
Variable l
- Mitigation Features are ineffecdve Against These Failures. Their Probability Can Be Reduced by Precedural/ Design Changes
" Geoir.ary Dependent Aba Wde Range of Views on Phenomena and Consequens~.es I
l
TABLE 2 FAILURE MODES IN MARK i AND ll CONTAINMENTS Relative Probability j
Failure Mode of Occurrence l
Steam Explosion: Missile Very Low Failure to isolate
- Variable l
Hydrogen Bum / Detonation Very Low i
(Inerted Containment)
Overpressurization: Early(Due to Steam Spike)
Low i
Overpressuiustion: Earfy (Corium/Ccncrete Interaction Plus Steam)
High Overtemperature: carty (Corium/ Concrete l
Interaction)
High Steel Containment Melt-Through Variable ** (Applies to Mark-1 Only)
Interfacing LOCA: (Containment Bypass)*
Variable i
I
- Mi4^Jan Features are ineffectwo A0einst These Failures. Their Probability Can Be Reduced ty l
Procedural / Design Changes
" Depends on Conum's Ability to Flow to ard Melt Through the Uner 1
TABLE 3 FAILURE MODES IN A MARK-ill CONTAINMENT l
Relative Probability I
Failure Mode of Occurrence i
h i
Steam Explosion: Missile Very Low Failure to isolate
- Variable l
Hydrogen Bum / Detonation High (Standing Flames; From Station Blackout Sequences) l Overpressurization: Early (Corium/ConcreteInteraction)
Medium i
Interfacing LOCA:
l (Containment Bypass)*
Variable Mitigation Features are ineffective Against Thess Failures. The:r ProbabiEty Can Be Reduced by Procedural / Design Changes l
4
.-----,e--
1 TABLE 4 FAILURE MODES IN AN ICE CONDENSER CONTAINMENT Relative Probability Failure Mode of Occurrence Steam Explosion: Missile Very Low Failure to isolate
- Variable Hydrogen Bum / Detonation: Early H'gh (For Black-Out SequencesWhere Power to Igniters and Air Retum Fans is Lost)
Overpressurization: Early (Due to Steam Spike)
Low Overpresstrization: Early (Direct Heating)
Variable **
Overpressurization: Late (Over 8 Hrs.)
High Basemat Melt-Through Medium Interfacing LOCA: (Containment Bypass)*
Variable
- Mitigation Features are ineffective Against These Failures. Their Probability Can Be Reduced by Procedural / Design Changes
" Geometry Dependent; Also Wide Range of Vievrs on Fhersmene and Consequences
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I CONTAINMENT BUILDINGS l
DESIGNED FOR:
DBAs (E.G., LOCA/SLB TEMPERAit'RES 4 PRESSURES) l EXTERNAL EVENTS (EARTHOUAKES, FLCODS, TORNADOES)
TID-14844 FIS$10N PRO')UCT SOURCE TERM (RADI ATION:
i RQ S.A. P/T EFFECTS)
USE, OF CONSERVATIVE C01'ES/ STANDARDS l
MARGINS (AVAILABLE) ABOVE DESI6N LEVELS:
MARGINS ARE CONTAINMENT SPECIFIC (V0lli.'d, MATER'ALS, CONFIGURATIONS, ETC.;
IN f;ENERAL, STUDIES (EXPERIM/ ANALYTICAL) HAVE INDICATED THAT CONTAINMENT SYSTEMS CAN SURYlVE PRESSURE CHALLENGES OF 2.5 TO 3 TIMES DESIGN r
LEVELS RESIDUAL CHALLENGES FROM SEVERE ACCIDENTS:
l i
FOR EACH CONTAINMENT TYPE THERE REMAIN FAl'.URE l
l MECHANISMS WHICH COULD LEAD TO CONTAINMEPII I
FAILURE l
I i
KEY QUESTIONS:
(1) REASONABLE UNDERSTANDING l
0F CHALLENGES TO CONTAINMENTS (LOADS (P.T.),
l MARGINS AVAILABLE, FAILURE MODES (TIME,
(
LOCATION), (2) REASONABLE UNDERSTANDING OF f
PROBABILITIES (E.G., SOME FAILURE MODES, GIVEN
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A S.A., ARE MORE PROBABLE THAN OTHERS) r l
.i
l RANGE
- OF QWTAff90rr DESIM Af0 CAPABILITY IPESSURE ESTimTES URTAlff0fTTYPE PRESSURE RAME DESI@ N PKE LARGE DRY 95 - 150 PSIG 6 - 60 PSIG StEATIOSPERIC 120 - Ito PSIG R5PSIG I& 0)MDENSER 60 - 120 PSIG 12 - 15 PSIG mit:I 120 - 180 PSIG 60 - 65 PSIG MPK II 135 - 150 PSIG 6 - 55 PSIG m RK III 00 - 100 PSIG 15 PSIG
- RANGES IEFLECT BOTH IMERTAlffTTES ABOUT FAILIFE M]DFS AND DIFFEREPES IN DES!98 DETAILS FOR TE SWE CWTAI!WUfT TYE.
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CONTAINMENT PERFORMANCE IMPROVEMENIS o
SOME CONTAINMENTS POTENTIALLY VULNERABLE TO EARLY FAILURE DURING SEVERE ACCIDENT (DRAFT NUREG-1150) o EVALUATING GENERIC CHALLENGES, FAILURE MODES a POTENTIAL IMPROVEMENTS o
STATUS FOR MARK is:
APPROACH BEING PURSUED INVOLVES BOTH ACJ1 DENT PREVENTION AND MITIGATION ADDITIONAL SOURCES OF WATER BEING EXPLORED FOR CORE COOLING, CONTAINMENT AND DEBRIS COOLING, AND FISSION PRODUCT SCRUBBING ADS RELIABILITY ENHANCEMENT VENTING UTILIZING SUPPRESSION POOL FOR SCRUBBING USEFUL, BUT DOWNSIDES SHOULD BE MINIM! ZED REGULATORY ANALYSES OF ABOVE BEING PERFORMED o
MARK ! IATERIM AND FINAL RECOMMENDATIONS DUE TO COMMISSION BY JULY AND FALL OF '88, RESPECTIVELY l
0 RECOMMENDATIONS FOR OTHER CONTAINMENT TYPES DUE TO l
COMMISSION BY FALL '89 L
.~
SUMf1ARY 0F FEB. 24-26, 1988 BWR MARK 1 WORKSHOP THREE-DAY MEETING WITH 150 INDUSTRY, RESEARCHER, STAFF AND PUBLIC REPRESENTAllVES INDUSTRY Et1PHASIS ON PREVENTION.
ANY FIXES SHOULD BE PLANT SPECIFIC FROM IPE.
VARIETY OF VIEWS ON PROBABillTY OF LINER MELT-THROUGH MANNER.0F VESSEL FAILURE AND RELEASE OF DEBRIS IliPORTANT INDUSTRY BEllEVES WATER CAN PREVENT LINER MELT-THROUGH WATER BENEFICIAL, BUT NO CONSENSUS FROM NRC RESEARCHERS ON WHETKdR LINER FAILS AND WHEN GENERAL AGREEMENT--WATER IN DRYWELL USEFUL TO DELAY /
PREVENT SHELL FAILURE AND TO REDUCE FISSION PRODUCT P.ELEASES AGREEMENT THAT ADS RELI ABILITY litPORTANT.
IllPROVEMENTS ACHIEVABLE AT ';0 DEST COST.
SUSOUEHANNA LICENSEE TAKING ACTIONS NOW.
POTENTIAL POSITIVE AND NEGATIVE SAFETY IMPACTS OF VENT!?jG REDUCE CORE-MELT LIKEllH00D, REDUCE CONSEQUENCES, BUY TIME POTENTIAL FOR UNNECES9ARY RELEASE, INCREASE CORE-MELT LIKEllH00D FOR SOME SEQUENCES MORE FOCUSED RESEARCH NEEDED ON VESSEL FAILURE AND DEBRIS RELEASE VESSEL FAILURE CHAP.ACTERISTICS AND LIKEllH00D OF LINER MELT-THROUGH WITH WATER
~
FAILUE P0 DES IN l
MARK I C0hTAlttDUS ELATIVE Pf0BABILITY FAILUE PGE T_QQQEggE f
l 0.
(NERPESSURIZATION: (NEPPESSURIZATION HIGi+
LEAD!t0 TO COPE DIFAGE (1.E., C0tHAltf G T FAILUE EEF0E COE ELTING) l 1.
STEIN EXPLOSION:
MISS!LE VERY LO4 2.
FAILUE T0 ISOLATE
- VARIABLE 3.
HiDROGBi BURN /DETCtGTION VERY LOW 14.
CNERPESSL'RIZATION: EARLY (CORllM/CONCPETE H!G1 IfiTEPACTION PLUS STEN 1) 5.
06TDPEPATUE: EAPLY (CORilN/CONCETE HIGH f
INTEFACTim) 6.
STEEL C0tRAlttW ELT-THPOUGi VARIABLE" I
l i
l 7.
INTERFACING l.0CA:
(C0tJAI M NT BiPASS)*
VARIABLE l
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'MITIGAT!W FEATUES AE INEFFECTIVE AGAINST THESE FAlu) PES. TIEIR
~
PFOBABILITY CAN BE EDUED BY Pf0CEDURAL/ DESIGN OlATIS "DEPDOS ON CORllM'S ABILITY TO FLW TO Ato ELT ThTOUGH TIE LINER
+1R TIE ABSENCE OF WETWELL VDiTING i
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SEVERE ACCIDENT RESEARCH BEGINNING IN 1980, AFTER THE TMI-2 EVENT, RESEARCH HAS PROVIDED A DATA BASE AND MODELS FOR:
o FISSION PRODUCT RELEASE, TRANSPORT, DEPOSITION, 4 REVAPORIZATION o
CONTAINMENT LOADING BY HIGH PRESSUPE MELT EJECTION (HPE) o HYDROGEN DETONATION AND BURNING o
CORE / CONCRETE ISTERACTIONS (CCl) o CONTAINMENT PERFORMANCE TESTING o
EFFECTS OF NATURAL CIRCULATION ON THE PRIMARY SYSTEM o
CORE MELT PREGRESSION (EARLY OTAGES) 1 FUTURE RESEARCH EFFORTS WILL FOCUS ON SPECIFIC ISSUES SUCH AS:
o CONTAINMENT FAILURE PROBABILITY BY DIRECT CONTAINMENT HEAT!NG (DCH) INCLUDING EFFECT OF NATURAL CIRCULATION o
MELT SPREADING AND POTENTIAL CONTAINMENT SHELL FAILURE IN MARK !s o
RESEARCH DATA AND MODELS TO ASSESS ACCIDENT MANAGEMENT STRATEGIES l
l o
LONGER TERM CONF!RMATORY RESEARCH ON:
l l
DCH CONSEQUENCES REFINEMENT OF HYROGEN BEHAVIOR MODELS CORE MELT PROGRESSION (LATE STAGES)
CORE / CONCRETE INTERACTIONS FURTHER MODEL ASSESSMENT AND REFINEMENTS l
t l
AN EXAMPLE OF AN ISSUE AND ITS l
l ASSOCIATED NEAR AND LONG-TERM RESEARCH CONTA! MENT TYPE LARGE DRY PWR i
l ASSOCIATED ISSUES o
POTENTIAL CONTAINMENT FAILURE MODES
[
DIRECT CONTAINKENT I
l HEATING (DCH)
HYDROGEN BURN / DETONATIONS LATE FAILURE BY CCI LOADS i
(OVER TtP) o CONTAINMENT PERFORf!ANCE t
o ACCIDENT MANAGEMENT iTRATEGIES DEPRESSURIZATION OF PRIMARY SYSTEM l
RESEARCH TO ADDRESS ISSUE i
o DCH PROBABILITY OF HIGH PRESSURE MELT EJECTION (NATURAL CIRCULATION)
CUT 0FF PRESSURE FOR HPE MANAGEMENT THROUCH DEPRESSURIZATIO':
CONSEQUENCES
t CONTA I NMENT PEFORMANCE FOCUSED RESEARCH PWR BWR BWR BWR LARGE DRY MARK I j._Il MARK Ill ICE CONDENSEI MAJOR RELATED MAJOR RELATED MAJOR RELATED MAJOR LES ISSUES RESEARCH ISSUES RESEARCH ISSUES RESEARCH ISSUES
- RES CIRECT PROBABILITY SHELL MELT MELT SPREADING HYDROGEN ASSESS COMBUSTION HYDROGEN CONTAINMENT (NATURAL CIRC.)
THROUGH TESTS BURNS &
CODES WITH EXISTING BURNS SAME HEATING (DCH)
MARK-I ONLY DETONATIONS DATA AS MARK-III (EARLY)
CUTOFF PRESSURE (EARLY)
HEAT TRANSFER (EARLY)
TO LihER TESTS DCH - SAME MANAGEMENT AS PWR LARGE (DEPRESSURIZATION)
MELT SPREADIMG DRY (EARLY)
USING VARIOUS CUNSEQUENCES CORE DEBRIS (SURTSEY TESTS)
MODEL COMPLETION INITIAL CONDS.
(MELT PROGRESSION)
INITI AL CONDS.
(MELT PROGRESSION)
OVERPRESSURE LARGE-SCALE OVE2 TEMP.
CCI TESTS OVER PST MANAGEMENT OVER PET MANAGEMENT OVER P&T (LATE FAILURE)
SAME AS PWR FRG BETA TESTS IARGE DRY (DRYWELL) lap 4~
)RY LARGE DRY ON CCf (EARLY FAILURE)
(EARtV-LATE)
(LATE FA: LURE)
IMPROVE & ASSESS CCI CODES INITI AL CONDS.
(MELT PROGRESSION)
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t ACRS MEETING ON THE IMPLEMENTATION PLAN OF THE SEVERE ACCIDENT POLICY STATEMENT INDIVIDUAL PLANT EXAMINATIONS THEMIS SPEIS, DEPUTY DIRECTOR OFFICE OF NUCLEAR REGULATORY RESEARCH BRIAN SHERON, DIRECTOR DIVISION OF SYSTEMS RESEARCH OFFICE OF NUCLEAR REGULATORY RESEARCH JULY 13,1908 l
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SUMMARY
- STAFF HAS DEVELOPED GENERIC LETTER TO INDUSTRY TO IMPLEMENT THE SEVERE ACCIDENT POLICY FOR OPERATING REACTORS
- STAFF REVIEW OF THE IDCOR METHODS FOR CONDUCTING THE INDIVIDUAL PLANT EXAMINATION HAS BEEN COMPLETED
- STAFF HAS INTERACTED FREQUENTLY WITH THE ACRS DURING THE DEVELOPMENT OF THE GENERIC LETTER AND DURING THE STAFF'S REVIEW OF THE IDCOR METHODS
- PROPOSED GENERIC LETTER WAS EXTENSIVELY REVIEWED BY THE CRGR
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SUMMARY
(CONT.)
DU"ING OUR INTERACTIONS ON THE IMPLEMENTATION PLAN OF THE SEVERE ACCIDENT POLICY WE DISCUSSED THE FOLLOWING
- EXAMINATION PROCESS AND METHODS
- STAFF'S PLAN TO ADDRESS SEVERE ACCIDENTS FROM EXTERNAL EVENTS
- ROLE OF SEVERE ACCIDENT MANAGEMENT
- PROPOSED STAFF POSITION TO RESOLVE USI A-45
- PROPOSED STAFF PLAN TO REVIEW IPE SUBMITTALS AND SCHEDULE
- DISCUSSION ON THE STAFF USE OF THE IPE RESULTS
- CONCLUDING REMARKS WE PLAN TO PERIODICALLY INFORM THE ACRS, CRGR AND THE COMMISSION ON THE PROGRESS OF THIS TASK 4
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SUMMA 3Y (CONT.)
- WE HAVE SPENT SUBSTANTIAL EFFORTS IN DEVELOPING THE GENERIC LETTER AND THE SUPPORTING DOCUMENTS.
WE BELIEVE THAT UTILITIES CAN PROCEED TO PERFORM THE IPEs AND TO FURTHER ENHANCE SAFETY WHERE APPROPRIATE
- AT THE MAY 5,1988 ACRS MEETING, NUMARC STATED THAT INDUSTRY UNDERSTANDS THE OBJECTIVES OF THE IPEs, HAS SUFFICIENT KNOWLEDGE OF THE STAFF'S WORK ON THE IPE, AND URGES THE NRC TO ISSUE THE GENERIC LETTER SG UTILITIES CAN PROCEED TO PERF0IiM THEIR IPEs e
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- 4. EXAYINATION PROCESS l
LICENSEE'S STAFF SHOULD PARTICIPATE IN ALL ASPECTS OF THE IPE SO THAT KNOWLEDGE GAINED BECOMES AN INTEGRAL PART OF OPERATING, TRAINING AND PROCEDURE PROGRAM LICENSEES SHOULD CONDUCT SYSTEMATIC EXAMINATION OF PLANT DESIGN, OPERATION, MAINTENANCE AND E.MERGENCY OPERATION TO:
- IDENTIFY PLANT SPECIFIC VULNERABILITIES (DESIGN AND PROCEDURAL) TO SEVERE ACCIDENTS (FOR BOTH CORE DAMAGE AND CONTAINMENT PERFORMANCE); BOTH INTERNAL AND EXTERNAL INITIATORS ARE TO BE CONSIDERED.
EXTERNAL INITIATORS WILL BE CONSIDERED SEPARATE FROM THE IPEs AND ON A LATER SCHEDULE 8
EXAEXATION PROCESS (CONT.)
- UNDERSTAND THE SEQUENCES THAT CONTRIBUTE THE MOST TO THE TOTAL CORE DAMAGE OR TO POOR CONTAINMENT PERFORMANCE UNDERSTAND WHAT COULD PROBABLY GO a
WRONG IN A PLANT IDENTIFY AND EVALUATE MEANS FOR IMPROVING PLANT / CONTAINMENT PERFORMANCE (VIA HARDWARE ADDITIONS / MODIFICATIONS, ADDITION TO PROCEDURES, TRAINING)
DECIDE WHICH IMPROVEMENTS WILL BE IMPLEMENTED AND SCHEDULE FOR IMPLEMENTATION i
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- 6. BENEFITS OF P3A LICENSE RENEWALS
- PRA COULD BE A BASIS TO IDENTIFY RISK-SIGNIFICANT COMPONENTS AND SYSTEMS THAT SHOULD BE MAINTAINED AT AN ACCEPTABLE LEVEL OF RELIABILITY DURING THE LICENSF RENEWAL PERIOD RISK MANAGEMENT
- RISK MANAGEMENT PROGRAM THAT CONTINUALLY ASSESSES THE SAFETY OF THE PLANT PROVIDES A POWERFUL TOOL TO THE PLANT MANAGEMENT SUPPORT FOR LICENSING ACTIONS
- PRA MIGHT BE USED TO JUSTIFY TECHNICAL SPECIFICATION CHANGES INTEGRATED SAFETY ASSESSEMENT PROGRAM
= OPTIMIZES THE TOTAL SAFETY AND EXPEDITES SCHEDULE TO IMPLEMENT FIXES 1
- 7. ROLE OF ACCIDENT MANAGEMENT
- ACCIDENT MANAGEMENT IS A PROCESS IN WHICH ACTIONS THAT CAN PREVENT CORE DAMAGE OR MITIGATE THE CONSEQUENCES OF A SEVERE ACCIDENT ARE IDENTIFIED, EVALUATED, INCORPORATED INTO A STRUCTURED PROGRAM, l
IMPLEMENTED AT A PLANT SITE AND ARE AVAILABLE TO THE OPERATORS AND PLANT MANAGEMENT IN THE EVENT OF AN ACCIDENT
- ACCIDENT MANAGEMENT ENCOMPASSES HARDWARE, HUMAN, AND ORGANIZATIONAL FACTORS
- IT PROVIDES DECISION MAKERS AT THE PLANT A STRUCTURED PROGRAM FOR MANAGING ACCIDENTS, INCLUDING SEVERE ACCIDENTS
- STAFF AND NUMARC DISCUSSING SCOPE AND SCHEDULE FOR DEVELOPMENT OF SEVERE ACCIDENT MANAGEMENT PROGRAM l
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ACCDENT MANAGEYENT (CONT)
- PROPOSED GENERl'C LETTER ADDRESSES ACCIDENT MANAGEMENT AS FOLLOWS:
- UTILITIES ARE EXPECTED TO ULTIMATELY DEVELOP A STRUCTURED, COMPREHENSIVE ACCIDENT MANAGEMENT PROGRAM FOR PREVENTION OR MITIGATION OF RISK IMPORTANT SEVERE ACCIDENTS
- WHILE A FORMAL ACCIDENT MANAGEMENT PROGRAM MAY BE UNDER DEVELOPMENT WHILE THE IPE'S ARE BEING CONDUCTED, UTILITIES ARE EXPECTED TO IDENTIFY MEASURES THAT PLANT PESONNEL CAN AND SHOULD TAKE TO PREVENT / MITIGATE RISK IMPORTANT SEVERE ACCIDENTS.
ASSESS AGAINST THE CRITERIA 0F 10 CFR 50.59 AND IF APPROPRIATE, SUBMIT FOR NRC REVIEW IN ACCORDANCE WITH 10 CFR 50.90 a
- 8. RELATIONSHIP TO USIs & GSIs USI A-45 ANALYSES HAVE SHOWN THAT DECAY HEAT REMOVAL FUNCTION FAILURES ARE SUFFICIENTLY PLANT SPECIFIC AND WOULD REQUIRE SYSTEMATIC EXAMINATION PROPOSED STAFF RESOLUTION OF A-45 IS TO SUBSUME ISSUE INTO IPEs THE PROPOSED GENERIC LETTER STATES THAT THE IPE SHOULD ENSURE THAT THE VULNERABLE ASPECTS OF DHR FUNCTION ARE IDENTIFIED THE PROPOSED GENERIC LETTER PROVIDES INSIGHTS GAINED FROM SIX LIMITED SCOPE PRAs PERFORMED BY NRC UNDER THE A-45 PROGRAM FOR OTHER USIs & GSIs e
- IF IPE IDENTIFIES ANY VULNERABILITIES THAT ARE TYPICALLY ASSOCIATED WITH A USI OR GSI AND UTILITY PROPOSES A MEASURES ACCEPTABLE TO THE STAFF TO ELIMINATE OR SUBSTANTIALLY REDUCE THE VULNERABILITY, OR
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- 9. COMMENTS OX ACPS LETTER DATED MAY 10, 1988
- ACRS RECOMMENDED BROADEN SCOPE OF IPE AND REQUIRE EACH LlCENSEE TO CONDUCT LEVEL-2 PRA TO SUBSUME ALL OUTSTAN, DING NAFETY ISSUES (USIs/GSIs)
- ACRS ALSO RECOMMENDED TREATMENT OF BOTH IN'"ERNAL AND EXTERNAL INITIATORS AT THIS TIME
- THE STAFF SHARES ACRS VIEWS THAT A PROGRAM THAT INTEGRATES A NUMBER OF ONGOING REGULATORY ACTIVITIES IS DESIRABLE.
HOWEVER, IT IS INAPPROPRIATE TO IMPLEMENT SUCH PRGRAM AT THIS TIME:
- THE IDCOR IPEMs DEVELOPED BY INDUSTRY IN RESPONSE TO THE 1985 SEVERE ACCIDENT POLICY STATEMENT WAS FOUND (SUBJECT TO STAFF'S ENHANCEMENT) TO SATISFY THE INTENT OF THAT POLICY STATEMENT. WE HAVE NO BASIS FOR NOT ALLOWING USE OF THE IDCOR IPEMs 1
COMMENTS ON ACRS LETTER (CONT.)
- THE GENERIC LETTER DOES NOT DISCOURAGE, IN FACT ENCOURAGES, UTILITIES TO PERFORM PRAs AND WHERE APPROPRIATE THE STAFF MAY ALLOW MORE TIME FOR UTILITIES WHO ELECT TO PERFORM PRAs
- UTILITIES ARE ADVISED THAT IN THE FUTURE 1
THEY WILL BE EXPECTED TO EXAMINE AND IDENTIFY VULNERABILITIES TO SEVERE ACCIDENT DUE TO EXTERNALLY INITIATED
- EVENTS, INTEGRATION OF ONGOING ACTIVITIES INVOLVING EXTERNAL EVENTS MUST BE DONE TO PRECLUDE DUPLICATION OF EFFORTS
- IT IS UNLIKELY THAT ANY PLANT 4
MODIFICATION DUE TO INTERNAL EVENT 1
INITIATORS WILL RENDER THE PLANT MORE VULNERABLE TO EXTERNAL EVENT INITIATORS
- 10. CONCLUSIONS
- DEVELOPED GUIDANCE TO ENABLE UTILITIES TO PERFORM THEIR IPEs AND GAIN INSIGHTS ON ALL PLANT SYSTEMS AND COMPONENTS THAT COULD BE USED TO PREVENT CORE DAMAGE ACCIDENTS
- FOCUS UTILITIES' ATTENTION ON THE KEY EVENTS AND PHENOMENA AFFECTING THE PLANT IN GENERAL AND THE CONTAINMENT IN PARTICULAR
- DE-EMPHASIZING HEAVY RELIANCE ON BOTTOM LINE NUMBERS.
EMPHASIZING THE IDENTIFICATION AND IMPLEMENTATION OF RECOVERY PROCEDURES AND ACCIDENT MANAGEMENT PROGRAM
- NO MAJOR CONTAINMENT MODIFICATIONS REQUIRED UNTIL THE INFORMATION ASSOCIATED WITH GENERIC ISSUES WHICH AFFECT CONTAINMENT PERFORMANCE HAS BEEN DEVELOPED BY THE STAFF
= NO DUPLICATION OF EFFORTS BY INDUSTRY:
SUBSUMING A-45 RESOLUTION IN THE IPE AND SEPARATING TREATMENT OF EXTERNAL EVENTS AT THIS TIME
- WE RECOMMEND COMMISSION APPROVAL TO ISSUE THE GENERIC LETTER 1
NUREG-1150:
A STATUS REPORT PRESENTED TO ACRS JULY 13, 1988 JOSEPH A.
MURPHY OFFICE OF NUCLEAR REGULATORY RESEARCH U. S. NUCLEAR REGULATORY COMMISSION
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- Dreaft NUREG-1150 published for comment in February, 1987 4
- Extensive comments received from many sources
- Covernment agencies I
- Utilities
- Academin l
- Public interest groups
- Nuclear induntry
- Private citizens
- Peer review comments obtained
- Uncertainty analysis review, II. Kouts Chairman, NUREG/CR-5000 (December, 1987)
- Overall review. W. Kastenberg, Cinairman, NUREG/CR-5113 (May, 1988) t l
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NUREG-1150 OBJECTIVES
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- TO PROVIDE A CURRENT ASSESShmNT OF TIIE SEVERE ACCIDENT RISKS OF FIVE NUCLEAR POWER PLANTS WLIICII o PROVIDE A SNAPSIIOT OF RISKS REFLECTING PLANT DESIGN AND OPERATIONAL CITAACTERISTICS, FAILURE DATA, AND SEVERE ACCIDENT I
PHENOMENOLOGICAL INFORMATION AVAILABLE IN MARCII. 1000, I
o UPDATES THE ESTIEATES OF TIIE REACTOR SAFETY STUDY, o INCLUDES QUANTITATIVE ESTIMATES OF RISK UNCERTAIN'IT, o IDENTIFES PIANT-SPECIFIC RISK VULNERADILITIES.
- SUMMARIZE TIIE Pr.RSPECTIVES GAINED VITH RESPECT TO o ISSUES SIGNIFICANT TO SEVERE ACCIDENT FREQUENCES, CONSEQUENCES. AND RISKS, o RISK SIGNIFICANT UNCERTAINTIES WHICH MAY h RIT FURTHER
- RESEARCH, o COMPARISONS WITH THE SAFETY GOALS, o POTENTIAL BENEFITS OF A SEVERE ACCIDENT MANAGEMENT PROGRAM, o POTENTIAL DENEFITS OF OTIIER PLANT MODIFICATIONS IN l
RISK REDUCTION.
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- TO PROVIDE METIIODS USEFUL FOR TIIE PRIORITIZATION OF POTENTIAL SAFETY ISSUES AND RELATED RESEARCD.
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NUREG-1150 IMPROVEMENTS ACCIDENT FREQUENCY ANALYSIS
- INCORPORATING INDUSTRY COMMENTS
- REFLECTING CURRENT. DESIGN AND OPERATIONAL PRACTICES
- IMPROVED REACTOR COOLANT PUMP SEAL LOCA MODEL
- EX.etINING BOUNDARY COND.'!TIONS AND ASSUMPTIONS
- STEAM GENERATOR TUBE RUPTURE
- INSTRUMENT AIR
- INCORPORATING SENSITIVITY STUDIES INTO UNCERTAINTY ANALYSIS
- EXPERT PANELS FORMED FOR CERTAIN ISSUES
- SEAL LOCA
- PUMP PERFORMANCE BEYOND DESIGN CONDITIONS
- RECOVERY ACTIONS OUTSIDE WRITTEN PROCEDURES
- CCW PIPING FAILURE RATE
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EXPERT JUDGMENT
~ VASTLY IMPROVED PROCESS USING DECISION - THEORETIC TECHNIQUES.
PROCESS INVOLVES:
NORMATIVE TRAINING
- 1ST SESSION DEFINING ISSUES 6-8 WEEKS FOR EXPERTS TO REVIEW MATERIAL. SURVCY LITERATURE.
PERFORM AN ALYSES 214D SESSION - EXPERTS EXihtta VIEWS: PRIVATE ELICITATION EXPERTS CONTROL PROCESS:
ISSUES ARE OECOMPOSED Bir EACil EXPERT INDIVIDUALLY NEW ISSUES CAN DE ADDED OR THOSE PROPOSED CAN DE DISCARDED CAN RETUSE TO DE ELICITED AND CALL FOR ANOTHER PANEL. E.G.,
SOURCE TERM ANALYSES STCP RUNS FOR ALL IMPORTANT SEQUENCES "VALIDATION ** OF XSOR CODES IN PROGRESS BY "8ENCHMARKING" l
AGAINST NEW STCP rut 4S LINE BY LillE CODING REVIEW i
DROP "CENTRAL" SOURCE TERM IMPROVED DOCUMENTATION i
CONSEQUEiNCE ANALYSIS COMPLETELY REANALYZED RE-EVALUATING ASSUMPTIONS REGARDING EVACUATION RELOCATION I1ADI ATION PROTECllON MEASURES l
ANALYSES OF UNCERTAINTY FROM CONSEQUENCE MODEL!NG UNDERWAY MACCS 1.5 BEING BENCHMARKED AGAINST CSNI STANDARD PROBLEMS
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EXTERNAL EVENT ANALYSIS PROGESSING WELL STUDY LIMITED TO SURRY AND PEACH BOTTOM SEISMIC AND FIRE CONSIDERED FOR CACil SCREENING ANALYGIS TORilADO HURRICANE l
FLOCDING AIRPLANE CRASH TRANSPORTATIO N ANALYTICAL PROCEDURES SIMILAR TO THAT USED FOR RECENT STATION BLACKOUT STUDIES STRUCTURAL FAILURES ADDED h
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Princical MilestoneA for Comoletion of NUREG-1150 Proiggi Date Milestone l
July 8 Complete accident frequency analyses October 1 Complete risk analyses (NUREG/CR-4551)
October 7 Complete accident frequency analysis documentatian (NUREG/CR-4550, Rev. 1)
December 30 Complete risk analysis documentation (NUREG/CR-4551)
(except Vo)ume 2 documenting details of expert elicitation)
December 30 Complete NUREG-1150, Summary Report and Appendices L
January, 1989 Distribution of
- NUREG/CR-4550, Rev. 1 i
- NUREG/CR-4551 (except Volume 2)
February, 1989 Complete NUREG/CR-4551, Volume 2 March, 1989 Distribution of NUREG/CR-4551, Volume 2
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INDIVIDUAL PLAT EXAMINATION FOR EXTERIAL EVOITS ACRS SUBCO MITTEE ON SEVERE ACCIDENTS LAWRENCE C, SHAO, DIRECTOR
. DIVISION OF ENGifEERING AND SYSTDiS TEOf0 LOGY 0*I& OF NUCLEAR REACTOR REGULATION JULY 13, 1988 1
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i ISSUES FOR EXTERML EVBITS i
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MANY POSSIBLE SOURCES OF HAZARDS i
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DES Gil BASES ARE ltM10WN (MAY NOT BE CONSISTDfT) i l
l PRA'S If01CATE HIGH RISKS DUE TO ERTAIN EXTERML EVDITS l
POPE E?fHASIS 01 IllTEMlAL EVBilo !!1 THE PAST l
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EED APPROACES FOR EVALUAT!flG VARIOUS EXTERNAL EVOITS BEYOf0 DESIGl BASES
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I PAST ENHASIS ON INTER 4AL EVENTS i
NO CONCENTRA1D EFFORTS ON EXTMAL EVENTS i
NRC FORED EXTERIAL EVENTS STEERING GROUP
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