ML20205C661

Summary of ACRS Subcommittee on Containment Requirements 861209 Meeting in Washington,Dc Re Proposed Generic Ltr on BWR Mark I Containment Requirements,Including Discussion of BWR Emergency Procedure Guidelines.Agenda & Viewgraphs Encl

ML20205C661
Person / Time
Issue date:	12/23/1986
From:	Advisory Committee on Reactor Safeguards
To:	Advisory Committee on Reactor Safeguards
References
ACRS-2477, NUDOCS 8703300232
Download: ML20205C661 (30)

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b EiN Q k DATE ISSUED: 12/23/86 343/n ACRS SUBCOMMITTEE MEETING

SUMMARY

/ MINUTES FOR CONTAINMENT REQUIREMENTS DECEMBER 9, 1986 WASHINGTON, DC Purpose The ACRS Subcommittee on Containment Requirements met on December 9, 1986 in Washington, DC. The purpose of this meeting was to discuss the Staff's (NRR) proposed generic letter on BWR Mark I containment require-ments, including a discussion of BWR Emergency Procedure Guidelines (EPGs) which include guidance for containment venting. The Subcommittee heard presentations from members of NRC/NRR and BWR Owners' Group (BWROG). Copies of the agenda and selected slides from the presen-tations are attached. The meeting began at 1:00 p.m. and adjourned at 5:30 p.m., and was held entirely in open session. The principal attend-ees were as follows:

Attendees ACRS NRC/NRR C. Mark, Chairman R. Bernero J. Ebersole, Member W. Hodges W. Kerr, Member G. Thomas C. Michelson, Member C. Siess, Member BWROG C. Wylie, Member I. Catton, Consultant Terry Pickens (NSP)

D. Houston, Staff Discussion In his opening statement, C. Mark drew attention to the communications by Commissioner Asselstine and D. Okrent, in which they individually expressed their strong support to the proposed BWR Mark I improvements.

R. Bernero (NRR) discussed the details of the proposed generic letter on improvements for BWR Mark I containments. In support of the proposed required actions, he reviewed the NRC Severe Accident Policy Statement, portions of GDC 16 and 50 and the IDCOR/NRC programs in regard to DESIGNATED ORIGINAL h PDR certified By S _

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b Containment Requirements Minutes December 9, 1986 reference plant studies and Individual Plant Examinations (IPE). He -

discussed the characteristics of BWR Mark Is and indicated that Mark I containments were vulnerable due to their small volume (<lll, 300,000 cu.

ft.) and small drywell floor area. He presented the details of a five element program for the improvement of Mark I containments. These elements and a brief description are as follows:

1. Hydrogen control - no additional requirements, 10 CFR 50.44 and Tech Specs sufficient.

2. _ Containment Sprays - need for a primary supply system and two backup systems (one with independent power) for the drywell sprays.

In addition, the spray flow rates would be reduced by 90% to an approximate value of 800 gpm by modifications to the spray headers.

3. Pressure relief - a procedure shall be developed for venting of the containment when the pressure approaches the range from design pressure to 1.5 times design pressure.

4. Core debris control - assurance that water in the suppression pool in the event of torus failure would be held within the confines of the tcrus room.

5. Procedures and Training - implementation of BWR Emergency Procedure Guidelines, Revision 4 as finally approved by NRC.

R. Bernero also discussed the conditions for these improvements.

Briefly they are: (1) need not meet the quality or standards of safety related equipment, (2) installed during first refueling outage from specified date, and (3) gives relief for those plants with +.ie improvements to omit an IPE for containment performance. He concluded with a brief discussion of a preliminary cost-benefit analysis and a tentative schedule for issuing the generic letter (February 1, 1987 for public comment and May 1987 for final.)

D Containment Requirements Minutes December 9, 1986 I

T. Pickens (NSP-BWR0G) briefly discussed the BWROG/NUMARC program which has been developed and in progress to address the concerns of the NRC for the Mark I containments. Their program will assess the aspects of l the proposed requirements as well as the challenges.to and the capabil- '

ity of the containment structure. He indicated that the studies would be completed in the March-April 1987 time frame.

G. Thomas (NRR)discussedtheBWREmergencyProceduresGuidelines(EPG)

(Revision 4) which are currently under review by the Staff. He gave an overview of the EPGs, discussing the purpose and entry conditions for five guidelines area: (1) RPV control, (2) primary containment control, (3) secondary containment control, (4) radioactivity release control, and(5) contingencies. He discussed the functional requirements for the EPGs and the spectrum of emergencies to be addressed by them, mostly DBAs. He concluded with a review of containment venting considerations for both pressure control and combustible gas co. trol. The Staff has approved EPGs for venting in Revision 2 and 3, this approval about two years ago. The Staff's initial review of Revision 4 is expected to be completed in March 1987 with a final Safety Evaluation Report in July l

1987.

During the meeting, Subcommittee members and consultants expressed concerns and opinions as follows:

l (1) C. Mark asked whether any Mark Is evaluated in the reference plant or IPE studies had received NRC approval. (Bernero answered that t none had.) He expressed a concern that the time frame for imple-mentation of the improvements would be insufficient for analysis, modifications and FSAR charges. He inquired about the use of a filtered vent and expressed dissatisfaction with the cost-benefit analysis.

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• Containment Requirements Minutes December 9, 1986 (2) C. Siess questioned the basis for an acceptable containment failure rate and indicated that this generic letter migh,t establish a defacto containment performance design objective of 0.01 for conditional containment failure probability in the event of a severe accident. He questioned the melt progression and drywell spray sequences and the uncertainties in the calculations. He also indicated that the generic letter should be revised to show that the letter in its title and introduction was concerned with BWR Mark Is only.

(3) J. Ebersole asked if any consideration had been given to the plant improvements that had been made since WASH-1400 in the NRR dis-cussion of conditional containment failure probability (none had).

He indicated it n:ould be better to vent containment to prevent core melt through the use of low pressure water systems than to hold it as a mitigating feature. He also felt the highest priority should be given to spraying water on the core, given a choice between drywell and core spray systems. He expressed concerns about venting containment when the suppression pool temperature is near saturation, thereby disabling systems that operate from the pool.

(4) C. Michelson questioned the reduction in drywell spray flow rates and the sequence for spray initiation and expressed concerns about the loss of vapor suppression processes. He asked how the concerns of Generic Issue 61 had been considered, a postulated rupture of an SRV pipe inside the torus. He felt that the containment design pressure would be reached in minutes after a rupture while the Staff indicated about 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. He questioned the instructions given to the operators if they saw a rapid rise in containment pressure. Also, he questioned if the procedures are written to recover after an operator error. He was concerned about the amount of water added to containment and requested information about the water level instrumentation in the torus and containment.

e Containment Requirements Minutes December 9, 1986 i

(5) W. Kerr questioned the definition of core melt, i.e., onset of severe core damage or core on the floor and asked how one obtained confidence in the containment behavior from the proposed improve-ments.

(6) I. Catton questioned the sequence of spray cooling the debris in the lower cavity, thus forming a crust and agglomerating the corium under the vessel. He asked the Staff to give further consideration to this matter.

• • • • • • • • • • • • • • • • • • • • • • • • • l NOTE: Additional meeting details can be obtained from a transcript ,

, of this meeting available in the NRC Public Document Room,

) 1717 H Street, N.W., Washington, D.C., or can be purchased from ACE-Federal Reporters, 444 North Capitol Street, Wash-ington, DC 20001, (202) 347-3700.

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ACRS Containment Requirements Subccmmittee Meeting December 9, 1986 Washington, DC

- Tentative Presentation Schedule -

BWR Mark I Containment Requirements A. Subcommittee Chairman Remarks C. Mark 1:00 pm B.- NRR BWR mark I Containment R. Bernero 1:10 pm Requirements - Draft Generic NRR Letter

• • • Break *** 2:30-2:40 pm C. BWR Emergency Procedure Guidelines, Revision 4

• Overview

• Containment Venting G. Thomas 3:30 pm NRR D. Subcommittee Remarks C. Mark 4:45 pm

• • • Adjourn *** 5:00 pm ACRS

Contact:

Dean Houston (202) 634-3267

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PROPOSED BWR SEVERE ACCIDENT CONTAINMENT REQUIREMEliTS -

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R. M. BERNER0 l

DECEIGER 9,1986 1

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NRC SEVERE CCIDENT POLICY e AUGUST 8, 1985 e PRESENT REACTORS ARE SAFE EtiOUGH, BUT...

1 e SEARCH FOR OUTLIERS e CONSIDER EALANCE OF PREVENTION AND MITIGATION SPECIAL CONSIDERATION OF CONTAINf!ENT PERFORf"ANCE I

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1 GDC 16:

CRITERION 16 - CONTAINMENT DESIGN, "

--AN ESSENTIALLY LEAK-TIGHT BARRIER AGAINST THE UNCONTROLLED RELEASE OF RADI0 ACTIVITY TO THE ENVIRONMEi4T AND TO ASSURE THAT THE C0i1 Tali 4 MENT DESIGN CONDITIONS IMPORTANT TO SAFETY ARE NOT EXCEEDED FOR AS L0iiG AS POSTULATED ACCIDENT C0iiDITI0iiS REQUIRE."

GDC 50:

CRITERION 50 - CONTAINMENT DESIGN BASIS. --AS REQUIRED BY SECTION 50.44, ENERGY FROM METAL-WATER AND OTHER CHEMICAL REACTIONS THAT MAY RESULT FROM DEGRADATION BUT NOT TOTAL FAILURE OF E"ERGENCY CORE COOLING FUliCTIONING, (2) THE Lli',ITED EXPERIENCE 1liD EIRIf,Ei1TAL DATA AVAILABLE FOR DEFliilNG ACCIDENT PHENOMENA AND CONTAINMENT RESPONSES, AllD (3) THE CONSERVATISM 0F THE CALCUi_ATIONAL MODEL AND INPUT PARAMETERS."

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IDCORINRCPROCESS e TKO PARALLEL PROGRAMS TO STUDY SEVERE ACCIDENTS IN REFERENCE PLANTS NRC SEVERE ACCIDENT PROGRAM IDCOR e COMPARE AND RESOLVE TECHNICAL ISSUES e IDCOR PREPARE AND SUBMIT IPE METHODOLOGY FOR NRC REVIEW e NRC GENERIC LETTER TO DO IPE WITH GUIDELINES & CRITERIA BY APPROVED METHODOLOGY e CONDUCT IPE e IDENTIFY AND EVALUATE OUTLEIRS e ORDER FIXES  ;

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7 KEY RESULTS FOR BWR CONTAINMENTS e REACTOR SAFETY STUDY - PEACH BOTTOM 90% EARLY RELEASE e IDCOR - PEACH BOTT0fi 20% EARLY RELEASE e VERM0i1T YANKEE - 7% EARLY RELEASE e NUREG-1150 I

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s 10 BWR C0iiTAli4 MENT ISSUES - IMRK I .

e SMALL VOLUME MORE RAPID OVERPRESSURE ESPECIALLY VULNERABLE TO HYDR 0 GEN BURN e SIMLL DRYWELL FLOOR LOWER HEAD AREA CLOSE TO DRYkTEl.l. MAI.L POTENTIAL FOR DIRECT DEBRIS ATTACK DIRECT RADIATION AND CONVECTION hTATING e LIMITED PASSIVE CAPABILITY BUT OPTIONS FOR ACTIVE RESPONSE e 5-ELEMENT APPROACH HYDROGEN CONTROL SPRAY IN DRYWELL PRESSURE RELIEF DEBRIS CONTROL

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l PROCEDURES AND TRAINING 1

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• 11 CONTAINMENT IMPROVEMENT STR TEGY o PREVENT HYDROGEN COMBUSTION BY INERTING e REDUCE DRYWELL SPRAY FLOW RATE PERMITS ALTERNATE SUPPLIES TO PRODUCE SPRAY EXTENDS WATER SUPPLIES s PROVIDE RELIABLE BACKUP SUPPLIES FOR DRYWELL SPRAY PROVIDES SHALLOW POOL OF WATER ON DRYWELL FLOOR DIRECT SPRAY COOLING 0F ANY CORE DEBRIS LEAVING LOWER HEAD AREA SPRAY SCRUBBING OF DRYWELL VOLUME DIRECT COOLING OF WALLS e WETWELL PRESSURE RELIEF TO STACK POOL SCRUBBING ELEVATED RELEASE e DEBRIS CONFINEMENT e TRAINED OPERATORS -t

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PROF 0 SED REQUIREF.ENTS

1. HYDROGEN CONTROL PRESENT REGUIREMENTS IMPOSED BY 10 CFR PART 50,44 AND THE TECHNICAL SPECIFICATIONS SHALL BE ADHERED T0, NO ADDITIONAL REQUIREMENTS ARE PROPOSED,

2. CONTAINMENT SPRAY ALL BWRs WITH MARK I CONTAINMENT SHALL PROVIDE AT LEAST TWO BACKUP WATER SUPPLY SYSTEMS FOR THE CONTAINMENT DRYWELL SPRAY, ONE OF WHICH SHALL BE FUNCTIONAL DURING STATION BLACKOUT.

WATER TO THE SPRAY SYSTEtt FROM THESE BACKUP SUPPLIES SHALL BE AVAILABLE BY REMOTE l'ANUAL OPERATION OR BY SIMPLE PROCEDURES FOR CONNECTION AND STARTUP WHICH CAN BE IMPLEMENTED DURING A SEVERE ACCIDENT SCENARIO,

^ IN AEDITION, THE SPRAY N0ZZLES SHALL BE ADJUSTED S0 THAT

, AN EVENLY DISTRIBUTED SPRAY PATTERN WILL BE DEVELOPED IN THE DRYWELL WHETHER WATER IS SUPPLIEB BY THE PRIMARY SOURCE OR EITHER OF THE BACKUP SOURCES. A FLOW RATE ON THE ORDER OF 1/10 0F THE PRESENT FLOW RATE IS CONSIDERED TYPICAL, THE LICENSEE SHALL SELECT THE FLOW BASED ON AN ANALYSIS OF .

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- 15 PROPOSED REQUIREMENTS (CONT'D.)

3. PRESSURE RELIEF THE LICENSEE SHALL SELECT A PRESSURE BETWEEN DESIGN PRESSURE AND 1h TIMES DESIGN PRESSURE AT WHICH TO OPEN AN EXHAUST PATH FROM THE WETWELL VAPOR SPACE TO THE HIGHEST VENT POINT (STACK OR PIPE) AVAILABLE. THIS LINE SHOULD BE CAPABLE OF HANDLING WATER VAPOR FLOW EQUIVALENT TO 1%

DECAY HEAT AT THE VENT PRESSURE SELECTED WITHOUT SIGNIFICANT CHANCE OF RUPTURE BEFORE THE DESIRED RELEASE POINT. THE LINE SHALL BE EQUIPPED WITH ISOLATION VALVES WHICH CAN BE OPENED AND RECLOSED BY REMOTE MANUAL OPERATION OR BY SIMPLE PROCEDURES WHICH CAN BE IMPLEMENTED DURING SEVERE ACCIDENT SCENARIOS INCLUDING STATION BLACK 0UT.

4. CORE DEBRIS CONTROL THE LICENSEE SHALL ENSURE THAT THE WATER IN THE SUPPRESSION POOL IN THE EVENT OF TORUS FAILURE ~ IS HELD WITHIN THE CONFINES OF THE TORUS ROOM AND THE CORNER ROOMS AND CANNOT FLOW OUT TO OTHER PARTS OF THE PLANT.

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5. PROCEDURES AND TRAINING THE LICENSEE SHALL IMPLEMENT EMERGENCY OPERATING PROCEDURES AND OTHER PROCEDURES BASED ON ALL SIGNIFICANT ELEMENTS

' APPROPRIATE TO ITS PLANT OF EMERGENCY PROCEDURE GUIDELINES, REVISION 4.

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CONDITIONS QUALITY AND DESIGN STANDARDS SINCE THESE REGUIREMENTS ARE INTENDED TO BE AN OPTIMIZED USE OF EXISTING EQUIPMENT IT IS EXPECTED THAT ADDED EQUIPMENT, OF ITSELF, NEED NOT MEET THE QUALITY OR DESIGN STANDARDS OF SAFETY RELATED EQUIPMENT, NEVERTHELESS, MODIFICATIONS TO OR NEAR EQUIPMENT OR SYSTEMS WHICH ARE ALREADY SAFETY RELATED SHALL NOT COMPROMISE THE QUALITY OF SUCH EQUIPMENT OR SYSTEMS.

IMPLEMENTATION THE EQUIPhENT CHANGES REQUIRED HEREIN SHALL BE INSTALLED DURING THE FIRST REFUELING OUTAGE WHICH BEGINS NINE (9) MONTHS AFTER THE EFFECTIVE DATE OF THIS LETTER. THE PROCEDURES AND TRAINING REQUIRED SHALL BE If1PLEMENTED ON A SCHEDULE REVIEWED AND APPROVED BY THE NRC. GIVEN THE IliPLEMENTATION OF THE GENERIC IMPROVEMENTS OF MARK I CONTAINMENTS THERE IS N0 NEED FOR AN INDIVIDUAL PLANT EVALUATION (IPE) FOR CONTAINMENT PERFORMANCE. THIS DOES NOT REMOVE THE HEED FOR AN IPE WHICH COVERS THE SYSTEM RELIABILITY OR CORE MELT FREQUENCY PORTION OF THE SEVERE ACCIDENT QUESTION. ,

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o 19 PROP SED ACTI N e DEC, 9 a 12, 1986 ACRS REVIEW e DEC. 19, 1986 CRGR REVIEW e JANUARY 1987 REVIEW 0F ACRS AND CRGR REACTION WITH COMt'ISSION e FEB, 1, 1987, PUBLISH PROPOSED GENERIC LETTER FOR COMMENT e MAY 1987 ISSUE FINAL GENERIC LETTER SIMILAR LETTERS ON MARK II AND MARK III TO FOLLOW 4

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O EMEFiGENCY PROCEDURE GUIDELINES -

(EPGs)

CONTAINMENT VENTING AND PURGING PRESENTATION TO ACRS SUBCOMMITTEE MEETING DECEMBER 9, 1 9116 George Thomas .

Reactor Systems Branch Division of BWR Licensing Office of Nuclear Reactor Regulation h

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EPGs OVERVIEW O RPV Control Guideline .

O Primary Containment Control Guideline e Secondary Containment Control Guideline O Radioactivity Release Control Guideline .

O Contingencies

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4 RPV CONTROL GUIDELINE .

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j PURPOSE .

1 l e Maintain Adequate Core Cooling I o Shut Down the Reactor e Cool Down the RPV to Cold Shutdown Conditions 1

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! ENTRY CONDITIONS J

i i e Low RPV Water Level e High RPV Pressure .

e High Drywell Pressure ,

'e A Condition Which Requires SCRAM ,

i e Reactor Power is Above APRM Downscale Trip or Cannot Be Determined

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PRIMARY CONTAINMENT '

CONTROL. GUIDELINE

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i PURPOSE 8 Maintain Primary Containment Integrity e Protect Equipment in the Prirnary Contaisiment ENTRY CONDITIONS ,

o High Suppression Pool Temperature ,

o High Drywell Temperature

• High Drywell Pressure -

l I e High/ Low Suppression Pool Water Level ,

1 e High Hydrogen Concentration j .

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! SECONDARY CONTAINMENT .

1 CONTROL GUIDELINE -

PURPOSE i e Limit Radioactivity Release From and To the -

Secondary Containment

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• Maintain Secondary Containment integrity

! e Protect Equipment in the Secondary Containment i

i ENTRY CONDITIONS j

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e High Radiation Level -

J f e High Sump or Area Water Level ,

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j RADIOACTIVITY FIELEASE '

CONTROL GUIDELINE PURPOSE .

o Limit Radioactivity Release into Areas Outside the I Primary and Secondary Containments ENTRY CONDITION

! e Offsite Radioactivity Release Rate Above the.Offsite -

Release Rate Which Requires An Alert

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• i CONTINGENCIES

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i o Coordinates the Same Actions Required in Different Guidelines o Simplify the Guidelines o Required for Plant Degraded Conditions l

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CONTAINMENT VENTING o Status i

0 Primary Containment Pressure Control l

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0 Combustible Gas Control l

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STATUS e Rev. 3 Latest Approved Version Vent to Prevent Containment Failure Failure Pressure Poorly Defined I e Recent Work Done by Owner's Group, NRC Staff /

Contractors, IDCOR Show Several Venting Considerations 1 1. Vent Through Suppression Pool for Scrubbing

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2. Assure Operability of Vent isolation Valves

3. Assure Operability of ADS Valves

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4. Assure Operability of Reactor Vent Valves

[ 5. Degradation of Equipment or Personnel Access i Due to Duct Failure .

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6. Combustible Gas Control ,

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• Rev. 4 Will include These Considerations K

< 2rimary Containment Pressure Control and .

dombustible Gas Control Guidelines include Venting and Purging of Containment ..

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PRIMARY CONTAINMENT PRESSURE CONTRdL t .

CONTROL PRIMARY CONTAINMENT PRESSURE BELOW SCRAM SETPOINT USING:

• CNT PRESSURE CONTROL SYS

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• DW PURGE OPERATE SP SPRAYS.

ACC PERMITTING OPERATE DW SPRAYS.

ACC PERMITTING 1

r-EMERGENCY RPV DEPRESSURIZATION IS REQUIRED 1 r IRRESPECTIVE OF OFFSITE RELEASE RATE VENT PRIM ARY CONTAINMENT OPERATE SP SPRAYS.

. IRRESPECTIVE OF ACC 3 r OPERATE OW SPRAYS.

IRRESPECTIVE OF ACC i ACC ADEQUATE CORE COOUNG

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MARK I/11 PROPOSED COMBUSTIBLE GAS CONTROL GUIDELINES SYhlPTOM/ CONDITION ACTION RADIOACTIVITY RELEASE RATE < LCO VENT SUPPRESSION CHAMBER H2 = 0.5% -

VENT DRYWELL (IF SC CAN NOT BE VENTED)

DEFEAT ISOLATION INTERLOCKS IF NECESSARY t

H2 = 0.5?o AND 02 < Sw ~ INITI ATE DRYWELL NITROGEN PURGE 1

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H2 = 0.5% AND O2 > 5% . INITIATE DRYWELL

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H2 = 1% A00 OPERATE RECOMBINERS

T OPERATE DRYWELL H2

, H2 <6% OR O2 <5% MIXING SYSTEM M

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1 MARK 1/11 PROPOSED COMBUSTIBLE GAS CONTROL GUIDELINES '

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SYMPTOM / CONDITION ACTION H2 = 60o AND 02 = 59o -

SECURE RECOMBINERS I

s DEPRESSURIZE RPV ir SECURE HYDROGEN MIXING SYSTEM

' INITIATE SUPPRESSION PCOL SPRAYS (ACC PERMITrlNG)

IRRESPECTIVE OF RADIOACTIVITY H2 = 6?o AND O 2> 59'o RELE ASE R ATE

- VENT SUPPRESSION CHAMBER l' VENT DRYVVELL (IF SC t- CAN NOT BE VENTED)

INITIATE DRYWELL PURGE s INITIATE DRYWELL SPRAYS 13 (ACC PERMITTING) j l

m lRRESPECTIVE OF ACC h .

H2 > 6% AND O2 > 5% T INITIATE SUPPRESSION POOL SPRAYS INITIATE DRYWELL SPRAYS 5

ACC ADEQUATE CORE COOUNG 2OF2 9

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9 REVIEW SCHEDULE FOR EPGs .

(Rev. 4) l e Started Staff Review of Draft - August 1986 o BWR Owner's Formal Submittal - January 1987 0 Request for Additional Information - March e Response from BWR Owner's Group - May 1987 ,

0 Staff SER - July 1987 i

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