ML20214N870

Submits Info Re Main Accomplishments of Research Program & Way Info Should Be Used in Implementation of Integration of Source Term & Severe Accident Programs,Per Request in 861119 Staff Requirements Memo Re Draft NUREG-1150 Publication

ML20214N870
Person / Time
Issue date:	02/17/1987
From:	Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
To:	Asselstine, Roberts, Zech NRC COMMISSION (OCM)
References
REF-10CFR9.7, RTR-NUREG-1150 NUDOCS 8706030119
Download: ML20214N870 (10)

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%,*****/ February 17, 1987 i

MEMORANDUM FOR: Chairman Zech Comissioner Roberts Comissioner Asselstine Commissioner Bernthal Comissioner Carr FROM: Victor Stello, Jr.

Executive Director for Operations

SUBJECT:

INTEGRATION OF SOURCE TERM AND SEVERE ACCIDENT PROGRAMS

Reference:

Staff Requirements Memorandum, " Briefing in Advance of Publication of Draft NUREG-1150 (Source Term) 2:00 p.m.,

Wednesday, November 19, 1986, Comissioners' Conference l Room, D.C. office (open to public attendance) l j Introduction As described in the reference (attached), Chairman Zech requested the 1 staff to submit a paper, outlining how policy matters related to implementing the safety goal policy, severe accident policy, source term efforts, and other important issues relating to severe accident!, such as lessons learned from Chernobyl, are being integrated into a e .istent p.rogram.

For the past five years NRC has undertaken an intensive program to understand and cuantify severc accident phenomenology and source terms.

The first phase of the program consists mainly of research activities.

The purpose of these activities is to develop a better understanding of physical phenomena associated with severe accidents, to develop analytical tools to analyze postulated severe accident sequences, and to assess selected reference plants. The second phase of the program is the implementation phase. Its objective is to evaluate the sufficiency of existing plants relative to the prevention and mitigation of severe accidents, the development of guidance for new plants, and modification of regulations, if appropriate, based on the findings of the research phase.

The following sections present the main accomplishments of the research program, together with the way this information is to be used in the implementation program. Other Commission initiatives, such as the Safety Goal Policy and lessons learned from Chernobyl, also play a role in the severe accident program. These are also discussed t'ricw. )

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1 8706030119 870217 '

PDR 10CFR PT9.7 PDR r ~ . , ,_,, - - . - . .

p j-Severe Accident Research Program l ^*

Technical Issues One of the main objectives of the Severe Accident Research Program (SARP) has been the identification and resolution of technical issues arising from the complex phenomena encountered during postulated LWR meltdown events. The important phenomena of such events encompass the use of the sciences of physics, chemistry, thermodynamics, and mathematical modeling l to an extent rarely encountered in practical applications of scientific '

i principles. For example, models are needed to account for temperature ranges from 300'C to over 2800'C; pressure ranges from 10 psia to 2200 psia; simultaneously-present phases of liquids, solids, and gases; hundreds of chemical species and compounds; and complex geometric and structural environments. The methodology used to resolve such a prodig-

ious problem usually requires it to be divided into several phenomeno-

! logical areas over the time period of the accident sequence. As a result,  ;

certain phenomena can be identified which have large uncertainties or  :

I alternate modeling descriptions (due to the lack of physical and chemical l i data) associated with them. When this occurs, a " technical issue" or i

" technical area of uncertainty" is identified.

It is the resolution of and the cuantification of the uncertainties associ-4 ated with these issues which will provide the principal backup for the 1 implementation of the Comission's Severe Accident Policy Statement (SAPS) over the next few years. Research staff members have been working and will continue to work closely with those involved in inplementing the SAPS, to provide the needed data and analytical techniques.

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The eight major technical areas of uncertainty identified by one program for source term avaluation are as follows

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Patural circulation in the reactor coolant system t

Core melt progression F: hydrogen generation IZircaloy 0xidationi )

Steam explosions resulting in containment failure Failure of containment by high pressure melt ejection (Direct Heating) l l Core concrete interactions, fission product behavior, and heat  !

transfer Hydrogen ignition and burning in containment

! Fission product behavior and chemical form IIedine) in the Reactor Coolant System Revaporization of previously deposited fission products i

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' Major research accomplishments which have and will continue to reduce l

' uncertainties in the above areas and aid in the implementation of the t

Severe Accident Policy Statement include:

• The Source Term Reassessment program (NUREG-0956) which provides the current basic methodology for analyzing severe accidents.

The RES experimental programs in the PBF, NRU, and ACRR which have produced important code validation data for both current models l

and new advanced models of core melt progression.

The experimental programs on fission product release, deposition, and transport which have provided a validation data base for NRC's basic models of release, revaporization, iodine chemical form, and aerosol behavior.

The experimental programs on containment loading which have and will continue to be used to better characterize and reduce

! uncertainties in direct containment heating,~ core / concrete interactions, hydrogen ignition and burning, and steam explosions.

Finally the program has produced a coupled set of detailed, mechanistic phenomenological models which are essential to

assessing these uncertainties in a scientifically sound manner for decision making.

j. NUREG-1150 plant Analyses a The research program is also developing probabilistic risk ar*1yses for six reference plants (Surry, Sequoyah, Zion, Peach Bottom, G: nd Gulf, and LaSalle). A draft report, NUREG-1150, covering internal ever. for the first five of these will be available in February and for LaSu le in the i spring of the 1987. The final report, including selected external event i analyses for some plants, will be available by early 1988.

NUREG-1150 will include identification of significant contributors to core melt frequences, containrent failure probabilities and uncertainties. By providing information on the relative significance of various equipment j failures, operator perfomance, severe accident phenomena, source terms, containment performance and health consequences for a broader sample of plants than previously available, NUREG-1150 supports implementation of the Severe Accident Policy Statement and the Safety Goal Policy. An early 4

application will be to support a decision on how to proceed with develop-  ;

ment of requirements for FARK I RWRs. NUREG-1150 will also provide information to assist in revision to regulations such as for emergency 1 preparedness and siting, and for establishing pricrities for continuing i research to further reduce uncertainties in severe accident phenomena, i

i Vhile the information from Draft NUPEG-1150 must he used with care it will i nonetheless provide useful insights for the aforenentiened applications, i

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. 4 1mplementation Program for the Severe Accident Policy and for the Reculatory  :

Use of New Source Ter1n Information Program Elements i An implementation plan was initially developed in early 1986 and

documented in SECY-86-76. The program now consists of four major i elements, namely 1

examination of existing plants for severe accident vulnerabilities development of guidance for new plants with respect to severe accidents and the use of PRA methods, l'

• introduction cf realistic source tems into licensing (SECY-M-??O

• treatment of external events in severe accident considerations l (SECY-86-162)

Sources of Information The severe accident policy implementation program relies on information i currently available on severe accidents. This includes present under-standing of severe accident phenomena, such as core melt progression, core concrete interactions, hydrogen and fission product generation, contain-j ment loading and containment performance. Much of this information has i been and continues to be generated as part of P!RC's research program.

Additional data and understanding comes from industry and for jn research i programs.

I Another important input to the implementation program is the t ,ssment of l reference plants representing common plant types. Four reference plants have been selected for analysis by both the NRC research program and ,

industryIIDCOP). The results of the NRC analyses are documented in  ;

NUREG-1150. These analyses provide information on the likelihood of se-

vere accidents as well as on the performance of plant specific protective -

j features; e.g., containments. Since current in'orration regarding severe l accident phehomena is still incomplete in certain areas, uncertainties j play an important role in the plant assessments. The PPC assessment of uncertainties in NUREG-1150 and uncertainty analyses available from indus-try sponsored PRAs are major sources of information.

I NRC's research program is also addressing the questions of what are the main contributors to public risk and what can be done to reduce risk. The risk reduction studies and cost benefit analysis presented in MIRFG-1150 l will te used as background information in the implerentation program.

1 The reference plant analyses, both the IDCOR and TPC analysts, were rather

detailed and expensive. One of the goals of the irplementation program is to take advantage of the knowledge available fror the reference plant

anaiyses, tnus making the individual plant examinations simpler and

cheaper. As part of the program, a relatively simple rethodology has been

5 t- developed by the industry (IDCOR) for future use by utilities. This j, methodology (IPEM)iscurrentlyunderstaffreview.

- The NRC staff has been reviewing PRAs for a number of years and has par-l ticipated in the preparation of PRA guide documents. Insights gained from i past PRAs have been evaluated by both NRC and industry and were discussed

at PRA workshops and meetings. These insights, together with the regula-l tory experience gained from the resolution of generic safety issues, pro-j vide further input to the implementation program.

I Figure 1, presents the schematics of information flow to the implementa-j tion program and the program main products.

) Execution of the Program 1

Individual plant examinations for existing plants will be conducted by.

i Licensees. NRC, through a generic letter, will request the examinations j and will provide help and guidance for the examination including the staff  :

approval of the IPEM. NRC positions derived from the resolution of ge-j neric issues (ATWS rule, hydrogen rule, station blackout) will be part of 1 the guidance. Future plants will be required to perform a PRA. NRC will issue, through the normal public process, guidance on the required scope j of the PRA and on the role the PPA will play in the licensing process for i future plants.

i l Source term related changes in rules, regulatory guides and standard re-view plans will be processed in sequence based upon the priority of the issue and the availability of information. Details are provided in SECY-86-76.

! A proposed corollary effort relating to specific safety enhancements to i improve severe accident mitigation capabilities of BWR containments has 1

been discussed with utility owners, the ACRS, and with the Commission, 1

with particular reference to the Mark I design. The basic question ad- l 1 dressed is whether Mark I BHR containment designs are more vulnerable to i severe accidents than other plants, and if so, whether this warrants j special initiatives to eliminate or otherwise mitigate the vulnerabil-j 'ities. In this regard, there is a question of how to balance resource expenditures to reduce the likelihood of severe fuel damage against re-sources to more effectively mitigate the consequences of severe fuel j damage. The consideration of these issues for one class of plants at this

, time while proceeding with other plant evaluations is consistent with the l Severe Accident Policy Statement which explicitly allowed for such action, i THis matter is still under censideration and a separate Commission paper j is in preparation.

j External events are currently not proposed to t e included in the plant

assessments although we would not discourage any licensee from including

{ this in their assessment at this time. The IDCOR rethodology (IPEM) also l does not propose to cover external events. Developtert of an equivalent ,

j iwthodology is underway as part of the Nr.C research programs, it is the l 1 staff's intent to handle external events in a similar nanner as internal

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6 events, but on a separate schedule. Initiation of the external event examinations, if needed, is expected in the first half of 1988.

Role of the Safety Goal Policy Statement The Commission's safety goal policy provides cuantitative guidance for the lic mortality risks as well as the related overall frequency (i.e., (10 staff in terms of the acceptable level of pg/RY the environment that would threaten these risk levels. We intend to im-plement this guidance in the process of the individual plant examinations carried out pursuant to the severe accident policy. Should specific plant vulnerabilities or potential risk outliers be identified, each will be examined with the Commission's safety goal policy in mind. Further, the licensee's judgment, the staff's judgment, the consideration of defense-in-depth and the Comission's Backfit Rule will all be factors that are brought to bear in decisions whether plant improvements should be imple-mented. As noted in the ilanuary 2,1987 memorandum to the Comission concerning the status of safety goal implementation, the general perform-ance guideline for large releases is expected to be a useful surrogate for j the staff to use in implementing the safety goal policy across a number of regulatory issues and program areas including the severe accident policy

, implementation for existing and future plants. Although further study on this general performance guideline is currently ongoing, it appears that this guidance permits some degree of tradeoffs to be made between accident prevention and mitigation while maintaining the traditional defense-in-depth approach. It is also clear that neither the safety goal policy nor the general performance guideline is intended to eliminate existing con-tainment requirements but it does allow sta'f to give an emphasis to i containment performance over a spectrum of severe core damage accidents as

'is currently planned.

Chernoby1 Experience Despite major differences between the design of the Chernoby1 plant and ,

U.S. pover plants, there are lessons to be learned from the Chernobyl )

accident. Severe accident issues which relate to the Chernobyl eccident <

are presently being evaluated. The NRC finding on these issues will be reported in the Chernobyl Implications Assessrent Report. The proposed j

, NRC guidance to licensees will be moWied or expanded if needed, based on i the final Chernobyl implications.

Scheduling Considerations The overall goal of the severe accident program is to assure safe opera-tion of existing plants, protect public safety and brinn sttbility to licensing with respect to severe accident considerations. The program intends to accomplish this to the extent that available infernation and hRC and licensee resources permit. It has been long recognited that parallel e' forts are needed. For example, technical isroes are being rasnived, reference plants are being aralyzed, and guidance 'nr the examination of existing plants is being prepared, concurrently. A .

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Figure 1. Implementation. Program Schematics l

j Reference Plant Analyses IDCORbNRC

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I Understanding of Phenomena Genevic Letter i to Licensees

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t Methodology for l

Plant Examination IDCOR 1

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Implerrientation _ Guidance for Program Future Plants Containment _

r J

Research h Analysis PRA Studies and Guides Source Term

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Related Changes l

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a j Source Term i Research Regulatory Emperienes ,

j and Generic Issues i -

7 chronological listing of recent major accomplishments and projected program goals follows.

1985 ,

Research programs provided a general understanding of severe accident phenomena.

Outstanding technical issues were identified. Programs were developed for the resolution of these issues.

Computer codes were developed for plant analysis.

Reference plant analyses started.

Methodology development for uncertainty assessment started.

The source term report (NUREG-0956) was issued for pubite comment.

The American Physical Society study was completed.

1986 Testing of steel containments was completed.

Source term report (NUREG-0956) was issued in final form.

Uncertainty r,anges of input parameters were cuantified.

. Preliminary inalyses of the reference plants were complet-'

Development of guidelines and criteria for IPE findividual plant examinations) started.

Development of guidance for new plant applications started.

l Work on source term related changes in regulations and regulatory practice started.

1987 Test programs on steam explosions will be completed.

Six reference plant analyses will be completed and documented Ut! PEG-1150 will be issued for comment Generic letter will be issued to initiate IPEs Treatment of BWR Mark I containments will be cecided

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Guidelines for new plant applications will be issued for public coment.

The short term source term related changes will be completed.

1988 Test programs on inteority of concrete containments, hydrogen ignition and burning and fission product transport will be completed.

Detailed uncertainty studks of selected issues will be completed.

NUREG-1150 will be ' issued in final form.

CE and BW reference p, tant analyses will be completed.

l Development of methodology for external event examination will be completed.

Anklyses of two reference plants for ext'ernal initiators will be completed.

Gaidance for examining plants for external events will be issued.

Some of the IPEs will be completed.

Rules, if needed, and regulatory guides for new plant applications will be issued.

Intermediate term source term changes will be completed.

1989 Most severe accident related experbental programs will be completed.

Severe accident code development programs will be completed.

s Issues arising frem plant n aminationr. will be analyzed.

Most IPEs will be completed.

• l Some external event IPEs will be completed, j Long term source term changes will be completed.

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8 The specific actions and responsibilities assigned to the Reactor and Plant System and the Reactor Accident Analysis Divisions within RES, and the necessary coordination with NRR will be described in a memorandumofunderstandingbetweenthetwooffices(RESandNRR)atthe effective date of the reorganization.

(r. -:,: -

Victor Stello, Jr.

Executive Director for Operations ,

cc:

SECY OGC DIST: Subj, Circ,Chron,Silberberg,Burdick, Morris, Rosztoczy,Ross,Beckjord,Sheron,Speis,Marino, Stello, Roe, Rehm, Sniezek, Denton, Taylor, Murray TEXT R/F

• See previous concurrence sheet

• • Memo changed in DEDROGR.

Dh5.AEB D S:P/B DRSS:Act.Dir. RES:DD SI ERBERG BUR CK MORRIS ROSS 87 1/ 7 1/30/87

• 2/11/87*

RES: EDQ NRR NRR NRR BECKJ0RD S' SHERON SPEIS DENTON

. ,1// 9/87 @fLg/870 1/30/87* 2/5 /87

• 2/5/87*

Telephone Telephone Concurred Concurred

IN RESPONSE, PLEASE

, .j c "4 UMTED STATES P ,,

NUCLEAR REGULATORY COMMISSION

.; y . ,i . WASHINGTON, D.C. 20555 ACTION - Beckjord  :

S e December 1, 1986 o,j Cys: Stello CFFICE OF THE Roe SECRETARY Rehm Denton Taylor Murray MEMORANDUM FOR: Victor Stello, Jr.

Executive Director for C rations FROM:

SamuelJ.Chilk,SecreIi a }

SUBJECT:

STAFF REQUIREMENTS - BR 1 ING IN ADVANCE OF PUBLICATION OF DRAFT NU  ;-1150 (SOURCE TERM),  ;

2:00 P.M., WEDNESDAY, NOVEMBER 19, 1986, l COMMISSIONERS' CONFERENCE ROOM, D.C. OFFICE (OPEN TO PUBLIC ATTENDANCE)

The Commission was briefed by the staff on the status of its source tern effort as it relates to publication of draft NUREG-ll50.

The Commission requested the staff to address durin, .:s quarterly source term briefing, scheduled for December 17, 1986, the following items:

Resources needed for program completion.

Esalistic schedule for program completion.

If additional funding would provide a quicker resolution to the direct containment heating and similar outstanding technical issues.

Chairman Zech requested the staff to submit a paper, prior to the January 15, 1987, meeting, outlining how policy matters related to implementing the safety goal policy, severe accident policy, source term efforts, and other important issues, such as the lessons learned from Chernobyl, are being integrated into a consistent overall program.

JEDOk (RES) (SECY Suspense: 1/9/B7) l 1

The staff stated that its upcoming Commission paper would I address Commissioner Asselstine's question as to whether the research program canceled due to funding constraints would have reduced any of the uncertainties in the results of MUREG-ll50.

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e' Commissioner Carr referenced page 11-9 of draft NUREG-1150 which stated that the staff would develop and propose guidelines for Commission approval which will be used as a basis for determin-ing whether a level of safety ascribed to a plant is consistent with the safety goal policy. He requested the staff to provide its schedule for submitting that paper.

4809) (RES) (SECY Suspense: 12/12/86)

The staff recommended to reserve time in mid-January 1987, to brief the Commission on the final version of draft NUREG-1150, just prior to its publication.

(Subsequently, SECY tentatively scheduled the briefing for January 15, 1987.)

cc: Chairman Zech Commissioner Roberts Commissioner Asselstine Commissioner Bernthal Commissioner Carr Commission Staff Offices PDR - Advance DCS - 016 Phillipe Q

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