ML091940556

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RCS Natural Circulation Review Meeting on 3/17/1986
ML091940556
Person / Time
Issue date: 05/01/1986
From: Han J
Office of Nuclear Regulatory Research
To: Silberberg M
Office of Nuclear Regulatory Research
Han, James T.
References
Download: ML091940556 (13)
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Text

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I MEMORANDUM FOR:

Mel Silberberg, Chief Fuel Systems Research Branch Division of Accident Evaluation FROM:

James T. Han Fuel System Research Branch Division of Accident Evaluation MAY 1 1986

SUBJECT:

A

SUMMARY

OF MARCH 17,' 1986 MEETING ON RCS NATURAL CIRCULATION STUDIES This ~emo sulTITiarizes the subject meeting held on March 17, 1986 in Bethesda, Maryland.

Objectives of the meeting were to: (1) introduce to NRR staff the RES-sponsored studies on RCS Natural Circulation under TMLB' (Station blackout with no auxiliary feedwater) accident conditions, and (2) seek comments and suggestions from NRR and RES staff on those studies.

RCS Natural Circulation is a NUREG-1150 issue currently under study. This issue has direct impact on other NUREG-1150 issues including direct containment heating, hydrogen generation, melt progression and fission product revaporization.

In addition, RCS Natural Circulation will also address the concern on steam generator (SG) tube rupture which may lead to fission product bypass of the containment.

The meeting was started with my presentation on the overview of RCS Natural Circulation.

I also discussed briefly our plans to resolve this issue by using the detailed mechanistic codes including MELPROG/TRAC, SCDAP/RELAP5, and COMMIX.

Preliminary TMLB' calculations using those codes were presented by NRC contractors from LANL, SNL, INEL, and ANL.

The meeting went well with active audience participation. A number of questions and interesting comments were raised. There were about 30 people attending the meeting with one-third of them from NRR and the rest from RES and national laboratories. Enclosed are a meeting agenda, the overview of RCS Natural Circulation, a list of attendees, and two commenting letters from the attendees. A set of meeting handouts is available in my office to anyone interested.

The following is a summary of those comments and concerns which may affect the scope and the course of the RES-sponsored studies on RCS Natural Circulation.

1.

It is very difficult to realistically model the natural circulation flow in the SG tubes because we do not know how many tubes will have flow while the rest of the tubes have no flow.

SG tube flow is a transient process - some tubes may have upward flow for a while and then flow direction may be reverse or become stagnant.

This comment addresses the use of the COMMIX code in modeling the flow in the SG tubes.

As a result, we may have to do some parametric study by varying the number of tubes with stagnant flow and making assumptions on flow distribution in the SG.

I Mel Silberberg, Chief 2

MAY 1 1986 2*.

Flow resistance of the cross flow (normal to the axial flow) is important for calculating in-vessel natural circulation. Correla-tions used in the COMMIX or MELPROG/TRAC code need to be examined for applicability under the natural circulation conditions.

I am contacting Westinghouse through NRR to seek any data they may have in this area.

3.

Non-syrrmetric effects among the RCS loop flows need to be considered. This corrment is valid especially during the cyclic opening and closing periods of the PORV or SRV of the pressurizer.

However, three-dimensional modeling in the MELPROG/TRAC code may be needed to address this non-symmetric multi-loop effects. Currently the code is two-dimensional (with axial and radial dimensions) in the vessel and we do not have *.irrmediate plans to make it three-dimensional by adding azimuthal dimension.

Resolution of this concern needs further evaluation.

4.

s';mple experiments have been suggested to assess the above concerns, although we did not have time to discuss what experiments are needed.

However, it is also recognized that before we plan any experiments we should examine closely the existing experiments sponsored by EPRI in which the RCS of a PWR is simulated by a 1/7-scale semicircular vessel with two loops attached using either water or sulfur hexafluoride as coolant.

I have not received the Westinghouse report on the first-phase experiments from EPRI, and I will certainly distribute it to interested staff members for corrments.

5.

Decay heat redistribution due to fission product release and deposition should be modeled.

For example, fission product deposition in the upper plenum region tends to increase the upper plenum surface temperature.

As a result, natural circulation.flow in the vessel will be altered.

We have the plan to add models to both the SCDAP/RELAPS and MELPROG/TRAC codes to address this concern.

6.

Chemical reactions between the upper plenum steel and steam will produce additional hydrogen and also make the upper plenum hotter.

Therefore, the process should be modeled.

We will add models to our codes to include this process.

7.

RCS Natural Circulation is a very difficult problem, in which thermal-hydraulics is coupled with core melt progression, hydrogen generation due to metal-steam reaction, and fission product release and deposition.

As a result, modeling uncertainties are inherently large.

We should expect to relax accuracy requirements for the severe accident analysis codes such as MELPROG/TRAC and SCDAP/RELAPS as compared with thermal-hydraulic codes such as TRAC and RELAPS for design-basis accident analysis.

Mel Silberberg. Chief 3

MAY 1 1986 We are planning to incorporate the above comments to the extent limited by the funding and time constraints." As part of the code development plan. -models are being added to MELPROG/TRAC to account for fission product decay heating on the upper plenum structures (comment no. 5);

these improvements will be included in the next MELPROG/TRAC calculation to be completed in six months.

New results will be reviewed in another meeting in the fall. and we will find out how much effect these improvements have on the hot leg nozzle temperature, which is predicted in the current preliminary MELPROG/TRAC calculation to be around l000°C before the vessel bottom head fails for the Surry Plant under TMLB' conditions.

Finally, I would like to thank all attendees - especially W. Lyon of NRR and N. Zuber of RES - for their conJ11ents and participation.

Enclosures:

As stated DIST:

Subj Circ Chron Branch:RDG Han:RDG:CY Conti:CY Morris:CY Ross:CY Minogue~CY Denton:CY Speis:CY Rosztoczy:CY E lta nil a : CY Read:CY

/5/

James T. Han Fuel System Research Branch Division of Accident Evaluation Curtis:CY Shotkin:CY Zuber:CY Lyon:CY Ernst:CY.

Mitchell :CY Chan:CY Marino:CY Wright:CY Cunningham:CY Leung:CY Allen:CY Palla:CY FSRB ;>tf HAN/dp'v 4/3° /86 FSRBJk)

SILBERBERG 4/'3<>/86

(

MAR 12 1986 Distribution:

Subj Circ Chron h r/f MEMORANDUM FOR:

Distribution FROM:

James T. Han n

r/f MSilberberg RMinogue

SUBJECT:

Fuel Systems Research Branch Division of Accident Evaluation, RES INVITATION TO ATTEND A MEETING ON THE STATUS OF TMLB' STUDIES MONDAY, MARCH 17, 1986 ROOM P-118, PHILLIPS BUILDING 7920 NORFOLK AVENUE, BETHESDA, MARYLAND You are cordially invited to attend a nne-day meeting on the status of PWR TMLB' studies using the detailed mechanistic codes.

Results are preliminary.

Your participation and comments would be appreciated.

Time 8:30 a.m.

9:00 a.m.

9:30 a.m.

Agenda Overview MELPROG Code Introduction 2-0 MELPROG Calculation for TMLB' in the SURRY Plant Speaker J. Han, NRC

,1. Kelly, SNL R. Henninger, LANL 10:30 a.m.

BREAK 10:45 a.m.

11:30 a.m.

12:00 noon 1:10 p.m.

3 : o o P. ""-

~

p. m *

.3:~0 4: 00 p.m.

MELPROG Insight of NUREG-1150 Issues Discussion LUNCH COMMIX Code Applications Sc.PAP/RE.LAPS-cc..l,~l~t~

Discussion Adjourn James T. Han J. Kelly, SNL V. Shah, ANL P. Sa.yless, uJEL Fuel Systems Research Branch Division of Accident Evaluation

~

Office of Nuclear Regulatory Research DAE :FSRB.I DAfytt Han :md !rt Silberberg 3/11/86 3/tl/86

I RCS t~TURAL CIRCUlATIO"J DURING :U:,LB' ACCIIBITS IN A PrlR -.AN CWERvIEW JMS T. HAIL NRC-RES W\\RCH 17) 1986 BETlfSD,l\\i rv1ARYLAND

I Ii O]JWCTIW e TftB' ACCIIINTS:

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I I

l A Summary of NRC-Sponsored Detailed Mechanistic Code Calculations and S_tructural Integrity Studies to ~ddress "RCS Natural Ci rcul ati on*

Coda Usad TRAC-PFl Purpose Calculating upper plenum natural circulation u*sing MARCH-supplied boundary condition* at cor* exit.

Results were provided to BMI-2104 team at BCL.

COBRA-NC Calculating in-vessel natural circulation assuming intact cor* geometry and using MARCH-supplied boundary conditions.

Results were compared with MELPROG/TRAC calculations prior to core degradation.

TRAC-PF1 Calculating in-vessel natural circulation assuming intact core geometry.

Results wer* compared with MELPROG/TRAC calculations prior to core degradation.

HELPROG/TRAC Calculating in-vessel natural circulation up to vessel failura.

No fission product release and retention, hydrogen generation calculatad.

HELPROG/TRAC Sama calculation as above but including fission product release and retention.

Calculation will proceed to soma point aftar vessel failura.

COMMIX Scoping calculations to investigate multi-dimensional natural circulation flow in th* vessel and in th* hot lag piping.

Results will be used to provide guidance to both MELPROG/TRAC and SCDAP/RELAPS in modeling flow split in hot leg and steam generator tubes.

MELPROG/T~C Based en COMMIX results, th* antira RCS is modeled for TMLB* sequences.

All important phenomena will be included.

SCDAP/RELAPS Based on COMMIX results, th* antira RCS is modeled for TMLB* sequences prior to vessel failura.

Results will be compared with th* MELPROG/TRAC calculations.

Analyses and simple experiments to determine the RCS structural integrity based on th* temperature and pressur* loading calculated by both HELPROG/TRAC and SCDAP/RELAPS.

An estimated uncertainty band of the structur* temperatur* ~ill b* included in the analyses.

Status 8/84 3/85 1/86 1/86 8/86

'186 3/87 3/87 3/87

--~--------------------------------------------------- *----------------

Data shown is for first calculation completed.

More calculations will follow if deemed necessary.

COOCLUSIOO RCS tit\\1UPAL CIRQJLATICJ~ IS QJRREMTLY BEHKJ SlUDIED.

NRC REOOHZES 1lf IMPORTMKE (f THIS ISSUE AND ~

RESEARQI PRCX3RPl'lS IN PLACE TO ADDRESS IT I ~RJ ADEQUA1E FUNDHJG MJST Pf COITINUED AND 1ECHNICAL EXPERTISE MUST BE MAINTAINED AT KEY LAOOPATORIES,

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