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IllTERIll REPO?.T -

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UC Rcsearca anc ~echnicakccession no.Assistance Report.

Contract Prograa or Project Title: SSC code Development & Validation

Subject of this Document: SSC Project Highlights for March

Type of Document: tionthly Highlight Letter

Author (s): A. K. Agrawal/ R. J. CerboneDepartment of fluclear EnergyBrookhaven flational Laboratory

"Upton, flew York 11973,

Date of Document:.

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Responsible !!RC Individual Dr. Robert T. Curtis, Chief

and llRC Office or Division: Analytical Advanced Reactor Safety Research BranchDivision of Reactor Safety ResearchU.S. fiuclear Regulatory CommissionWashington, D.C. 20555

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This document was prepared primarily for preliminary or internaluse. It has not received full review and approval. Since theremay be substantive changes, this document should not be consideredfinal.

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~ Brookhaven !!ational LaboratoryUpton, llY 11973

Associated Universities, Inc.for the

U.S. Department of Energy

Prepared forU.S. Iluclear Regulatory Comission

Uashington, D. C. 20555Under Interagency Agreement EY-76-C-02-0016

IIRC Fli! !!o. A- 3015-8

It!TERIM REPORT .

[RC Researc1 anc Tec1nical7905 210 YA7 mo e 'a

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Assistance Report o

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SSC Project Highlights

for

March 1979

N RC Researca anGechnicalAssistance Report

PROGRAM: SSC Code Development and Validation

A. K. Agrawal, Group Leader

Code Development and Verification GroupEngineering and Advanced Reactor Safety Division

Department of Nuclear EnergyBROOKHAVEN NATIONAL LABORATORY

Upton, New York 11973

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This is the monthly highlights letter for (1) The SSC Code Developmentand (2) SSC Code Validation Programs, Fast Reactor Safety Assessment, for themonth of March, 1979. These programs are covered under the budget activitynumber 60-19-20-01. Only major accomplishments are noted in this letter.

A. CODE DEVELOPMENT (A. K. Agrawal)

I. SSC-L Code (J. G. Guppy)

1. Modifications to Heat Transfer in Fuel Structure (J. G. Guppyand R. J.Kennett)

Changes were incorporated into SSC to give the user more flex-ibility in the specification and importance of structural materialassociated with any core channel. For each different assembly / rodtype, the user must now specify wire-wrap diameter, hex-can flat-to-flat distance, and hex-can thickness. On a channel-by-channelbasis, the user can very the importance assigned to the hex-can byspecifying a fractional area coefficient (0 to 1.0). The wire-wrapmay be neglected if desired by setting the diameter to zero. Therequired coding changes were tested c.nd debugged.

2. Plant Protection and Control Systems (M. Khatib-Rahbar, E. S.Srinivasan and R. J.Kennett)

An input data verification procedure for the PPS-PCS data hasbeen incorporated. This will ensure that a consistant set of datais provided before any calculation is started.

The steam generator system feedback control models were alsocompl eted. They include models for the feedwater, turbine, andturbine bypass flow controllers for both recirculation andonce-thru designs.

We are now '.n the process of preparing a consistant set of reac-tivity feedback coefficients for simulation of typical operationaltransients by applying SSC-L for a five channel, CRBRP represen-tation.

3. Sodium Boiling (R. Pyare and T. C. Nepsee)

A pipe rupture transient with reactor scram was run up to 20seconds with the single phase version of SSC-L. The coolant tem-perature at the top of the active core in the peak assembly ex-ceeded the saturation temperature between 1.3 and 5.5 seconds. Theboiling version of SSC-L was successfully run up to 6.8 seconds forthe identical case. The formation and quenching of bubbles was in-dicated from 1.3 to 6.8 seconds. To see further results, thetransient is being restarted from this point. Qualitatively, theduration of boiling prediction by the boiling code is longer thanthat predicted by single phase version.

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4. DHX Module Interfacing (W. L. Weaver III)

The interfacing of the DHX modules with the remainder of the -

SSC-L code was completed. Steady state and pump coastdowntransients were successfully run to debug the new version of thecode. While interfacing the DHX modules with the SSC-L code, it wasdiscovered that the logic in the intermediate sodium hydraulicsexpects the tertiary loop (steam generator) to contain a super-heater.

5. Steam Generator (W. L. Weaver III)

Changes to the SSC-L code have been made and debugged so that aonce-thru steam generator (one containing no separate superheatermodule) can be simulated. These changes involve the way in whichthe feedwater flow rate is calculated and controlled. Also,changes have been made to the code so that the user can specifythe feedwater flow rate as a function of time thru input data.This option approximates manual feedwater control. A provision hasbeen also made in the new feedwater algorithm so that the feedwatercontrol will switch from automatic to manual control at a user-specified time.

6. Application of SSC-L

The SSC-L code was run to simulate a natural circulation tran-sient in CRBRP for up to 1800 seconds of simulation. This run took1785 seconds of CPU time on a CDC-7600 at an approximate cost ofabout $250.

7. CRBRP Data Needs

A meeting with the Westinghouse Advanced Reactors Division hasbeen arranged for procuring more detailed design data for CRBRP.This meeting is scheduled for April 10, 1979 at the Waltz Mill site.

II. SSC-P Code (I. K. Madni)

1. Initialization (I. K. Madni and E. G. Cazzoli)

A closer look at the steady-state results revealed that the coreoutlet temperature from core coolant calculations did not match thatobtained from hot pool energy balance. This discrepancy was tracedto two errors in the code: (1) reactor power was obtained fromplant balance (this is valid only for loop-type LMFBRs), and (2)normalized axial power fraction in the coolant channels were incor-rectly calculated in the presence of a lower fission gas plenum.Both these errors have been corrected, and now perfect matching ofcore outlet temperature is obtained.

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2. Transient (I. K. Madni and E. G. Cazzoli)

Hot pool energy equations have been written incorporating the2-zone stratification model used in SSC-L. The mass of sodium, aswell as the heat transfer area with the barrier, will be calculatedfor each zone during transient computations. Mass heat capacitiesof barrier, roof structure and lower internal structure have beenestimated.

Debugging of transient hydraulics is continuing.

3. Code Management (S. F. Carter)

In the past month, work on the pool version of SSC included modi-fications and extensions to the data read and verification portionsof the steady state code.

III. SSC-S Code (W. L. Weaver III)

1. Assessment of Interassembly Heat Transfer (G. J. Van Tuyle)

To aid in assessing the effects of interassembly heat transfer,the ENERGY 2 and ENERGY 3 code have been loaded in the BNL system. Atest case has been run using the ENERGY 2 code, and the results areclose enough to those reported in the code manual to indicate accur-ate reproduction, when taking into consideration the numerical trun-cation differences between IBM (MIT) and CDC (BNL) machines.. Verifi-cation of the ENERGY 3 code reproduction has been complicated due tothe long running time required. Some effort is being made to opti-mize the code before making further test runs.

2. Intra-Assembly Transverse Heat Transfer (J. E. Meyer*)

An assessment of the intra-assembly transverse heat transfer wa'smade using a simplified, slab geonetric representation. While thiswork is continuing, some preliminary results have been obtained.These are: (1) axial conduction can be neglected for flows with as-sembly Reynolds number as low as 36 for fuel and as low as 21 forblanket assemblies, and (2) the blanket assembly reduction of hotchannel factor caused by transverse heat transfer is appreciable atfull flow and any major further reduction occurs only below 10% flow.

B. CODE VALIDATION (A. K. Agrawal)

1. Modeling of FFTF During Natural Circulation (L. G. Epel)

Work has begun on preparing an input deck for SSC-L runs to model theFFTF natural circulation tests. The first case to be simulated will bea steady-state transient run at fractional core power. This should allowfor refinement of the input data prior to simulating the second case,which will be a transient involving a LOEP from full power operation.

" Consultant, M.I.T. -3-

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The main effort so far has been in obtaining the parameters for thepiping and heat exchangers in the primary and secondary loops of theFFTF. Many of the parameters for the vessel intervals have been obtainedpreviously, although additional work will be required for the naturalcirculation studies. Similarly, most of the modeling of the DHX has alsoalready been done but not yet tested for the particular cases to besimul ated.

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DISTRIBUTION

R. T. Curtis, NRCW. Gammill, NRC 3 copiesW. Y. Kato, BNL - IB 5 copiesC. N. Kelber, NRC*H.J.C. Kouts, BNLP. M. Wood, NRC 3 copiesRSP Division Heads, BNLRSP Group Leaders, BNLDivision of Technical Information

and Document-Control * 2 copies

*via W. Y. Kato's Office

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