ML20058L921

Advises Commission of Completion of thermal-hydraulic Code Development

ML20058L921
Person / Time
Issue date:	08/06/1990
From:	Taylor J NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
To:
References
TASK-PII, TASK-SE SECY-90-269, NUDOCS 9008090013
Download: ML20058L921 (9)

Text

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.....(. ate........... T.s POLICY ISSUE SECY-90-269 August 6, 1990 gg f_gr:

The Commissionen From:

James M. Taylor Executive Director for Operations

Subject:

COMPLETION OF THERMAL-HYDRAULIC CODE DEVELOPMENT Purcose:

Dur :g the last 15 years, the Office of Nuclear Regulatory Resitrch engaged in research to develop computer codes that modC realistically the response of light water reactors to trarsients and loss-of-coolant accidents (LOCA). The purposa of this paper is to apprise the Commission that the devel opn e:,

program was completed with the release of the final versions of these codes (RELAP5/ MOD 3, TRAC-PFl/ MOD 2, and TRAC-BF1) in June 1990.

iacko'ound:

Thermal :iydraulic systems codes were devloped to provide the staff with an independent c alytical capability for plant transients.

Two versions of the Transient Reactor Analysis code (TRAC) were developed for PWRs (TRAC-PWR) and for BWRs (TRAC-BWR). The TRAC code mcdels the vessel in three dimensions and other fluid systems in one dimension.

Its development dates from 1975. A third code, RELAP, treats the entire system in one dimension. The first RELAP version was released in 1966, while the first TRAC version was released in 1977.

Successive versions of TRAC and RELAP were released approximately every two years, until 1985, reflecting the progress of the continuing code development program which gradually added increased code flexibility, E

modeling detail, and accuracy. The codes have now reached a state of sufficient maturity such that further work would not be expected to yield major gains in accuracy. Thus, no new versions are planned.

Discussion:

1. Staff Use of Codes

- j' The specific functions for which the staff has utilized, and intends to uti'ize, the codes are to:

A Contacts:

NOTE: TO BE MADE PUBLICLY AVAILABLE IN 10 WORKING DAYS l

D. Bessette, RES FROM THE DATE OF THIS PAPER L. Shotkin, RES

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The Commissioners 2

Confirm licensee-analyses by performing audit.

calchlations; Evaluate design and' operational-related issues, including changes to technical specifications, operator guidelines and accident, management' strategies;.

Understand operating reactor' transient events and-their. broad _ implications (includingL "what-if" studies);

Investigate and resolve issues such as BWR stability,-

anticipated transient without scram, pressurized thermal shocki feed _andibleed cooling, etc.;.

-Provide information on' risk-dominant accident sequences; and the early phases of postulated! severe accident scenarios; Evaluate advan'ced LWR' designs.

~2. Code Capabilities The range of conditions that may exist.during plant transients is considerable.

Development of a generalized thermal-hydraulic code to model such states is a large and difficult undertaking.

The following -is illustrative'of the modeling requirements:

Pressure:

I bar to - 200 bar;.

Teaperature:

ambient to 2200Y (to' 5000*F for ~ coupled '

severe accident analysis);

Flow Rate:

stagnant to sonic; and Quality:

subcooled liquid to superheated steam, i

The components;which must be modeled include horizontal and-vertical pipes,' rod bundles (core and. steam generator) vessel (e.g., pressurizer, accumulator, reactor vessel), and pumps.. Complex structures such as flow distributors in the lower plenum and guide structures in the upper plenum _are treated by using equivalent resistance.

3. Code Assessment a.

Experimental data are employed!at three stages in code development:

(1)-in-developing models of physical processes in components of different geometries;_(2) in testing alternative models in the code and.

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The Commissioners-3-

determining that models have been.impismented correctly (developmental assessment); and (3) in 1

evaluating code performance (independent assessment of l validation). The model development is normally performed by experimentalists,and results in' journal publications.

The testing of alternative models.is performed..by the code develo) ment group' utilizing, to

.the extent possible, the tecinical literature.

The third step is carried out external to the: code development group to provide an independent assessment of code performance.

The independence of the -

assessment process is important;to the assurance of

' objectivity and to. establishing credibility.-

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b.

While1RELAPS/ MOD 2:and TRAC-PFl/M001 were reaching completion, RES organized an internatianal program to; i

provide the codes to safety authorities of foreign countries in exchange for independent assessment.

This was effected during 1984-85,. and=the-International Code Assessment Program was~ begun as-a six-year effort to be carried out from 1986-91.

It ~

1 was envisioned that usage of these codes would reveal modeling deficiencies that euld require development of new versions.

This indeea proved to be the case.

A consensus was reached among t'ae-ICAP; code users on i

the nature and -cause of the deficiencies,- and in _

i December 1987 agreement was obtained on'a plan forf development of the final versions of.the ' codes, namely RELAP5/M003 ;and - TRAC-PF1/M002. The code development was carried out during 1988-90 with several ICAP j

participants who will carry out. independent--

assessment.-

'By the end of:1991, the' mission of ICAP will be completed, and a successor program will take effect to maintain a code-users' group focused on:

(1) code applications for. plant. safety analysis; and-(2)' code maintenance. A multilateral agreement-is in preparation for a five-year program which will call for shared funding of code maintenance with 50% to be' provided by RES and 50% by foreign signatories.

Participation is anticipated from most of the ICAP 1

members.

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4. Code Uncerta'inty The most important-issue. encountered in code development is-that of scaling'.. The plants are:large, while the experiments used to develop closure relations am generally-small. The task of: demonstrating that'a cole containing such closure relations is applicable to the full-scale plant is considerable. - To evaluate cooe uncertainty, therefore, a

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The Commissioners-4

- RES developed-a Code. Scalability, Applicability:and Uncertainty Methodology (CSAU) which systematically-addresses these issues.

5.' Code Documentation During the cme development ~and assessment process, it was' recognized thct' improved; practices were required with respect to' doc.amentation and software-quality assura' ice.

Thus, RES established _ requirementslfor documentation to cover the following topics:

code structure,c system models and-solution methods; user guidelines and code input requirements; detailed description of models and correlations;..and documentation of developmental assessment.

Moreover,, formalized software quality-procedures were introduced, and an external audit of the procedures was V

performed. These procedures. are comparable to industry D

requirements.

In addition, code portability was established:

as an objective..Therefore, extensive rewriting was. carried out employing standard FORTRAN.

6. User Convenience The Nuclear Plant Aulyzer (NPA) _provido's interactise-simulation capability with: color graphical display of calculated results.

It-runs the code on a dedicated i

workstation. The NPA ic being utilized on current applications projects such as advanced ~ LWR analysis and quantification of code uncertainty fer small. breakLOCAs in-a Babcock.and Wilcox-design. -The NPA: development, which was completed in May 1990, greatly improves the user interface to the code.

7. External Code Users The NRC codes have come' to. be used'widely,i both domestically; and internationally. Over 100 crganizations in'.the United

' States requested and received the NRC codes including.

. universities, utilities,. vendors, architect engineers, national laboratories, and consulting. organizations.

Seventeen foreign countries are using the codes with_

additional requests in hand 'or expected. A list'of users is, attached as Table -1.

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Coordination:

In its letter of June 15, 1989, the ACRS reviewed the closure plan for thermal-hydraulic code development < and.

endorsed the termination of further major development. The -

Committee stated that further improvements should:be limited to "(a) therdiscovery of.important errors, or:(b) crucial--

new information from the foreignzexperimental~and assessment programs, or the B&W testing program."

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The Commissioners 5'

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Conclusion:==

That the Commission take note of this milestone of completed research.

Beginning this year, plans call for the codes' to be on-a maintenance status. Beginning in-1992, it is-i anticipated that the maintenance will be carried out as part of a joint, irternational cooparative program.

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d' mes M.' T or xecutive Director for Operations

Attachment:

Table 1 DISTRIBUTION:

Commissioners

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OIG GPA l

EDO I

Regional Offices ACRS ACNW ASLBP ASLAF-I L

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j Table 1 user Or:

o' s of the RES Thermal Hydraulic Codes i

Advanced Nuclear Fuel weporation Amdahl Corporation American Electric Power Service Corporation Argonne National Laboratory Arkansas Power and Light ASD International Incorporated Babcock and Wilcox Company i

Baltimore Gas and Electric Battelle Columbus-Laboratory Battelle Pacific Northwest Laboratory 1

BBN Advenced Computers Bechtel Power Corporation l

Black and Veatch T

Boeing Computer Services Brookhaven National Laboratory 3

Carolina Power and Light Company N

Columbia University Combustion Engineering Incorporated i

Commonwealth Edison Company Consumers Power Company Control Data Corporation Cray Research Incorporated Creare,' incorporated Cullen Scientific Systems Corporation Duke Power Company I

Duquesne Light.

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Ebasco Services EG&G Services, Incorporat.!

ENSA Incorporated Electric Power, Research Institute Energy Incorporated ETA Systems Incorporated 1

'Fauske and Associates, Incorporated l

Florida' Power Corporation i

Flour Power Services-Foster wheeler Energy Applications GA Technologies.

'l General. Dynamics i

GPU Nuclear-GRP Consulting, incorporated Georgia' Institute of Technology Gibbs and Hill, Incorporated Gilbert Ccmmonwealth Consolidated i

. Gulf States: Utilities -

Houston Lighting and Power Company l

Illinois Department of Nuclear Safety Impell Corporation-Intermountain. Technologies:

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. Knolls Atomic Power Laboratory.

Middle South Services Incorporated Northeast Utilities L

Northern States Power-3 New York Power AuthorityJ NUS Corporation Nutech Corporation Oak Ridge National. Laboratory l

Ohio Supercomputer Center Pacific Gas and-Electric. Company Pennsylvania State University Power Computing.

Precision Components Corporation Quadrex Corporation Sacramento Municipal Utility District Sandia National Laboratory 1

Sargent and Lundy l

Saul Levy, Incorporated Science-Applications, Incorporated Scientech, Incorporated.

Setpoint Incorporated l

Singer Link-Miles Simulation Corporation-South Carolina Electric ~& Gas-Company Southern Company-Services,. Incorporated Stone and Webster Corporation-TV Electric Teledyne Engineering Services Tennessee: Valley Authority Texas: iM University '

Thermal Hydraulics Incorporated Toledo Edison Company-UCCEL Corporation UMCE. Incorporated United NuclaarL C'>rporation Engineering Services

.UNC Nuclear Industries University of Idaho-

. University of Illinois University of Lowell i

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b University of Maryland:

University:of Michigan-University:of. Missouri Washington Public Power Supply System

, Westinghouse Electric Company Westinghouse-Hanford Company Yankee Atomic Electric Company j

Belgium:

Tractebal-Canada:

~ Atomic ~ Energy of Canada Limi+.ed Ontario Hydro 3

-Finland:

Imatran Voima Oy Technical Research Center of Finland i

France:

Commissariat a-l'Energie Atomique Electricite'de' France Framatone F.R.' Germany:

Gesellschaft fur Reaktorsicherheit-

-i Kernforschungszentrum Karlsruhe:Gmbh i

Siemens AG University of Stuttgart-TUV Mannheim Italy:

.ENEA j

NIRA j

University of Pisa 1

Japan:

Japan Atomic Energy Rese' arch Institute j

Mitubishi Huclear' Fuel Industries Limited.

Toshiba Korea:

Korea Advanced Energy Research Institute Mexico:

' Netherlands:

Energy Research Foundation KEMA-

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. Spain:

Consejo de Seguridad Nuclear Sweden:

Studsvik Energiteknik AB Switzerland:

Paul Scherrer Institut Technical University of Zurich Taiwan:

Institute of Nuclear Energy Research i

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-i United Kingdom:

Atomic Energy.Auth..rity National Nuclear Corporation i

Central Electricity Generating Board:

-Rolls Royce Yugoslavia:

Josef Stefan Institute

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.Cornission of the European Communities Multinational:

International-Atomic Energy Agency i

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