ML20090H540

Discusses Review of RELAP5/MOD 3 Computer Code Error Associated W/Conservation of Energy Equation as Applied to Facility,Per Suppl 1 to NRC Info Notice 92-002 & NRC Verbal Request

ML20090H540
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	03/06/1992
From:	Tremblay L VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BVY-92-29, IEIN-92-002, IEIN-92-2, NUDOCS 9203160123
Download: ML20090H540 (2)

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March 6,1992 1

United States Nuclear Regulatory Commission BW 92-29 NITNi Document ControlDesk-y3 Washington,IX'20555

References:

~ an f Lice.se L 9PR-28 (Docket No. 50-271) u l'.

Le~er, '"".RC to [All Licensees), Infonnation Notice 92-02, dated 1/3N2.

I.etu, i SNRC to {All Licensees], Infonnation Notice 92-02, Supplement 1, dated 2/18/92, d.

Letter, VYNPC to USNRC, FVY 86-61, dated 6/27/86.

U Subject)

RELAP5/ MOD 3 Computer Code Error Associated with the Conservation of a

Energy Equation-

- Dear Sir-Informatica Notice 92-02 [ Reference (b)] was issued by NRC to alert licensees to an error in i

the RELAP5/ MOD 3 computer code associated with the conservation of energy equation. The ermr was considered to be present in all the computer codes in the RELAP5 series. Supplement 1 to information Notice 92-02 { Reference (c)] provided additional information which concluded that the error identified in keference (b) was caused primarily due to application'of RELAP5/ MOD 3 to a situraion for which the code was not intended. - References (b) and (c) requested licensees to L review the information for applicability to their facilities and corisider actions,. as appropriate, co

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avoid similar problems.LHowever, no specific action or written response lwas required by the 4 information notice or the supplement. :

4 x Vermont Yunkee currently has topical teport RELAP5YA in review at NRC. Since :eview of

' RELAP5YA is essentially complete, NRC verbally requested Vermont Yankee to address the impact of References (b) and (c) on RELAP5YA in writing, prior to issuance of te Safety Evaluation and topical report approval by NRC. The purpose of this letter is to comply with NRC's verbal request.

a 50ur review'has shown that the conservation of energy equation in Rl! LAP 5YA is -

fundamentally correct. = However, similar to RELAPS/ MOD 3, the finite difference form of the 4

equation involves approximations, unavoidable in any numerical scheme, that can give erroneous

? results if not understood and mitigated by th: code user. The numerical approximation can result i

in undarstimation of energy in a downstream v olume if the fluid is predominantly in the gas phase j'~

- and undergoes a very steep pressure gradient between adjacent cells. These circumstances are possible if the code is used for containment analysis applications, as in the example provided in e,

Reference (b)J

.RELAP5YA will be used to evaluate the nuclear steam supply system (NSSS) response to LOCA scenarios fer Vermont Yankee as described in the application method provided in Reference

-(d). In this application, the numerical approximation of the energy equation has negligible impact

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March 6,1992 Page 2' on the system response. This is consistent with the USNRC conclusions provided in References (b)'and (c) and is also sup orted by the ccnh assessment calculations performed to justify REIAP5YA application for ermont Yartkee LOCA licensing analysis.

Details of our review have been summarized and provided to code users at YAEC to prevent possible misuse of the code. The review information is on file and available to you on request.

We trust titat this information satisfactorily addresses the subject issue as it pertains to RELAP5YA, and leads to an expeditious iss,iance of the Safety Evaluation Report for this tc,pical repon by NRC If, however, you require additional information, please contact this office.

Very truly yc urs, VERMONT YANKEE NUCLEAR POWER CORPOR ATION s

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Leonard 'A. Tremblay, Jr.

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Senior Licensing Enginee; cc:

USNRC Region I Administrator USNRC Resident Inspector - VYNPS USNRC Emject Manager-VYNPS s

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