ML20128E875

Forwards Request for Addl Info Re Errors in Exxon PWR LOCA Models & Analysis Methods & Possibility of Related Errors at Facility.Info Needed by 850628 to Complete Review

ML20128E875
Person / Time
Site:	Yankee Rowe
Issue date:	05/22/1985
From:	Zwolinski J Office of Nuclear Reactor Regulation
To:	Kay J YANKEE ATOMIC ELECTRIC CO.
References
LSO5-85-05-027, LSO5-85-5-27, NUDOCS 8505290497
Download: ML20128E875 (6)

Text

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.May 22, 1985

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>d Docket No.-50 '

LS05-85-05-027~

I Mr. James A. Kay Senior Engineer-Licensing Yankee Atomic Electric Company

'1671 Worcester Road Framingham, Massachusetts 01701

SUBJECT:

CONFIRMATION OF ECCS CODES Re:

Yankee Nuclear Power Station Recent evaluations of errors in Exxon Pressurized Water Reactor (PWR) Loss of Coolant Accident (LOCA) models and analysis methods raised concerns regarding the possibility of related errors at the Yankee plant.

The enclosed request for additional ~ information identifies the information needed by the NRC staff to complete its evaluation regarding continued compliance with 10 CFR 50.46 for the Yankee plant. We request that you provide your response to the enclosed request for additional information by June 28, 1985.

The reporting and/or recordkeeping requirements contained in this. letter affect fewer than ten respondents; therefore, OMB clearance is not required under P.L.96-511.

Sincerely,

@ signedby:

Joh'n' A. Zwolin'sk'i, Chief Operating Reactors Branch No. 5 Division of Licensing

Enclosure:

Request for Additional Information cc: w/ enclosure-See next page.

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r DOCI'ET NO. 50-29 LOCA APALYSES "nrc:. IEE5, the sta## beca~e avtre of several errors ir the Exxen ri'R w.,m 3-End-re ch ir.Fr'e-severc. ' cr m.

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'.. A cocing error in the T00DEE2 coce.

Thc use c' be:t '"trsfer auccentation facters for local rod teeking

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int nirino vanes, in some Exxen LOCA analyses, even theuch these facters had creviously been found uricceptable.

3.

The discovery of an input error in the St. Lucie 1 LOCA analysis.

2 The validity of the assumption that the Westinghouse-derived K(z) curve was applicable to the Exxon fuel.

Because the Yankee plant utilizes Exxon Fuel, the staff contacted Yankee Atcmic Electric Ccessny (YAEC) on V. arch 22, 1985 and recuested that they evaluate en cc cer "i'" the Exxon LCCA analyses and deterrire these concerns

'. care acclicable to Yar.kee.

Since VAEC per'crns its own LCCA artlysis for '/ar!ee usine rethocs '.thich had previcusly been reviewec and 2?rrovad by the ~ staff, the staff determined that the first three Euen LO:A errors were net cpplicable.

i The renaininc Exxon LOCA analysis error concerned the va'idity o' Exxon's assurptico that the Ecstinghouse-derived El:) curve was applicable to the Exxca. fuel.

The K(2) curve is utilized in the 'iestirchcuse Standard Technical I_

.. Specifications, in conjunction with the maxinum allowable peaking factor (F ),

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_to define allowable peaking factors, or linear heat generation rate (kW/f')

limits, as a function of core elev$ tion. The K(z) curve was developed by Westinghouse, using its approved ECCS eval 6ation model, to assure that the reouirements of 10 CFR 50.46 were satisfied for a range of power shapes.

Exxon assuned that the Westinghouse K(z) curve was applicable to the Exxon fuel and, the-efore, did not perform axial pcwer shape sensitivity studies as required by Section I.A. of Appendix K.

On April 15, 1985, YAEC personnel centacted the staff and informed us of its evaluation of the K(z) curve issue for Yankee. YAEC personnel ' stated that the Yankee Technical Specifications are not based upon a Westinghouse-derived K(z) curve.

Rather, Yankee specific analyses are performed to determine maximum linea'r heat generation. rates, as a function of burnup, which are implemented into the Technical Specifications.

No modifications to the maximum linear heat generation rates are made as-function of core elevation.

In addition, YAEC personnel stated.that the LOCA analyses are performed, using the NRC-approved ECCS evaluation-model, for a chopped cosine axial power shape.

No axial power shape sensitivity studies have been performed for Yankee which support the use of the maximun linear heat generation rate at all core eleva-tions.

It wat mentioned that in topical report XN-75-41A, Supplenent 3, an axial power shape study was performed. The staff has re-examined this report and is unable to conclude that it is applicable to Yankee as it (1) was based upon a 12-foot core height while Yankee has a 7.6 foot core, (2) assumed i

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. decreasing linear heat generation rates as a function of' core height and is

'thereby' inconsistent with the Yankee Technical Specifications, and (3) was

.only analyzed to the end of bypass and not to the time of peak cladding temperature.

Pased upon the above, the staff does not have stfficient inforration to conclude that the Yankee plant remains in conformance with 10 CFR 50.46..

Specifically, its appears that an approved evaluation model may not have been used for the evaluation of ECCS performance which adequately addresses a "rance of power distribution shapes and peaking factors representing power distributions that may occur over the core lifetime" as is required by Section'I.. of Appendix K to 10 CFR Part 50. Also, it appears that the A

. Technical Specifications may not be adequate as the maximum linear heat generation rates are not nodified as a function of core elevation, which is expected to be necessary due to degraded reflooding heat transfer as core elevation increases,.and have not been verified by appropriate LOCA analyses in conformance with Appendix K.

Based upon the above, the staff needs the following information to determine that Yankee remains in conformance with 10 CFR 50.46.

1.

Demonstrate, with reference to appropriate analyses, how the current Yankee LOCA analyses satisfy the requirements of Section I.A. of Appendix K to 10 CFR Part 50.

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. y.- 4 2.

Demonstrate, with reference to appropriate analyses, that the

' current Yankee Technical Specifications assure conformance to'10-CFR 50.'46 for all permissible power shapes.

If the demonstration reouired by questions I and 2 cannot be provided, then

'respohd to the following:

3..

Provide your plans and schedule for performing LOCA analyses which fully conform to the requirements of Appendix K to 10- CFR 50.46.

These plans should discuss the verification and/or modification of your current plant Technical Specifications.

4.

Justify how operation of Yankee, during the proposed time period for analysis given in response to question -3, provides reasonable assurance of compliance to the performance requirements of 10 CFR 50.46 in event of a LOCA.

Provide a description of any administrative controls, if any, you intend to employ in order to assure compliance over this time period.

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