ML18136A234

LER 79-032/01T-0:on 791109,notified by Westinghouse of Possible Nonconservative Feature Re Fuel Rod Burst in App K LOCA Analysis.Earlier Clad Burst Caused by Reduction in Heatup Rate.Facility Has Sufficient Margin in Model

ML18136A234
Person / Time
Site:	Surry
Issue date:	11/21/1979
From:	Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML18136A233	List: ML18136A232 ML18136A234
References
LER-79-032-01T, LER-79-32-1T, NUDOCS 7911290367
Download: ML18136A234 (3)

Text

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (7-77) .,

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I During a recent reanalysis by Westinghouse, a non-conservative feature con] d exist in the Appendix K LOCA analysis with respect to the calculation related to fue]

~ rod burst. The fuel clad burst curve is dependent on the clad heatup 'rate prior ta

[Im burst and a reduction in heatup* rat~ (<25°F/second) causes earlier clad burst. This event is reportable in accordance with Technical Specification 6.6.2.a.8. The health_~

safety of the general public were not affected by this event.

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j Heatup rate prior to burst was determined from most recent LOCA/ECCS analysis. It was ITIIJ I determined that Surry has sufficient margin in the model to allow opera ti on wi tbout a I OTIJ ITTIJ 7 8 9 80 FACILITY METHOD OF A STATUS  % POW::R OTHER STATUS DISCOVERY DISCOVERY DESCRIPTION ~

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.i ATTACHMENT: Page 1 of 2 SURRY POWER STATION DOCKET NO: 50-280 REPORT NO: 79-032/0lT-0 EVENT DATE: 11/9/79 TITLE OF EVENT: Fuel Rod Burst Analysis

1. DESCRIPTION OF EVENT On November 9, 1979, VEPCO was notified of an unreviewed safety question by Westinghouse Electric Corporation. The unreviewed safety question con-cerned a potential non-conservative feature of the Westinghouse ECCS large break evaluation model which could affect the peak clad temperature calcu-lated for the LOCA transient.

The event is reportable in accordance with Te.chnical Specification 6. 6. 2. a. 8.

2. PROBABLE CONSEQUENCES/STATUS OF REDUNDANT SYSTEMS The Westinghouse evaluation revealed that heatup rates could be< 25°F/second.

During the LOCA transient, the fuel clad burst curve establishes the time of clad burs and (since the clad temperature .and the pressure differential across the clad are changing throughout the LOCA transient) the post-burst conditions of the clad. It was determined that sufficient margin existed in the analysis such that the health and safety of the public were not affected.

3. CAUSE The potential non-conservative feature of the Westinghouse large break ECCS evaluation utilized a model which uses a curve that represents fuel clad burst conditions for clad heatup rates of> 25°F/second. The fuel clad burst curve is dependent on the clad heatup rate prior to burst and a reduction in heatup rate causes earlier clad burst. A shift in clad burst time can affect the peak clad temperature (PCT) calculated for the LOCA transient.

4. It1MEDIATE CORRECTLVE ACTIONS Since the cuu.rent Surry LOCA-ECCS analyses exhibited heatup rates less than 25°F/sec., a specific reanalysis was performed to ascertain the effect on PCT £or the Surry Unit 1 analysis. It was determined that sufficient margin existed to the PCT limit of 2200°F for Surry Unit 1 to offset the small effect of using a more appropriate burst curve.

5. SCHEDULED CORRECTIVE ACTION Westinghouse determined that Surry has margin available in the model to allow operation without a reduction in FQ.

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e ATTACHMENT: Page 2 of 2 SURRY POWER STATION, UNIT 1 DOCKET NO: 50-280 REPORT NO: 79-032/0lT-O TITLE OF EVENT: Fuel Rod Burst Analysis

6. ACTION TAKEN TO PREVENT RECURRENCE Since the Westinghouse LOCA/ECCS evaluation for Surry has been completed, no further action is required to prevent recurrence.

7. GENERIC IMPLICATIONS This event was a Westinghouse identified generic item. However, since Surry Unit 2 is not currently operating, a re-evaluation has not been performed. A re-evaluation of the Surry Unit 2 will be performed prior to Unit 2 startup.