ML17339A390

LER 79-035/01T-0:on 791109,based on Reanalyses Prompted by Vendor Notification,Earlier Clad Burst Time & Resulting Change in Calculated Peak Clad Temp for LOCA Transient Indicated.Cause Not Stated

ML17339A390
Person / Time
Site:	Turkey Point
Issue date:	11/23/1979
From:	Schoppman M FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML17339A389	List: ML17339A387 ML17339A390
References
LER-79-035-01T, LER-79-35-1T, NUDOCS 7912130641
Download: ML17339A390 (4)

Text

NRC PORM S44 V<< S NVCLSAR RSGULATORY COMMISSION n.TTl LICENSEE EVENT REPORT CONTROL BLOCK: I I 'Ol (PLSASS PRINT QR TYPS ALL RSOVI RSO INPORhIATlON) 3' Q~rl I

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0 k REPORTABLE OCCURRENCE 250-79-35 LICENSEE EVENT REPORT PAGE TWO Additioaal Cause Descri tion and Corrective Actions:

The Nuclear Regulatory Commission staff met November 1, 1979, with representa-tives of reactor vendors and nuclear fuel suppliers. The purpose of the meeting was to discuss the staff's ongoing evaluation of the results of tests on electrically-heated fuel assemblies conducted at the Oak Ridge (Tennessee) National Laboratory. NRC indicated that emergency core cooling system analytical codes currently used to evaluate the effects of postulated loss-of-coolant accidents (LOCA) might not be in compliance with NRC regulations. The portion of the codes in question deal with the effects of fue] clad swelling apd rupture and blockage of cooling water.

Subsequent to the meeting, Westinghouse performed a detailed evaluation of the most recent analyses for operating plants and on November 2, 1979, Westinghouse confirmed, in writing, that the impact of the information presented by the NRC has negligible impact on the LOCA analysis results of the plants licensed with the Westinghouse LOCA/ECCS evaluation model. The NRC staff has concurred with this conclusion.

Nowever, as a result of that detailed evaluation, Westinghouse recognized that a non-conservative feature could exist in the Appendix K LOCA analysis with respect to the portion of the calculation related to fuel rod burst.

The potential non-conservative feature of the Westinghouse large break ECCS evaluation model is as follows: The model uses a curve which represents fuel clad burst conditions for clad heatup rates of 25'F/second and greater. The evaluation discussed revealed that heatup rates could be less than 25'F/second.

During the LOCA transient, the fuel clad burst curve establishes the time of clad burst 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. 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.

Therefore, the clad heatup rate prior to burst was determined from the most recent LOCA analyses for those plants licensed with the Westinghouse LOCA/ECCS evaluation model. Plants having heatup rates less than 25'F/second were reanalyzed to ascertain the effect on peak clad temperature. Two plants (Turkey Point Units 3 and 4} were found to require a reduction of 0.01 in Fq to maintain a Peak Clad Temperature (PCT) of 2200'F.

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