ML18219D930

08/06/1976 Letter Temperature of Fluid in Reactor Vessel Upper Head

ML18219D930
Person / Time
Site:	Cook
Issue date:	08/06/1976
From:	Hunter R American Electric Power Service Corp
To:	James Keppler NRC/IE, NRC/RGN-III
References
Download: ML18219D930 (3)

Text

AMERICAN ELECTRIC POVIER Service Corporal on 2 Broadway,¹to York, N.X 10004 (212)422.4800 ROBERT S.HUNTER l icc Prcsidcns.Nuclear Enginccriny Donald C, Cook Nuclear Plant Operating License DPR-58 Docket No.50-315 August 6, 1976 Mr.J.G, Keppler, Regional Director Office of Inspection and Enforcement United States Nuclear Regulatory Commission Region III 799 Roosevelt Road Glen Ellyn, Illinois 60137

Dear Hr.Keppler:

This letter is to confirm our telephone report to your Hr.D.C.Boyd at approximately 1030 hours0.0119 days <br />0.286 hours <br />0.0017 weeks <br />3.91915e-4 months <br /> on August 6, 1976, pursuant to the requirements of Appendix A Technical Specifications and the U.S.Nuclear Regulatory Commission Regulatory Guide 1.16, Revision 4, Section 2.a.At that time we reported that on August 5, 1976 Mestinghouse informed us by telephone of recent developments that bear on the safety analysis of the Donald C.Cook Nuclear Plant which in their judgment constitute unreviewed safety questions.

The first issue involved the temperature of the fluid in the reactor vessel upper head.Past ECCS analyses assumed that the temperature in the upper head was equal to vessel inlet temperature.

Recent model tests, improved analytical techniques and one in-plant measurement suggest this to be in error and a more appropriate assump-tion is that the upper head temperature is 75Ãof the difference between vessel outlet and inlet temperature (added to inlet temperature).

The impact of this finding with reference to the Cook Nuclear Plant is a necessary reduction in Fq to prevent operation at an unaccept-able power level.The current plaht allowable Fq is 1.98.Westinghouse Hr, J, G.Keppl er-2-August 6, 1976 tells us that the current analysis suggests an increase in this value to 2.05, but because of this upper head temperature problem, this analysis will only permit operation with an Fn of 2.02, which is above our current technical specification limit of 7.98.Our actual core peaking factor as determined by current in-core measurements is sub-stantially below the current technical specification limit.Another consequence of this upper head fluid investigation concerns the effects on the steam line break analysis, but Mestinghouse has reviewed the specific Cook case and informed us that this has no effect on Cook Nuclear Plant.A separate problem involves rod bow.Recent results indicate that the rod bow DNB penalty is higher than previously used as a'licensing basis.The combination of this penalty with available margin will result in an estimated reduction of 8Ãin DNBR.To maintain safe operation of the plant this reduction has been incorporated by revising the FgH limit in our in-core flux mapping program.To do this, we have lowered our FgH operating limit by 4X, from 1.5l to 1.45, a value which we are assured by Mestinghouse will compensate for this 85 DNB penalty.Our actual F~as determined by current in-core measurements is less than the modified limit.Mestinghouse advised us that they will keep AEP informed on the results of meetings with the NRC on these matters and the acceptability of the recoranended operating modification.

This letter constitutes the 24-hour written notification, and the written followup report which Section 2.a of Regulatory Guide 1.16, Revision 4, requires to be submitted within two weeks of the telephone notification.

If we receive additional information from Mestinghouse on this subject which relates to our response, we will inform you.Very truly yours, R.S.Hunter Vice President-Nuclear Engineering RSH kb cc: John E.Dolan R.J.Yollen R.C.Callen K.R.Baker P.M.Steketee R.Malsh Gerald Charnoff G.Olson J.H.Hennigan R.S.Keith Plant Nuclear Safety Review Coranittee Director, IE (40 copies)Director, NIPC 4

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