ML19338C611

Advises That HR Denton Comments in 800717 Issue of Nucleonics Wk Re Partial Scram at 100% Power & Lack of Operator Action Which Could Have Resulted in Core Damage within 30 Minutes.Inconsistent W/Ge Generic ATWS Submittals

ML19338C611
Person / Time
Site:	Browns Ferry
Issue date:	08/05/1980
From:	Sherwood G GENERAL ELECTRIC CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
FN-137-80, NUDOCS 8008180302
Download: ML19338C611 (2)

Text

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GENERAL h ELECTRIC NUCLEAR POWER SYSTEMS DIVISION GENERAL ELECTRIC CCMPANY,175 CURTNER AVE., SAN JOSE, CALIFORNIA 95125 MC 682, (408) 925-5040 MFN-137-80 August 5, 1980 Mr. Harold Denton Director of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Mr. Denton:

The purpose of this letter is to comment on a statcment attributed to you in the July 17, 1980 issue of Nucleanics Week. This article states that had the partial scram at Browns Ferry Unit 3 occurred at 100%

power, the reactor would have dropped to 20% power, and had operator action such as to initiate the standby liquid control system not taken place at this point, there would have been core damage within 30 minutes.

We do not believe this article is consistent with the information provided to your staff by General Electric in generic ATWS submittals and in telephone discussions related specifically to the Browns Ferry event. The article implies difficulties with a partial scram occurring at 100% power independent of the initiating event -- this is not the case. A conservative assessment of reactor power following a Browns Ferry type partial scram from 100% power was provided during a July 3 telecon with the NRC. It was estimated that power would fall below 10%

given 70 control rods remain fully withdrawn following the first scram attempt. At this power level and assuming a vessel isolation, successful completion of the scram within 40 minutes or manual initiation of the standby liquid control system within 10 minutes would have maintained the peak pool temperature below acceptable temperature limits. There would be no fuel damage.

More recent detailed calculations (discussed with your staff on July 24, 1980) confirmed that power following the Browns Ferry partial scram from full power would be less than 10%. Furthermore, in the case of an isolation, pool temperature (assuming 2 RHR loops and the manual standby liquid control system start at 10 minutes) would peak at approximately 135 F. These conditions are relatively mild and should not stimulate a concern for ccre damage.

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G E N E R A L d[) E LE CTRIC Mr. Harold Denton July 25, 1980 Page 2 Clearly, prolonged operator inattention could eventually lead to situations from which core damage scenarios may be postulated. These are unrealistic whan consideration is given to the time available for operator action and existing operating procedures. Operator response at Browns Ferry resulted in complete shutdown well within the time available to prevent core damage or any other adverse consequences should the initiating situation have been an isolation from 100% power.

We hope this information will be useful in giving perspective to a Browns Ferry-type incident. We would be pleased to provide you any additional further assistance if needed.

Very truly yo s,

,1 /4 N

11 nn G. Sherwood, Manager Safety and Licensing Operation GGS: pes /SLP422 cc: Commissioner John Ahearne Dr. M. Plesset (ACRS)

Mr. V. Stello Dr. D. Ross Mr. L. Gifford (GE - Bethesda)

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