ML20079H139

Forwards Rept on Unit 1 High Drywell Temp, as Committed to During 831121 Meeting & Documented in IE Insp Repts 50-373/83-50 & 50-374/83-53.Drywell Heating Problem in Context of short-term Fixes Addressed

ML20079H139
Person / Time
Site:	LaSalle
Issue date:	12/22/1983
From:	Schroeder C COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20079H087	List: ML20079H121 ML20079H139 ML20079H154
References
7812N, NUDOCS 8401230339
Download: ML20079H139 (2)

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Commonwer.ith Edison

, One First National Plata. Chicago, ilhnoj Address Reply to Post Office Box 767 Chicago. Ilhnois 60690 December 22, 1983 Mr. James G. Keppler ,

Regional Administrator U.S. Nuclear Regulatory Commission 799 Roosevelt Road - Region III Glen Ellyn, IL 60137

Subject:

LaSalle County Station Unit 1 Report on Unit 1 High Drywell Temperature NRC Docket No. 50-373 References (a): LER No. 83-143/OlT-0.

(b): LER No. 83 145/03L-0.

(c): A. B. Davis letter to Cordell Reed dated December 2, 1983, Inspection Report Nos. 50-373/83-50 and 50-374/83-53.

Dear Mr. Keppler:

References (a) and (b) have provided you with initial notifica-tion regarding the apparent Unit 1 drywell high temperature. On November 21, 1983, as documented in Reference (c), Mr. Cordell Reed, et al, met with you and members of your staff. During that meeting Commonwealth

' Edison Company provided you with a briefing regarding this situation. It was requested during that meeting (and documented in Reference (c)) that the licensee " formally identify to Region III those short term actions you will take to address this problem."

The purpose of this letter is to fulfill our commitment by transmitting the enclosed " Commonwealth Edison Company, LaSalle County Station - Unit 1, Report on Unit 1 High Orywell Temperature." The enclosed report addresses the drywell heating problem in the context of short-term fixes to enable Unit 1 restart ~. The corrective actions cannot .

be evaluated without sensible heat input to the drywell, thus plant operation is necessary. It is prudent in such a case to acknowledge that the residual effects of the high drywell temperatures are accelerated thermal degradation of electrical cables and equipment, including mechanical snubbers. The cables and equipment have remaining qualified life characteristic of the materials of which they are made. The degrading mechanisms are incipient rather than catastrophic (excepting water spray e f fects) . This was verified in the LaSalle drywell high temperature experience reported here; the safety-related cable and equipment were operational at the time of Unit 1 shutdown af ter having been exposed to overtemperatures wherein the computed service (and accident) life was only partially consumed.

8401230339 840113 PDR ADDCK 05000373 G PDR -

J. G. Keppler December 22, 1983 This conservatism is inherent in electrical equipment because approximately 90 percent of the projected degradation is assignable to LOCA accident exposure whereas approximately 10 percent of the degradation is assignable to normal service conditions. Conservatism is also inherent in the physical degradation mechanisms involved because they are usually molecular involving electron bonding or are atomic in nature involving displacements and cleavage planes. Arrhenius methodo-logy _ utilized to estimate lifetime incorporates activation energies in the equations which predict life; conservative regression analysis is used to derive activation energies such that mean activation energies are not used, but minimum bounding values are used to cover natural variations in the material. From these conservative calculations come lifetimes representative of the adverse combination of materials and '

technical observations. Actual life demonstrations conventionally exceed the predicted minimal life. '1 For the above reasons and based on the enclosed report, the immediate restart of LaSalle Unit 1 under normal plant procedures, operating it under existing technical specifications, monitoring the drywell thermal characteristics assignable to locations with safety related equipment, and making the future evaluations of the effectiveness of installed short term fixes and remaining equipment lifetimes, all add assurance for continued safe operation of LaSalle Unit 1.

To the best of my knowledge and belief the statements contained herein and in the attachment are true and correct. In some respects these statements are not based on my personal knowledge but upon infor-mation furnished by other Commonwealth Edison and Contractor employees.

Such information has been reviewed in accordance with Company practice

'and I believe it to be reliable.

l If there are any further questions in this matter, please contact j this of fice.

l Very truly yours, t

i C. W. Schroeder /k2.2./93 Nuclear Licensing Administrator im Enclosure cc: NRC Resident Inspector - LSCS 1

7812N

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