ML20125B148

Followup Part 21 & Deficiency Rept Re Failure of General Motors Corp Camshaft Bearing Support Bracket on Diesel Generator 2G003.Components Replaced & Retorqued & Front Bolt Holes on Support Bracket Enlarged

ML20125B148
Person / Time
Site:	San Onofre
Issue date:	05/15/1985
From:	Haynes J SOUTHERN CALIFORNIA EDISON CO.
To:	Martin J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
References
REF-PT21-85 NUDOCS 8506110330
Download: ML20125B148 (2)

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h Southern California Edison Company SW SAN ONOFRE NUCLE AR GENER A TING ST ATION P.o. sox 12e S AN C LEMENT E. C A LIFORNI A 92672 .

. J. G. H A Y N E S ' "

TELEPHONE

.r.1,0N AN.oER May 15,1985 ,,,,,,,,.,,,,

U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region V 1450 Maria Lane, Suite 210 Walnut Creek,- California 94596-5368 1

' Attention: Mr. J. B. Martin, Regional Administrator

Subject:

Docket No. 50-361 Follow-up Report: Diesel Generator Camshaft Bearing Support Bracket Failure San Onofre Nuclear Generating Station, Unit 2

References:

1. SCE 10 CR 50.5b(e) Report to the NRC, Region V, dated September 1, 1981, Diesel Generator 2G003, Engine No. 2, Camshaft Bearing Support Bracket Failure

2. Bechtel 10 CFR 21 Report to the NRC, Region IV, dated September.15, 1981, same subject The referenced reports, submitted pursuant to 10 CFR 50.55(e) and 10 CFR 21, respectively, concerned a failure of a camshaft bearing; support bracket on Unit 2 Diesel Generator 2G003 in 1981. This letter provides follow-up information on the cause and corrective actions related to this condition.

In 1981, during preoperational testing, it was discovered that the rear end camshaft bearing support bracket and several associated bolts on the left bank of 2G003, Engine No. 2 were broken. The cause of tho failure was diagnosed to be improper torquing of the mounting bolts. Corrective action taken was to replace the broken components, and to retorque the bolts within manufacturer's specifications. However, on November 22, 1984, during scheduled six year maintenance activities, the same type of failure was discovered again on 2G003.

Investigation of the November 1984 failure revealed that the actual cause was that the endsheet bolt holes for the cam bearing support bracket were milled too high. This caused misalignment of the bracket, which, over a period of time, caused the bracket and bolts to break due to cyclical stress induced by the cam rotation. The problem was corrected, with approval from the manufacturer's representative, by enlarging the front bolt holes on the

camshaft bearing support bracket, replacing the broken components, and realigning the camshaft within vendor specifications.

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MR.' J. ' 8. MARTIN . . The diesel generator was never inoperable as a result of this condition. No

- evidence of this condition has been discovered on any other Unit 2'or 3 engines during-various maintenance activities. The equipment manufacturer, General Motors Corporation, is being notified by the SCE Quality Assurance

' Organization under separate correspondence.

If you have any questions,'please contact me. -

Sincerely, K Ag-/m cc: F. R'._Huey (USNRC 3enior Resident Inppector, Units 1, 2 and 3)

J.' P. Stewart (USNRC Resident-Inspector, Units 2 and 3)

- Institute of Nuclear Power Operations (INP0) -

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