ML20086H931

DG Special Rept PIR 2-M91-0190:on 911107,large Cooling Water Leak Developed in DG 2A After Running at Full Load for 12 Minutes.Caused by Failure of Doughnut Shaped Rubber Seal Between Cylinder Head & Engine Block.Seals Discarded

ML20086H931
Person / Time
Site:	Mcguire
Issue date:	12/05/1991
From:	Roberts R DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
PIR-2-M91-0190, PIR-2-M91-190, NUDOCS 9112100184
Download: ML20086H931 (3)

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,. Duke hwer vmpany T C of<wrm kkCuire helear Generation Department lice 1%ident

!! Tin flagers Ferry ? wad (h!G01A) (704)hi3-18%

^ iluntersvil!*, NC ?SuiMyh3 (704M75-4809 F< t DU% ?OWER December 5, 1991 U.S. :(uclear Regulatory Commission Document Control-Desk Washington, J.C. 20555 Subject; McGuire Nuclear Stat ion, L' nit 2 Docket No.. 50-370 Diesel Generator Special Report Gentlemen:

Pursuant-to McGuire Technical Specifications 4.8.1.1.3.c and 6.9.2, find attached.a special report concerning a valid failure of Diesel Generator 2A.

Should there be any. questions, plea se contact Terry Pedersen at

_(704)875 4487.

Very truly yours, r/ngu,If}tC%/((

T. C.'Mc.Neekin NGA/cbl-Attachment xc :- Mr.-S. D. Ebneter Administrutcr, Regior ;-

-U.G. Nuclear Regulat ay i. Sission 101 Marietta St., NW, f,m e 2900 Atlanta, GA-. 30323 Mr.-Tim-Reed U.S. Nuclear Reaulatory Commission Office of Nuclear Reactor Regulation

-Washington, D.C.- 20555 Mr. P. K. Van Doorn NRC Resident Inspector-McGuire Nuclear Station 9112100104-?112 A JL PDR 3

ADOCK 05000370 FDR S{

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4 DUNE POWER COMPANY McGUIRE NUCLEAR STATION Diesel Generator Special Report PIR 2-M91-0190 December 3, 1991 On November 7, 1991, at 1307, diesel generator (DG) 2A developed a large cooling water leak after running at full load for 12 mjnutes during a routine surveillance test (PT/2/A/4350/02A, Diesel Generator 2A Operability Test) . The leak originated under the 4L cylinder head. DG 2A was promptly ren.oved from service and Work Request 146125 was initiated to repair the leak. This run (start attempt 848) was classified as a VALID FAILURE.

This was the first Valid Failure in the last 20 Valid Tests and the third Va d Failure in the last 100 Valid Tests for DG 2A. On a uni + basis, this is he third Valid Feilure in the last 100 Valid Tests of DGs 2A and 2B combined. Surveillance test frequency remainr- monthly per Technical Specification Table 4.8-1 (Diesel Generator Test Schedule).

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was caused by the failure of the " doughnut" shaped r :t 'eal between the cylinder head and the engine block, m ie - o al was installed and a successful operability run was f wm 1 (start attempt 849, 11/8/91, at 0250). Another

,a att '850) was made on 11/8/91, at 1024, to check for f ort hv .eakage. Three other cylinders were observed to hatre a "c '

small amount of leakage through the rubber seals; however, DG operab 11ty was not af f ected. The water seals on these-cylinders were replaced on November 11 and 12, 1991.

It was discovered during the investigation of the cylinder 4L f ailure that two dif ferent thicknesses of the water seals were in the partn drawer. One seal was one-eighth inch thicker and seemed to of a different rubber compound. NAK Engineering and Cons .ints reported a history of leaks with other utilitja recommendeci using the thicker rubber seal. This seal w- 4 durometer EPDM rubber. Therefore, the thicker seals w to aed in all four of the repaired heads,.

A Metallurgical Analysis Report (Sample 1233, 12/1/91) reported that the failed seals were hardened and had lost elasticity with time. The rubber was identified as styrene butadiene (SBR) rather than neoprene or EPDM rubber.

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All of the SBR seals Nero discarded. ~All seals will be

- replacod during the ne::t Unit 1 and 2 refueling outages. They will be replaced-and checked again after three years and an

. appropriato. . periodic ~ replacement frequency will be established.

/ R.M.y w A( k Roberts System Engineering d

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