ML20114B955

Special Rept:On 920730,intermittent Operation of Speed Control Response Occurred While Attempting to Synchronize EDG D24 to 4 Kv Safeguard Bus.Caused by Loose Fuse Clip Contacts in 125-volt Dc Circuit.Contacts Tightened

ML20114B955
Person / Time
Site:	Limerick
Issue date:	08/25/1992
From:	Doering J PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9209010013
Download: ML20114B955 (2)

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T.S. 6.9.2 PHILADELPHIA ELECTRIC COMPANY LIMERICK GE.NER ATING ST ATION P. O. DOX A S AN ATOG A, PENNSYLV ANI A 19464 (215) 327 1200 ruv.2000 J. co tet N o, J r.

etaur e.amat e n

.. .... ..... u ~ .ta m a August 25 . 1992 Docket No. 50-353 License No. NPF-85 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555

SUBJECT:

Limerick Generating Station, Unit 2 Special Report for a Valid Emergency Diesel Generator Test Failure

REFERENCE:

Technical Specification Section 4.8.1.1.3 and 6.9.2 This Special Report is being submitted pursuant to the requirements of Technical Specifications (TS) Section 6.9.2 as required by TS Section 4.8.1.1.3. TS surveillance Requirement , 4.8.1.1.3 requires reporting of all diesel generator failures, valid i

or nonva31d, within 30 days. The report is required to include the information recommended in Regulatory Position C.3.b of Regulatory Guide (RG) 1.108, Revision 1, August 1977, " Periodic Testing of Diesel Generator Units used as Onsite Electric Power System at Nuclear Power Plants."

On July 30, 1992, with Unit 2 at 100% power level, plant personnel were performing Surveillanc. Test (ST) procedure ST-6-092-314-2, "D24 Diesel Generator Slow Start Operability Test Run." While the ST procedure was in progress, Operations personnel reported intermittent speed control response while attempting to synchronize the D24 Emergency Diesel Generator (EDG) to the associated 4KV Safeguard bus. The D24 EDG was then secured.

Troubleshooting was conducted on July 30, 1992, to determine the I cause of the intermittent speed control on the D24 EDG, This trouble.T ooting revealed that loose fuse clip contacts in the 125VDC control circuit were the cause of the intermittent speed control.

The fuse clip contacts were tightened and procedure ST-6-092-314-2 was successfully performed on July 30, 1992. The loose fuse clip contacts caused an intermittent loss of the 125VDC control voltage.

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PDR S

ADOCK 0S000353 PDR M21 j 1

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U.S. Nuclear Regulatory Commiss' ion August 25, 1992 Document Control Desk Page 2 After the D24 EDG was returned to service, a circuit analysis revealed that a condition may have existed that could have prevented the L24 EDG output breaker from closing due to the loss of the 125 VDC control circuit. This condition would have prevented the D24 EDG from supplying power to the associated 4KV Safeguard bus. The operability of the D24 EDG could not have been assured following a design basis event such as a safe shutdown earthquake. The D24 EDG would not have been able to provide emergency power to the Division 4 4KV Safeguard bus while it was unavailable for approximately two i during troubleshooting. In the event of an actual loss of I

.t ' power, the three other Unit 2 FDGs would have provided a 4- A,C. power to bring Unit 2 to the safe shutdown condition.

generic implications of this event have been assessed. As a the remaining Unit 1 and Unit 2 diesel generator control s were inspected and confirmed to have no loose fuse clips.

i the first time this type of failure has been observed on the ja (8) EDGs at Limerick Generating Station and no further action regarding the fuse clips is planned at this time.

The D24 EDG failure was classified as a valid failure using the guidance of RG 1.108, Revision 1, August 1977, Section C.2.e(6).

Because this event is the first valid failure for the D24 EDG, the l ST procedure frequency is not required to be changed. This conforms  ;

with TS Table 4.8.1.1.2-1. I If you have any questions, please contact Mr. Gil J. Madsen at (215) 327-1200.

Sincerely, e s

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cc: T. T. Martin, Administrator, Region I, USNRC

T. J. Kenny, USNRC Senior Resident Inspector, LGS  !

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