ML20092M175

Special Rept:On 950726,valid Failure of E-3 EDG Occurred Due to Dead Spot on Potentiometer Which Affected E-3 EDG Controller Output signal.E-3 EDG Returned to Operable Status Following Motor Operated Potentiometer Replacement

ML20092M175
Person / Time
Site:	Peach Bottom
Issue date:	09/22/1995
From:	Geoffrey Edwards PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9509290089
Download: ML20092M175 (3)

Text

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D N Garrett D. Edwards Plant Manager Peach Bottom Atomic Power Station

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PEC'O ENERGY rem e-ov =ev 1848 Lay Road Delta. PA 17314 717 456 4244 September 22, 1995 1

Docket Nos. 50-277 50-278 Ucense Nos. DPR-44 DPR-56 Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555

SUBJECT:

Peach Bottom Atomic Power Station - Unit 2 & 3 Special Report for a Valid Failure of the E-3 Emergency Diesel Generator on 7/26/95

REFERENCE:

Peach Bottom Atomic Power Station Technical Specification (Tech Spec) 4.9.A.1.2.L and M This Special Report is being submitted as a revision to the report dated 8/14/95 to provide updated information and is being submitted pursuant to the '

requirements of Tech Spec 4.9.A.1.2.M. This Surveillance Requirement requires reporting of all emergency Diesel Generator (D/G) failures, valid or non-valid, within 30 days. This report is required to include the information recommended in Regulatory Position C.3.d of Regulatory Guide (AG) 1.108 " Periodic Testing of Diesel Generator Units as Onsite Electric Power System at Nuclear Power Plants",

Revision 1, August 1977.

On 7/26/95 at approximately 0130 hours0.0015 days <br />0.0361 hours <br />2.149471e-4 weeks <br />4.9465e-5 months <br />, with Unit 2 at 100% power and Unit 3 at approximately 70% power, during the performance of a Surveillance Test (ST),

the E-3 D/G Output Breaker (E-32) tripped open while the cperator was attempting to increase load on the unit. Initial troubleshooting revealed that the E-3 D/G Motor Operated Potentiometer (MOP), used for manually increasing load on the D/G during testing activities, may have had a dead spot, it was believed that the dead spot on the potentiometer affected the E-3 D/G controller output signal thus CCN 95-14083

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'U. S. Nuclear Regulatory Commission Page2 causing the fuel racks to close and the D/G Output Breaker to trip open. At approximately 2312 hours0.0268 days <br />0.642 hours <br />0.00382 weeks <br />8.79716e-4 months <br />, the E-3 D/G was returned to an operable status following MOP replacement and successful D/G testing.

The E-2 and E-4 D/G MOPS were just replaced with a new type MOP during the recent D/G modification outages. The E-1 D/G MOP was just successfully used for testing on 7/25/95. In addition, the E-1 and E-3 D/G MOPS will be replaced with the new type MOP during future modification outages. i The E-3 D/G failure was classified initially as a non-valid failure using the guidance of RG 1.108, Revision 1,1977 and a Special Report was submitted to the NRC on 08/14/95. However, on 9/11/95, based on a review of the failure analysis information, it was determined that this event was actually a valid failure versus a non-valid failure. It was initially believed that the MOP had a dead spot at a point on its resistor that would not adversely affect D/G operation in the emergency mode. However, the failure analysis revealed that the problem was actually associated with a wire connection and not the resistor itself. The wire associated with the MOP output signal was found not to be soldered to its terminal. The wire was inserted in the terminal's hole and wrapped versus soldered. This condition resulted in intermittent contact between the terminal and the wire which caused the fuel racks to close and the D/G Output Breaker to trip open. The terminal is located under a factory sealed cover and is soldered by the manufacturer.

Therefore, efforts are being made to work with manufacturer to resolve this concern. The terminals on the other MOPS have been inspected and were found to be properly soldered.

This failure could have adversely affected D/G operation in the normal and emergency modes, therefore, the E-3 D/G failure is now classified as a valid failure using the guidance of RG 1.108. Because this occurrence was classified as a valid failure and was the first valid failure in the last 100 valid tests, the current surveillance testing interval will remain at once per 31 days which is in conformance with RG 1.108, Revision 1, Section C.2.d.

During this event, the E-3 D/G was unavailable for operation approximately 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />. The remaining D/Gs were operable and would have provided adequate AC power to safety related loads in the event of an actual loss of offsite power.

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CCN 95-14083 1

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'U.' 5. Nuclear Regulatory Commission Page3 If you have any questions or require additional information, please do not hesitate to contact us.

Sincerely, GDE/GAJ:gaj

. cc: R. A. Burricelli, Public Service Electric & Gas R. R. Janati, Commonwealth of Pennsylvania T. T. Martin, US NRC, Region 1 R. l. McLean, State of Maryland W. L. Schmidt, US NRC Senior Resident inspector H. C. Schwemm, Atlantic Electric i A. F. Kirby Ill, DelMarVa l

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l CCN 95-14083