ML20078L896

Ro:On 941101,DG 2A Invalid Failure Occurred.Problem Isolated to Failed 125 Volt Dc Relay on Instantaneous pre-position Circuit Board.Subj Circuit Board Will Be Replaced W/New Design During Next Unit 2 Refueling Outage

ML20078L896
Person / Time
Site:	Byron
Issue date:	11/21/1994
From:	Schwartz G COMMONWEALTH EDISON CO.
To:	Martin J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
BYRON-94-0459, BYRON-94-459, NUDOCS 9412010197
Download: ML20078L896 (2)

Text

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Byron. Illinois 61010 November 21, 1994 LT: BYRON 94-0459 FILE: 2.07.400 Mr. John Martin Regional Administrator Region III U.S. Nuclear Regulatory Commission 801 Warrenville Road Lisle, Illinois 60532-4351

SUBJECT:

Byron Unit 2 Operating License NPF-66, Docket No. 50-455 Reporting of Emergency Diesel Generator Failures

Dear Mr. Martin:

This report is submitted in accordance with Byron Station Unit 2 Operating License NPF-66 Appendix A, Technical Specification 4.8.1.1.3, Reporting of-Diesel Generator Failures.

The attached report addresses one invalid failure experienced on the 2A Diesel Generator due to a degraded ability to manually centrol generator output voltage. The criteria to determine valid and invalid tests and failures is in accordance with Section C.2.e of Regulatory Guide 1.108, and as such does not affeet the testing requirements established in the Byron Technical Specifications.

l If you have any questions, feel free to contact Dave Baran (ext. 2050) of the i

Systems Engineering Department.

Sincerely, 1 T. / , -

A/ scT2 G.K. Schwartz Station Manage

~ Byron Nuclear Powir Station GKS/ DAB /cib 14ttachments cc: Byron Station NRC Senior Resident Inspector U.S. IRC Document Control Desk, Washington,.D.C INPO Record Center Comed Distribution List 20001r rd

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9412010197 941121 PDR S

ADOCK 050004S5 PDR

l DIESEL GENERATOR 2A INVALID FAILURE NOVEMBER 1, 1994 l

• On November 1, 1994, manual. voltage control was lost while attempting to l synchronize the 2A Diesel Generator (DG) to its associated ESF bus during a  !

monthly surveillance test. DG output voltage remained constant at l approximately 4160 volts-despite several attempts to adjust voltage locally and remotely The DG was shutdown and declared inoperable after initial troubleshooting efforts were unsuccessful at identifying the problem.

Subsequent troubleshocting focused on all possible inputs to the voltage regulator. The source of the problem was isolated to a failed 125 VDC relay on the Instantaneous Pre-Position circuit board. This circuit board establishes the demand for an output voltage of 4160 volts during an automatic start of the DG on an ESF bus undervoltage or Safety Injection signal. The circuit board was replaced with an upgraded model and the DG was declared operable after the satisfactory completion of the monthly surveillance test.

This DG failure was considered invalid based on a previous 10 CFR 21 applicability evaluation performed in response to failures of the 125 VDC relays on the Instantaneous Pre-Position circuit board. This evaluation determined that the failure of the 125 VDC relay did not adversely affect the 2A DG's ability to perform its design function. The relay failure results in a contact closing on the circuit board which places the voltage regulator in the emergency operating mode. If the safety function of the 2A DG was required, the voltage regulator would have had the proper reference voltage for isochronous operation, and the DG would have performed its safety function. Byron Station 1A, 1B, and 2A now have new Instantaneous Pre-Position circuit boards with an improved circuit design provided by NEI Peebles - (generator manuf acturer) . The 2B DG Instantaneous Pre-Position circuit board was replaced in 1992 with the old design and will be replaced with the new design during the next Unit 2 refueling outage.

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