ML19329B282

Deficiency Rept Re Diesel Generator Sequencer Design.During Review of Safety Features Actuation Sys,Safety Actuation Signal to Emergency Diesel Generator Found Blocked.Loss of Offsite Power Signal to Be Added to Reset Logic

ML19329B282
Person / Time
Site:	Davis Besse
Issue date:	01/21/1977
From:	Roe L TOLEDO EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19329B281	List: ML19329B282
References
NUDOCS 8002040675
Download: ML19329B282 (2)

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January 21, 1977

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Serial No. 189 Docket No. 50-346 Mr. James G. Keppler

.- Regional Director Region III Office of Inspection and Enforca=ent U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137

Dear Mr. Keppler:

This letter is submitted in accordance with 10 CFR 50.55(e) as a final report regarding the Davis-Besse Nuclear Power Station Unit 1 diesel-generator sequencer design deficiency, which was reported by telecon between our Mr. E. C. Novak and your Mr. D. Hayes on December 23, 1976.

Description of the Deficiency The sequencer, as part of the Safety Features Actuation System (SFAS),

receives input cignals from the undervoltage relays of the essential

• 4.16KV bus and from the emergency diesel-generator (EDG) start logic of the SFAS. Both signals are necessary for the sequencer to be turned on, and the bus voltage returning to normal (EDG on line) will start the timing sequence. If a loss of offsite pouer does not occur concurrent with a loss of coolant accident, the EDG will be started, but the sequencer will not operate. To stop the EDG at this point, the Safety Actuation (SA) signal to start the EDG must be blocked. A loss of offsite pouar will restart the EDG. .

• During review of the SFAS sequencer logic, it was determined that once the SA signal to the EDG was blocked and a subsequent loss of offsite power occurred, the EDG would start, but the sequencer would not receive an SA signal. This would cause the essential pumps, started by the SFAS, not to restart once they had been cleared f rom the bus by an undervoltage condition. Only af ter the block to the SA signal was removed could the sequencer be started and the pumps be restarted.

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THE TOLEDO EDISON COMPANY ECISON PLAZA 300 MACISON AVENUE TOLECO, CHtO 43652 JAN 2 61977

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• o Corrective Action Taken After a review of the circuits affected, it was determined that the sequencer must be operated when a loss of of fsite power occurs af ter a LOCA. At that ti=e, most loads including essential pumps are tripped (clearing the bus). Each of the pump circuits affected involves an anti-pumping scheme on the associated circuit breaker. The operation of this circuit is such that after the circuit is tripped, the anti-pumping relay must be dropped off before the closing coil circuit of the breaker can be re-energized. When the sequencer is turned on, all SA signal will be blocked, this will allow the anti-pumping relays to be reset. As the sequenser is run, it.will unblock the SA signals in sequence, allouing the pumps to be re-started.

To insure that the sequencer is available whenever a loss of of fsite power occurs, a icss of 'off site power signal will be added to reset the

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SA logic which transmits a signal to the sequencer. This will also unblock the SA signal to the EDG. This reset signal will not have any affect on the SFAS logic if it is either not blocked or a LOCA condition does not exist.

All equipment modifications will be done under approved procedures and the equipment will be retested after the modification to insure that it will operate as per the design criteria.

Safety Implications The correction of the deficiency as described above prior to the operation of the facility assures that the health and safety of the public are not j eopardized.

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Yours very truly, efG YL cp e/2-3

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cc:

Dr. Ernst Volgenau, Director

• Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, D.C. 20555

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