ML19329A796

RO NP-33-77-74:on 770907,decay Heat Suction Valve DH-12 Closed During Switching from Normal to Alternate Power Supply for Valve.Caused by Design Deficiency in Interlock/Control Circuit.Wiring Change in Process

ML19329A796
Person / Time
Site:	Davis Besse
Issue date:	10/04/1977
From:	Batch S TOLEDO EDISON CO.
To:
Shared Package
ML19329A788	List: ML19329A787 ML19329A796
References
NUDOCS 8001150695
Download: ML19329A796 (2)

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TOLEDO EDISON COMPANY

a. DAVIS-BESSE UNIT ONE NUCLEAR POWER STATION

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SUPPLEMENTAL INFORMATION RR,LE_R_NP-33-77-74 DATE OF EVENT: September 7, 1977 ,

l FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Reactor Coolant flow less than 2800 gallons per minute.

Conditions Prior to Occurrence: Iha plant was in'Moda-5, with Power (MWT) = 0 and Load (MWE) = 0. Reactor Coolant Systustpressure a u -arely 100 psig.

Description of Occurrence: At 0530 hours0.00613 days <br />0.147 hours <br />8.763227e-4 weeks <br />2.01665e-4 months <br /> on September 7, 1977, while switching the normal power supply (MCC E113) for the Decay Heat (DH) suction motor operated

.__ . valve DH12 to the alternate power supply (MCC Fila), DH12 closed. The Reactor ._

Operator re-opened the valve as soon as it stroked closed. When DH 12 closed . _

to prevent a 2800 GPM flow rate, Decay Heat Pump 1-1 was started which took suction from the Borated Water Storage Tank. The Decay Heat Flow was less than 2800 GPM for only a few seconds, but for that-time the station was in violation of Techni-cal Specification 3.1.1.2.

When DR Pump 1-2 was again recirculating greater than 2800 GPM, DH Pump 1-1 was stopped. Pressurizer water level had increased from 255 inches to 285 inches due to the water that was pumped from the. Borated Water Storage Tank by DH Pump 1-1.

Designation of Apparent Cause of Occurrence: The apparent cause of this occurrence is a design problem in the circuit which interlocks and controls the motor operator of DH12. This caused the valve to close during the transfer of power from its normal to its alternate power supply. The closure of the suction valve caused p decay heat-flow to be less than 2800 GPM.

Analysis of Occurrence: There was na dangar to.the health sud safety of the public or to station personnel. Decay East flour was . lass than 2800 GPM for only a few seconds.

l Corrective Action:~ Facility Change Request,77-034 has been approved which requests a control circuit. change to DH 11. A Maintenance Work Order has been written to incorporate this change. Since DH12 is the only suction valve with this wiring arrangement, this wiring change should prevent recurrence.

Failure Data: There have been four previous closures of a DH suction valve,

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NP-32-77-2, NP-32-77-3, NP-32-77-5 and NP-32-77-9, but none of these were caused  ;

v i by the design deficiency in the control circuit. I

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