ML19329B621

RO NP-33-77-06:on 770514,while Removing Bracket from Safety Features Actuation Sys Channel 2,loss of Y2 Bus Occurred Tripping Channel.Caused by Personnel Error & Design Problem. Personnel Blocked Actuated Components

ML19329B621
Person / Time
Site:	Davis Besse
Issue date:	06/14/1977
From:	Batch S, Lingenfelter J TOLEDO EDISON CO.
To:
Shared Package
ML19329B545	List: ML19329B544 ML19329B621
References
NUDOCS 8002050738
Download: ML19329B621 (3)

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- TOLEDO EDISON COMPMW A DAVIS-BESSE UNIT ONE NUCLEAR POWER STATION SUPPLEw. ENTAL I'* FORMATION FOR LER NP-33-77-6 DATE OF EVENT: May 14, 1977 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: At 0452 hours0.00523 days <br />0.126 hours <br />7.473545e-4 weeks <br />1.71986e-4 months <br /> on May 14, 1977, Safety Features Actuation System (SFAS) Channel 2 and Reactor Protection System (RPS) Channel 2 tripped because of blown fuses. At 0504 hours0.00583 days <br />0.14 hours <br />8.333333e-4 weeks <br />1.91772e-4 months <br /> while trying to replace the fuses, SFAS Channel 1 and RPS Channel 1 were accidentally tripped causing an SFAS actua-i tion-l Conditions Prior to Occurrence: The plant was in Mode 5.

Description of Occurrence: An Instrument and Contr61 (I&C) Mechanic shorted out a fuse in the Auxiliary Shutdown (ASD) Panel while re=oving a bracket. This caused Inverter YV2 to trip and subsequer.t loss of Y2 Bus. The fuse on Y2 Bus that feeds the ASD Panel did not blow; the 6 amp fuse in the ASD Panel did blow.

The 225 amp fuse at Inverter YV2 also blew, RPS Channel 2 and SFAS Channel 2 then tripped.

( ,jDuring the effort to de-energize SFAS Channel 2 and RPS Channel 2, so that the blown fuses.could be replaced, SIAS Channel 1 was accidentally tripped, thus s'atisfying a two out of four logic which actuated incident levels 1.through 5.

At this time, Source Range Nuclear Instrument (NI) I was out for servicing. Be-cause of the loss of Y2, NI 2 was also lost' in violation of Technical Specifica-tion (TS) 3.9.2. SFAS actuated properly isolating the Decay Hear System from the Reactor Coolant System, stopping RCS recirculation in violation of Technical Speci-fication 3.4.1.

Designation of Aeoarent Cause: While removing a bracket from SFAS Channel 2, an I&C Mechanic dropped it causing a short which tripped the channel. In order to-

replace the blown fuses and restore SFAS Channel 2 to service, an operator was instructed to de-energize SFAS Channel 2 and RPS Channel 2; but he inadvertently removed power from SFAS Channel 1 which cau* sed the SFAS to actuate. Bus Y2 trip has been determined to be due to a design problem by the inverter vendor, Cyberex.

Analysis of Occurrence: Since the SFAS actuated correctly and three out of the four essential power supplies were operable, the event did not result in a threat to the health and safety of the public or to stati,on personnel. Cyberex is currently investigating the problem in YV2 to make design changes to prevent -

1 recurrence.

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TOLEDO EDISON COMPANY '

DAVIS-BESSE UNIT ONE NUCLEAR PO*.T.R STATION SUPPLEMEhTAL INFORMATION FOR LER NP-33-77-6 PAGE 2

Corrective Action

Operator blocked the SFAS actuated components, and returned l plant to normal status. Operator placed Y2 on alternate source and returned Decay Heat Pump to recirculation of the RCS.

i Failure Data: No previous similar events have occurred.  !

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