ML19329B626

RO NP-33-77-07:on 770519 Accidental Loss of 13.8 Kv B Bus Resulted in Loss of Essential Power Supply to One of Four Safety Feature Actuation Sys Channels.Caused by Personnel Error in Switching & re-energization.Components Blocked

ML19329B626
Person / Time
Site:	Davis Besse
Issue date:	06/19/1977
From:	Batch S, Lingenfelter J TOLEDO EDISON CO.
To:
Shared Package
ML19329B547	List: ML19329B546 ML19329B626
References
NUDOCS 8002050742
Download: ML19329B626 (3)

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DAVIS-BESSE UNIT ONE NUCLEAR POWER STATION SUPPLEMENTAL INFOPJ'ATION FOR LER NP-33-77-7 DATE OF EVENT: May 19, 1977 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Accidental loss of a 13.8 KV B Bus resulted in loss of an essential power supply to one of four Safety Feature Actuation Cystem (SFAS) channels. Incorrect restoration action for the SFAS resulted in a trip of a second SFAS channel causing a safety actuation. Loss of essential power supply caused loss of both source range detectors and the SFAS actuation caused loss of decay heat flow.

Conditions Prior to Occurrence: The plant was in Mode 5. Power MWT-0, MWE-0 Description of Occurrence: Testing of fire protection deluge system for station startup transformers had been in progress. Electrical switching required for this includes pulling potential (PT) fuses. During switching, an incorrect PT compartment was entered and PT fuses for 13.8 KV "B" Bus were pulled, resulting

's ih all load. breakers on "B" bus opening. "Y-2" Essential Instrument Bus was being fed from its alternate source supplied by "B" Bus and loss of "Y-2" removed Channel 2 of the SFAS from service. While performing restoration procedure for SFAS, the operator incorrectly entered SFAS Channel 4 and de-energized this channel in accordance with procedure, satisfying a two out of four actuation logic of the SFAS.* SFAS actuation isolated the Decay Heat System from the Reactor

. Coolant System in violation of Technical Specification 3.4.1.

During this same occurrence, Nuclear Instrument (NI) I was out for servicing.

Because of the loss of Y-2, NI 2 was also lost in violation of Technical Speci-fication 3.9.2.

Designation of Apparent Cause of Failure: Operator error was involved in incor-rectly opening and pulling 13.8 KV "3" Bus PT fuses resulting in loss of one channel of the SFAS. Operator error was also involved in incorrectly commencing energization procedure on operable SFAS channel.

Analysis of Occurrence: Three out of four essential power supplies remained operable. SFAS actuated correctly. There was no decay heat load in the reactor and the decay flow was re-established. Nuclear Instrumentation was returned to service with no change in reactivity within this period. As a result, there was no threat to the health and safety of the public or to station personnel.

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! DAVIS-BESSE UNIT ONE NUCLEAR POWER STATION i SUPPLEMENTAL INFORMATICN FOR LER NP-33-77-7 PAGE 2 Corrective Action: Operator blocked the SFAS actuated components, and returned plant to normal status. Decay lleat Pump re-established RCS recirculation and NI 2 was returned to service. In addition, T&C has installed individual cabi-net door locks with color coded keys for each channel to further ensure against operations in the wrong channel cabinet. Nameplates have been made and installed ,

to prevent pulling wrong PT fuses.

l Failure Data: The SFAS had been actuated once before (LER NP-33-77-6) but the .

cause of the occurrence was not identical.

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