ML20086E410

Ro:On 741126,RHR Svc Water Pump C (P-8-1C) 1,200-amp Circuit Breaker Encountered Significant Damage During Attempted Start.Caused by Migrating Ionized Gases Causing Front Primary Disconnect Device Failure.Breaker Replaced

ML20086E410
Person / Time
Site:	Vermont Yankee
Issue date:	01/09/1975
From:	Riley B VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
NUDOCS 8312070097
Download: ML20086E410 (2)

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VER 10NT YANKEE NUCLEAR POWER CORPORATTON

• SEVENTY SEVEN OROVC STRECT RUTI,AND, VERMONT ' 03701 VYV-3503 'y,.

VERNON. VERMONT 05354 January 9, 1975 G.,.:. ~ '! ( =, h, s Director Directorate of Regulatory Operations, Region I 2 Nh #.,

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United States Atomic Energy Commission 8,79., ,

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631 Park Avenue King ot Prussia Pennsylvania 19406 { y..'

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Operating License DPR-28 '% -,~}' /,

REFERE!'CE: (?

Docket No. 50-271

Dear Sir:

This letter is to inform you of an incident'that occerred at Vermont Yankee during the recently completed cukcli:.g cc::ag .

At 1340 on Novenber 26, 1974, the 1200 amp circuit breaker to the

'C' RHR Service Water Pu=p (P-8-lC) encountered significant damage when the control room operator attempted to start the pump from the control room. ,

The plant was in a cold shutdown condition at the time and the pump was being started as part of a post-maintenance checkout.

An investigation by plant personnel was made and the following conclusions were drawn: .

1. During the refueling outage routine preventative maintenance was performed on the RHR Service' Water Pump that required the use of a Ground and Test device to ground.the Icads to the motor. This device has three bushings which are inserted The into the stationary contact tubes of the breaker compartment.

same Ground and Test device is used for both 1200 and 2000 amp breaker compartments with the only difference in application being that when it is used in_2000 amp compartnents, adapters are put on to the bushings. The 1200 amp contact tubes are ~

11/2" insidc. ' diameter and the 2000 amp adapters are 2" outside i diameter. Prior to using the Ground and Test device in the RHR Service Water Pump breaker compartment, it was used in a 2000 l '

amp breaker compartment and'the adapters were. inadvertently left on the bushings when it was used in the 1200 amp breaker compartment. The adapters spread and: distorted the stationary 8

contact tubes in the R!!R Service Water Pump breaker compartment..

8312070097 750109 6 ILo,5-PDR ADOCK 05000271 f;a -

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'. COPY SErn' REGION 1

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l Ns (~.j ) 0 3 VERMONT YANKEC NUCLEAR POWER CORPORATION h'

Directorate of Regulatory Operations l January 7, 1975 l Page 2

2. The spreading of the stationary contact tubes resulted in an inadequate contact between the tubes and the breaker bushing contacts, When the breaker was closed to start the motor, power arcing took place in the rear primary disconnect device involving all three phases to ground. Ionized gases generated by this arcing migrated and caused the front primary disconnect device to fail in the same manner.

The damaged breaker was returned to the vendor, General Electric Co.,

for inspection and they concurred with the conclusions made by Vermont Yankee.

The entire Bus 4 was inspected for dauage, the RHR Service Water Pump breaker compartment was repaired, and the breaker was replaced prior to the plant startup following the refueling outage.

The Plant Operations Review Committee met to review this incident and made the following recommendations in an attempt to prevent it from a

sveurr n ,:

1. Stencil the Ground and Test device with a warning to remove '

the 2000 amp adapters.before using it in r 1200 amp breaker

, compartment.

2. Stencil the 2000 amp breaker compartments with a warning to ensure that the 2000 amp adapters are installed on the Ground and Test device prior to use in the 2000 amp breaker compartments.

3. Store the 2000 amp adapters in a lock'ed compartment with key control provided by the Maintenance Supervisor or his designated alternate.

- Very truly yours, i

b.

Bradford W. Riley N Plant Superintendent WPM /kbd i

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