ML20058K792

AO 263/74-20:on 740712,during Attempts to Start RHR Svc Water Pump 11 for Torus Cooling,Motor Breaker Would Not Close.Caused by One Contact of Spring Charging Motor Limit Switch Did Not Close When Closing Spring Fully Charged

ML20058K792
Person / Time
Site:	Monticello
Issue date:	07/22/1974
From:	Mayer L NORTHERN STATES POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
AO-263-74-20, NUDOCS 9102140402
Download: ML20058K792 (2)

Text

Regul&[ Docket File O 2 N]

NORTHERN STATES POWER COMPANY

- % q'N./D, MIN N E A POLI S, MIN N E SOTA 55401

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g n ~!'r rU Nb J.l I Mr. J F O' Leary, Director fN vgLo51974 t-v Directorate of Licensing .y Office of Regulation N

' "m e:N :5 C n c U S Atomic Energy Commission A t m :n / ,f Washington, DC 20545 [" h

.~ w-ABNORMAL OCCURRESCE REPORT TO THE AEC ,

Mal function of No. 11 RHR Service Water Pump Motor Breaker Om

1. Report 1; umber: A0 263/74-20 - . Q; ,

2A. Report Date: July 22, 1974  % ~>

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2B. Occurrence Date: July 12, 1974 'y. ._

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3. Facility: Monticello Fuclear Generating Plant (DPR-22) -

Monticello, Minnesota 55362 4 Identification of Occurrence: W This report concerns a malfunction of the No. 11 Residual Heat Removal (RHR) Service Water pump motor breaker.

5. Conditions Prior to Occurrence:

Steady State Power - The Plant was at 87*/. of rated power at the time of the occurrence.

6. Description of Occurrence:

On July 12, 1974, during attempts to start the No. 11 RHR SW pump for torus cooling, the motor breaker vould not close. The redundant pump in "A" loop and the pumps in the redundant "B" loop were demonstrated to be operable. The breaker was replaced with a spare and the No. 11 RHR SW pump was demonstrated operable,

7. Desienation of Apparent Cause of Occurrence:

Component Failure - Inspection revealed that one contact of a spring charging motor limit switch did not close when the closing spring was fully charged. With this contact ,

open, the closing relay could not be energized and  !

the breaker was prevented frce being closed wither remotely or locally. Further investigation revealed that the limit switch (the third in a stack of three limit switches which comprise the spring charging motor limit switch assembly) contacts would not close due to foreign material in the switch assembly.

9102140402 740722 b[7~1 CF ADDCK 05000263 (Over)

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.Q NORTHERN CTATE"3 POWER COMPANY

8. Analysis of Occurrence:

This occurrence had no effect on the public health and safety. The remaining three operable RHR SW pumps provided more than sufficient cooling capacity.

9. Corrective Action:

The breaker for the No. 11 RHR Service Water pump motor was replaced with a spare breaker. The faulty spring charging motor limit switch assembly was cleaned. The breaker was operated several times and the subject limit switch functioned properly each time. It is noted the Preventive Maintenance (FM) procedure for this breaker specifically calls for inspecting, cleaning and adjusting these and all other auxiliary switches associated with the breaker. The FM procedure for this brecker was performed during the Spring 1974 refueling outage.

The breaker was operated successfully several times since the PM was performed and prior to the occurrence. It is believed that the mal-function of this limit switch is an isolated occurrence and the existing program will minimize the probability of similar future occurrences.

10. Failure Data:

There have been no previous similar failures or malfunctions of this or similar co=ponents.

Spring charging motor limit switch GE Model CR 29400301 in Breaker Type:

GE Magna-Blast Circuit Breaker AMH-4,76-250-0D L 0 Mayer, PE '

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Director of Nuclear Support Services LOM/kn ec: J G Keppler G Charnoff Minnesota Pollution Control Agency Attn. E A Pryzina

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