ML20058K686

AO 263/74-23:on 740826,during Routine Monthly Surveillance of Rcic,Outboard Steam Isolation Valve Failed to Close Completely When Given Close Signal.Valve Reopened & Given Another Close Signal.Valve Closed Properly

ML20058K686
Person / Time
Site:	Monticello
Issue date:	09/05/1974
From:	Mayer L NORTHERN STATES POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
AO-263-74-23, NUDOCS 9102130470
Download: ML20058K686 (2)

Text

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e-NSID NORTHERN S T A T e. S POWER COMPANY win N E A cou s. w e N N E 9 0TA 5 S4 01 50-2.0 Mr. J F O' Leary ,

Directorate of Licensing , c a." _.

Office of Regulation U S Atomic Energy Commission Washington, DC 20545 ABNORMAL OCCURRENCE FIPORT TO THE AEC Malfunction of RCIC Outboard Isolation Valve, MO-2076 1 Report Number: A0 263/74-23 2a. Report Date: September 5, 1974 2b. Occurrence Date: August 26, 1974

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

Monticello, Minnesota 55362

4. Identification of Occurrence:

This report concerns the failure of Reactor Core Isolation Cooling (RCIC) outboard isolation valve, MO-2076, to close completely during routine surveillance.

5. Conditions Prior to Occurrence:

Steady State Power - The plant was at S67. of rated power at the time of the occurrence.

6. Descrintion of occurrence:

On August 26, 1974, during routine monthly surveillance of the Reactor Core Isolation Cooling System (RCIC), the outboard steam isolation valve failed to close completely when given a close signal. The valve was subsequently re-opened and given another close signal. The valve then closed properly.

It was cycled five more times, each time demonstrating proper operation.

7. Designation of Apparent Cause of Occurrence:

Procedure - Ihis valve is normally backseated to prevent steam leakage by the sm upper seat. It is postulated that prior to this occurrence the valve was overly backseated, causing it to trip on over-torque during the first attempt to close. The overly-backseated condition probably resulted ,

from backseating the valve more than once between operations. '

Following the occurrence, the valve was backseated and cycled four times to try to repeat the failure. Each time the valve N

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operated properly. While the plant was in a shutdown condition, the valve was observed to operate smoothly and the torque switch setting was verified to be proper. ,

Inspection of the motor contactor disclosed no abnormality.  ;

8. Analysis of Occurrence:

This occurrence had no effect on the public health and safety. The redundant isolation valve was operable.

9. Corrective Action:

Increased valve operability surveillan.e was initiated following the occurrence. In the future, valves will be cycled immediately prior to backseating, thereby eliminating the possibility of excessive forces created by further application of torque en a previously backseated valve. It is felt that these actions will minimize the probability of similar future occurrences.

10. Failure Data:

There have been no previous similar failures of this or similar conponents.

MO-2076, RCIC Outboard Isolation Valve Motor Operator Serial No. 89749A LLaitorque Motor Operator, Model SMB-000 Philadelphia Gear Corporation MO-2076, RCIC Outboard Isolation Valve 3" - 600# Gate Valve Anchor Valve Company O.

L ti Mayer, PE w

DirectorofNuclear[SupportServices LOM/kn ec: J G Keppler G Charnoff Minnesota Pollution Control Agency Attn. E A Pryzina f

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