ML20151H020

IE Info Notice 82-01, Auxiliary Feedwater (AFW) Pump Lockout Resulting from Westinghouse W-2 Switch Circuit Mod

ML20151H020
Person / Time
Issue date:	01/22/1982
From:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
To:
References
IEIN-82-01, IEIN-82-1, NUDOCS 8107230043
Download: ML20151H020 (5)

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8107230043 IN 82-01

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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 January 22, 1982 IE INFORMATION NOTICE N0. 82-01: AUXILIARY FEEDWATER PVMP LOCK 0UT RESULTING FROM WESTINGHOUSE W-2 SWITCH CIRCVIT MODIFICATION Description of Circumstances:

On September 14, 1981, Coninonwealth Edison's Zion Unit 2 was conducting a normal plant cooldown to begin a refueling outage. The reactor coolant system was operating at 350 psig and 250'F. Both residual heat removal (RHR) systems were operating to remove decay heat and control reactor coolant system temperature.

Steam generator water levels dropped below the 10% low level auxiliary feedwater (AFW) pump auto-start setpoint, and the motor-driven AFW pumps activated as designed. The operator placed the control switches in the pull-to-lock-out position to stop the AFW pumps. Later, to control the rate of plant cooldown, the operator tried to increase the cooldown rate by feeding water to the steam generators. The AFW pumps would not restart on command. The power supply circuit breaker for one of the pumps was momentarily racked out to the

. ' J3) disconnect position and then racked back in for service. As a result of this

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procedure, the AFW pump restarted. No further problems were encountered during the plant cooldown operation.

Investigation into the problem revealed that the licensee's modification to the Westinghouse W-2 control switch used with the AFW pumps differed fram that recommended in IE Bulletin 80-20 (IEB). IEB 80-20, entitled "Failures of Westinghouse Type W-2 Spring Return to Neutral Control Switches," recommended using only the existing green status light to provide early detection of an open circuit caused by a neutral position (auto-start) contact failure of the control switch. However, in this application, the licensee's modification included both the red and green status lights. This resulted in a sneak

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circuit path which prevented AFW pump restart under certain circumstances.

Following an auto-start of the AFW pump and the subsequent securing of that l

pump by placing the control switch in the pull-to-lock-out position, the licensee found that a live continuous circuit existed between the' red light and the anti-pump coil. This sneak current path prevented deenergization of the anti-pump coil (circuit reset) that is necessary for pump restart.

The licensee reports that, following the initial circuit modification, the f

< sneak path was noted to cause the red indicating light to glow only dimly when the control switch was placed in the pull-to-lock-out or trip positions (see Figures 1 through 3 and Table 1). However, the sneak path was not fully analyzed at that time, and no detailed function testing of the modified circuit l

[c was performed. Note that when the red light is used to indicate "pump on," as in this application, the light should not go on when the control switch has been placed in either the pull-to-lock-out or trip positions.

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..s 82-01 January 22, 1982 Page 2 of 2 h

Circuit modifications may have been made at various plants in response to information in IEB 80-20. These modifications, where different from IEB 80-20 recomendations, may have caused sneak paths with various degrees of impact that may not have been detected by previous engineering analysis or post-installation testing.

This information notice is provided as an early notification of a potentially significant matter. It is expected that recipients will review.the information for applicability to their facilities. No specific. action or response is required at this time. If you have 6ny questions regarding this matter, please contact the Regional Administrator of the appropriate NRC Regional Office.

Attachments:

1. Figures 1, 2 and 3

2. Rec.ently issued IE Information Notices -

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Figure 3 Sneak Path in Control Switch "Neutral" Position with Auto Start Signal Present TABLE 1 Legend for Figures 1-3 CS Control Switch 1 Contacts Y Y Lock Relay Contracts x Latch Release Coil a,b y Lockout Relay Coil '

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