PNO-III-89-040, on 890624,power Lost to All Control Room Annunciators for Reactor & safety-related Sys.Caused by Troubleshooting Ground on Electrical Bus for balance-of-plant Annunciators & Blow Fuses

PNO-III-89-040:on 890624,power Lost to All Control Room Annunciators for Reactor & safety-related Sys.Caused by Troubleshooting Ground on Electrical Bus for balance-of-plant Annunciators & Blow Fuses

ML20245J061
Person / Time
Site:	Zion File:ZionSolutions icon.png
Issue date:	06/26/1989
From:	Lerch R, Shafer W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
References
PNO-III-89-040, PNO-III-89-40, NUDOCS 8906300171
Download: ML20245J061 (1)

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DC d L PRELIMINARY fl0TIFICATION OF EVENT OR UNUSUAL OCCURRENCE PN0-III-89-40 Date 06/26/89 I

'This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or i public^ interest significance. The information is as initially received without verification or evaluation, and is basically all that is known by the Region III staff on this date.

, Facility: Commonwealth Edison Company Licensee Emergency l Zion Unit 2 Classification:

j Post Office Box 767 Unusual Event 7, Chicago, IL 60690 X Alert y Site Area Emergency General Emergency Not Applicable l

Subject:

LOSS OF ALL CONTROL ROOM ANNUNCIATORS l At 3:15 p.m. (CDT) on June 24, 1989, power was lost to all Unit 2 control room annunciators (visual and audible alarms) for the reactor and safety-related systems. Unit 2 was at 99%

power and remained stable throughout the event. Unit I was at 98% power and was not affected.

All other Unit 2 control room instrumentation was functioning properly.

The power loss occurred while the licensee was trouble shooting a ground on the electrical bus for the balance-of-plant (non-safety-related) annunciators. It is thought that a ground may have caused the nomal power supply breaker to trip due to a weak spring.

Licensee personnel then switched power for the control room annunciators from the normal

. power supply to the emergency power supply. With the power supply change, all power supply fuses for the annunciators blew.

The licensee declared an Alert under.its emergency plan.

The fuses were replaced and power for the annunciators was restored using the normal power supply. The licensee determined the fuses blew because of a incorrect wire connection in the emergency power supply circuitry. The wiring error was coreccted and power was restored from the emergency supply. The normal power supply is considered available, however, the licensee is pursuing replacement of the breaker.

Following restoration of power to the annunciators, the alert classification was t:rminated at 3:50 p.m.

The State of Illinois was notified of the alert classification and will be provided with updated information.

The Region III (Chicago) Regional Administrator and other personnel monitored the event by telephone until the annunciators were restored, and the resident inspector subsequently reviewed the licensee's response.

The Headquarters Operation Center was notified of this event at 3:54 p.m. (CDT) on This information is current s of 9:00 a.m. on June 26, 1989.

June 24,19p9lldeur b)P CONTACT:g/ R. M. Lerch W. D. Sh fer DISTRIBUTION:

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