PNO-III-93-052, on 930914,reactor Scram & Concurrent Loss of Offsite Power Occurred Caused by Failure of Station Auxiliary Transformer.Power Was Supplied & Two of Three Emergency Diesels Restored to Standby Condition

PNO-III-93-052:on 930914,reactor Scram & Concurrent Loss of Offsite Power Occurred Caused by Failure of Station Auxiliary Transformer.Power Was Supplied & Two of Three Emergency Diesels Restored to Standby Condition

ML20149D573
Person / Time
Site:	LaSalle
Issue date:	09/14/1993
From:	Beverly Clayton, Hague D NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
References
PNO-III-93-052, PNO-III-93-52, NUDOCS 9309210083
Download: ML20149D573 (2)

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, Date: September 14, 1993 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE PN39352 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or 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: Licensee Emeroency Classification Commonwealth Edison Co. General Emergency LaSalle 1 Site Area Emergency ,

Marseilles, Illinois X Alert i Unusual Event N/A

Subject:

LASALLE UNIT 1 LOSS OF 0FFSITE POWER AND REACTOR SCRAM At 11:47 a.m. (CST), September 14, 1993, a reactor scram and concurrent loss i of offsite power occurred at the Commonwealth Edison LaSalle County Station -

Unit 1. The Loss of Offsite Power was caused by the failure of the Unit 1 Station Auxiliary Transformer. A preliminary cause for the failure of the Station Auxiliary Transformer has been identified as the electrical failure of a current transformer (a monitoring device on the Station Auxiliary Transformer). All safety related equipment functioned as designed; all three emergency diesels related to Unit I started and loaded as required. Unit I reactor vessel level and pressure were controlled by the High Pressure Core Spray and Reactor Core Isolation Cooling systems. Unit 2 is in a refueling outage and was not impacted by the event.

To provide additional technical support for the Shift Engineer in the control room, the licensee elected to staff the Technical Support Center onsite, and to partially staff the Corporate Emergency Off site Facility. At 12:19 p.m., )

based on staffing these facilities, the licensec declared an Alert in '

accordance with the General Stations Emergency Plan.

At 1:05 p.m., power was supplied to Unit 1 from Unit 2 and two of the three emergency diesels were restored to the standby condition. The remaining diesel, which supplies the High Pressure Core Spray system, continued to operate. The licensee is cooling the plant down to cold shutdown conditions and the alert will remain in effect until cold shutdown conditions are achieved. Work is in progress to supply Unit I with offsite power through an alternate electrical line-up; the amount of time needed to complete this effort is not known. There has been no discussion of plant restart.

The NRC resident inspector was in the control room at the time when the alert was declared and monitored operator actions. The resident inspector from Oresden Station was sent to LaSalle to provide additional monitoring. Region III staffed the Incident Response Center on declaration of the Alert and formally entered the Monitoring mode at 1:05 p.m. The Monitoring mode was terminated at 2:48 p.m.; however some Region III staff remain in the Incident Response Center to follow the licensee's progress.

The licensee has issued a press release. The State of Illinois has been notified. The information in this preliminary notification has been reviewed with licensee management.

9309210083 930914 PDR I&E-0' M)V {

PND-III-93-052 pyg ..

Date: September 14, 1993 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE PN39352

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. Region 111 (Chicago) was notified of this event by the resident inspector at j the time the alert was declared (12:19 p.m.) This information is current as of 3:30 p.m. on September 14, 1993.

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• Brent Clayton 708-790-5546 708-790-5574 DISTRIBUTION:

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