PNO-III-97-024, on 970311,Unit 1 Sys Auxiliary Transformer Tripped as Result of Actuation of Sudden Pressure Relay, Indicating Possible Fault in Transformer.Nrc Providing round-the-clock Insp Coverage at Zion

PNO-III-97-024:on 970311,Unit 1 Sys Auxiliary Transformer Tripped as Result of Actuation of Sudden Pressure Relay, Indicating Possible Fault in Transformer.Nrc Providing round-the-clock Insp Coverage at Zion

ML20138F798
Person / Time
Site:	Zion File:ZionSolutions icon.png
Issue date:	03/14/1997
From:	Dapas M, Dave Hills NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
References
PNO-III-97-024, PNO-III-97-24, NUDOCS 9705060051
Download: ML20138F798 (2)

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March 14, 1997 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE PNO-III-97-024 This preliminary notification constitutes EARLY notice of events of l POSSIBLE safety or public interest significance. The information is as initially received without verification or evaluation, and is-basically all that is known by Region III staff (Lisle, Illinois) on this date.

Facility Commonwealth Edison Co. Ligdlfeg XWBtlnc f11on of Unusual Eventyrgncy Cl

! Zicn 1 Al-Zion, Illinois PUBUC DOCUMEg[ert _tPMeaEmergency Dockets: 50-295 General Emergency Not Applicable

Subject:

LOSS OF 0FFSITE POWER On March 11, 1997 at 3:54 p.m. (CST), the Unit 1 system auxiliary transformer (SAT) tripped as a result of actuation of its sudden

pvssure relay, indicating a possible fault in the transformer. The SAT supplies offsite power to the three Unit 1 engineered safety feature (ESF) buses.

When the transformer tripped, both Unit 1 emergency diesel generators 1 (EDGs) and the shared EDG started and successfully supplied power to the Unit 1 ESF buses, Shutdown cooling was lost for 8 minutes due to the 7rruption of power, and the reactor coolant temperature increased ;com 92 to 112 degrees Fahrenheit.

Offsite power has been available to Unit 2 throughout the event and power can be provided to all Unit 1 ESF buses via an electrical crosstie to the Unit 2 SAT if necessary. Unit 1 has been shut down since February l

21. and Unit 2 is in a refueling outage that began in September 1996.

! The licensee declared an Unusual Event as a result of the loss of l offsite power to Unit 1 and activated its Technical Support Center.

l Operators near the transformer at the time of the event observed no fire or explosion, and to date, no visible transformer damage has been i

I 9705060051 970314

! PDR I&E lE.3N PNO-III-97-024 PDR Ol\

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PNO-III-97-024 i identified. I As of 1 p.m. on March 13, the plant remains in an Unusual Event. The i shared EDG has been secured and power to the associated Unit 1 ESF bus  !

l is now being supplied via the electrical crosstie with Unit 2 Power to  !

l the other two Unit 1 ESF buses, which are supplying power to the l Residual Heat Removal pumps, continues to be supplied by the two Unit 1 l EDGs.

l The licensee is conducting an investigation to determine the root cause of the SAT trip. Transformer oil samples have being analyzed and no )

indications of transformer degradation were found. The licensee is investigating the possibility that the trip may have been caused by a  ;

spurious signal.

The NRC is providing round-the-clock inspection coverage at Zion.

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The States of Illinois and Wisconsin will be notified. The information  !

in this preliminary notification has been reviewed with licensee management.

The licensee notified the NRC Operations Center of this event at 4:45 ,

p.m. CST on March 11, 1997. This information is current as of 1 p.m. on -

March 13, 1997.

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Contact:

DAVID HILLS MARC DAPAS i (630)829-9733 (630)829-9628 -

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