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 Ligdlfeg f11on of Unusual Eventyrgncy Cl XWBtl Commonwealth Edison Co.
nc Zicn 1 Al-PUBUC DOCUMEg[ert _tPMeaEmergency Zion, Illinois 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
- 21. and Unit 2 is in a refueling outage that began in September 1996.
l 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 lE.3N PDR I&E PNO-III-97-024 PDR Ol\\
L' PNO-III-97-024 i a
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
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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 l
March 13, 1997.
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Contact:
DAVID HILLS MARC DAPAS i
(630)829-9733 (630)829-9628 I
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