PNO-IV-96-062, on 961122,unit 1 Tripped Due to Electrical Fault in Fuse Box Located Between Unit Auxiliary Transformer & Associated Grounding Transformer.Fault Created Fire in Fuse Box.Fire Extinguished.Root Cause Under Investigation
| ML16342D484 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 11/26/1996 |
| From: | Boynton S, Huey R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | |
| References | |
| PNO-IV-96-062, PNO-IV-96-62, NUDOCS 9611270075 | |
| Download: ML16342D484 (2) | |
November 26, 1996 PRELIMINARYNOTIFICATIONOF EVENT OR UNUSUAL OCCURRENCE PNO-IV-96-062 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 Region IV staff in Arlington, Texas on this date.
~Facitit Pacific Gas 5 Electric Co.
Diablo Canyon 1
Avila Beach, California Dockets: 50-275 Licensee Emer enc Classification Notification of Unusual Event Alert Site Area Emergency General Emergency X Not Appiicable
Subject:
PLANT SHUTDOWN GREATER THAN 72 HOURS On November 22, 1996, at 11:47 a.m. (PST), Diablo Canyon Power Plant, Unit 1, tripped due to an electrical fault in a fuse box located between the unit Auxiliary Transformer (Aux) 1-1 and its associated grounding transformer.
The fault created an electrical fire within the fuse box, which caused localized damage to the box and to the buswork between Aux 1-1 and its associated 12 kV busses.
The fault resulted in a generator trip and subsequent reactor trip. In addition, the ability to backfeed power to the unit from the 500 kV offsite power source was lost.
The fire was extinguished when Aux 1-1 was isolated from the 12 kV busses during the bus transfer to startup power.
The major loads on the 12 kV busses include the reactor coolant pumps and the unit circulating water pumps (CWPs).
Operator response to the transient was good, including response to two equipment problems which complicated the transient.
First, CWP 1-2 was selected but failed to automatically restart following the transfer of its respective bus to startup power.
This led to a loss of all circulating water to the main condenser.
Operators closed the main steam isolation valves and removed decay heat via the steam generator atmospheric dump valves.
No interaction between the atmospheric dump valves and the main steam safety valves was noted, which had occured on some previous events.
- Second, one of the two intermediate range nuclear instruments failed to properly track the decay of reactor power.
This required. operators to manually reenergize the source range instruments.
Unit 1 is currently in Mode 3, with the 500 kV backup power source restored, pending the results of the licensee's investigation of the cause of the fire and determination of required corrective actions.
The licensee is investigating the root cause of the electrical fault and evaluating any potential damage to other electrical equipment.
The licensee does not expect to restart the unit before Wednesday, November 27.
The state of California was informed.
Region IV received notification of this occurrence by phone from the resident inspectors at 12:10 p.m. (PST) on November 22.
Region IV has informed EDO, NRR, and PA.
Contact:
R. HUEY (51 0)975-0342
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rl This information herein has been discussed with the licensee and is current as of 1 p.m.
November 25, 1996.
96i i270075 96i i26 PDR ISE PNQ-KV-96-062 PDR S. BOYNTON (805) 595-2353
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