PNO-V-91-003, on 910307,unit 1 Shutdown for Refueling Operations & Loss of Offsite Power.Licensee Personnel Manually Moved New Module,Still in Mast,Away from Reactor Vessel & Core

PNO-V-91-003:on 910307,unit 1 Shutdown for Refueling Operations & Loss of Offsite Power.Licensee Personnel Manually Moved New Module,Still in Mast,Away from Reactor Vessel & Core

ML20203C614
Person / Time
Site:	Diablo Canyon
Issue date:	03/07/1991
From:	Morrill P, Narbut P NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
To:
References
PNO-V-91-003-01, PNO-V-91-3-1, NUDOCS 9712150367
Download: ML20203C614 (1)

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&fL ff}kp e r c hg  % fi v 3 M t PRELIM!N_ARY NOT!f! CATION OF EVENT OR UNUSUAL OCCURRENCE-PNO-Y-91-03 Date 03/07/91 y D preliminary notification constitutes EARLY notice of events of POSSIBLE safety or 4 Jc interest significance. The information presented is as initially received

'w;;ut verification or evaluation and is basically all that is known by Region Y staff on this date.

FACILITY: PACITIC GAS & ELECTRIC COMPANY Emergency classification DIABLO CANYON UNIT 1 X Notification of Unusual Event DOCKET NO. 50-275 ~ Alert SAN LUIS OBISPO COUNTY, CA ~ Site Area Emergency General Emergency Not Applicable

SUBJECT:

LOSS OF OFFSITE POWER WHILE REFUELING At approximately 8:10 a.m. PST on March 7, 1991, with Unit I shutdown for refueling operations, a loss of offsite power occurred when a mobile crane near the Unit 1 phase "A" main transformer, caused a short circuit to ground and a trip of the main transformer. The startup bus for Unit I was not supplying offsite power at the time of the event as the bus was deenergized for preventive maintenance. The two Unit 1 and the swing emergency diesel generators started and loaded upon the loss of offsite power. Major safety equipment was reported to actuate. The running residual heat removal (RHR) pump deenergized due to the loss of power but was manually restarted approximately one minute later. There was no observed co e temperature increase from the one minute loss of RHR.

p licensee declared an Unusual Event at 8:30 a.m. PST on March 7, 1991, due to the t  ! loss of Unit 1 offsite pcwer. The Unit was in the process of being refueled.

C/188 of 193 fuel modules currently reinstalled in the core. One new fuel module was in the refueling mast, over the core, when the event occurred. Licensee personnel manually moved the new module, still in the mast, away from the reactor vessel and core. One new fuel module was secured in the upender in the spent fuel pool. Unit 2 expsrienced a 150 MW transient, but was unaffected, and continued to operate normally.

The licensee has notified state and local officials. FEMA headquarters and FEMA Region 9 were also notified. The NRC resident inspectors followed the licensee's efforts from the control room. The licensee has iss~ued a press release.

By 1:00 p.m. PST on March 7, 1991, the licensee had restored power to the startup bus, and the three emergency dicsol generators were secured. The Unusual Event was terminated at 1:25 p.m. PST.

This event is of significant interest due to the similarities to the loss of offsite '

power at Vogtle; however, adequate cooling was available to the core, both RHR pumps wire operable, and onsite AC power was not lost.

g l An Augmented Inspection Team comprised of Region V, ATOD, and7NRR personnel will be I dispatchedtothesiteonMarch8,1991toreviewtheegt. ,.k yD l This information is current as of 4:30 p.m. PST on MarchD,1i91. 1 5 ,(' \

CONTACT: P. Morrill, RV P. Narbut E f' FTS 403-3740 805-595-235/0 3~

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