View source for PNO-V-85-029, on 850518 & 20,reactor Trip & Safety Injection Occurred Due to Loss of Vital Instrument Ac Power.Caused by Failure of Transformer in Vital Instrument Ac Inverter IY-13 & IY-12 Output Breaker Tripping Open

{{Adams
| number = ML20128C292
| issue date = 05/20/1985
| title = PNO-V-85-029:on 850518 & 20,reactor Trip & Safety Injection Occurred Due to Loss of Vital Instrument Ac Power.Caused by Failure of Transformer in Vital Instrument Ac Inverter IY-13 & IY-12 Output Breaker Tripping Open
| author name = Dodds R, Mendonca M
| author affiliation = NRC OFFICE OF INSPECTION &amp; ENFORCEMENT (IE REGION V)
| addressee name = 
| addressee affiliation = 
| docket = 05000275
| license number = 
| contact person = 
| document report number = PNO-V-85-029, PNO-V-85-29, NUDOCS 8505280243
| document type = PRELIMINARY NOTIFICATION OF EVENT OR OCCURRENCE (PNO,, TEXT-INSPECTION &amp; AUDIT &amp; I&amp;E CIRCULARS
| page count = 1
}}
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i-PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE-PNO-V-85-29              Date: 05/20/85 (This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public
     -intorest significance. The information presented is as initially received without verification cr evaluation and is basically all'that'is known by Region V staff on this date.
FACILITY: ' Pacific Gas & Electric Company                         Emergency Classification Diablo Canyon Unit 1.                                   XX Notification of Unusual Event Docket No. 50-275                                          Alert San Luis Obispo County, California                         Site Area Emergency General Emergency Not Applicable

==SUBJECT:==
REACTOR TRIP AND SAFETY INJECTION EVENTS
     - At 7:13 am (PDT) on May 18, 1985, and again at 5:20 am (PDT) on May 20, 1985, a reactor trip cnd safety injection occurred due to the loss of vital instrument AC power.
With the reactor plant at 100% power on May 18, 1985, the first event happened at 7:13 am when a transformer in vital instrument'AC inverter IY-13 failed. Subsequent loss of AC panel PY-13        !
resulted'in a reactor trip from false instrument indication of an open reactor coolant pump bruker. Almost immediately thereafter, a safety injection was initiated due to a false high storm line flow coincident with low steam pressure indication. An " Unusual Event" was
     .diciared.- Plant conditions were stabilized in accordance with emergency operation procedures and the event terminated at 8:01 am. All safeguard systems operated appropriately except that
     . Discel Generator 1-3 was manually _ shutdown af ter only 2 to 3 minutes when a belt broke on the cugine driven fuel oil pump. The reactor was started up and returned to power operation
      .following repair and testing of'the failed inverter and-diesel generator at 5:30 am on M:y'19, 1985.
On May-20, 1985, at 5:20 am, another reactor trip and safety injection was experienced from 55% power'when vital instrument inverter IY-12 output breaker tripped open. With AC panel PY-12 de-energized, the reactor tripped once again from a false instrument indication of an opsn reactor coolant pump breaker. Safety injection initiated immediately due to a false high atsrm line flow coincident with low-low "TAVC" indication. Plant conditions were stabilized end all safeguard system operated acceptably. An " Unusual Event" was declared at 5:20 am and~
tsrainated at 5:49 am..
Tha-licensee has included this information in their daily report to the media and, as a rscult,-has been responding to media inquiries. Region V will also respond to inquiries.
CONTACT:   R. T. Dodds                             M. Mendonca FTS'463-3720                             (805) 595-2354 DISTRIBUTION
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          ,    8505280243 850520                                                            ~~~)7 PDR    ISnE                                                                    .
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PNO-V-85-029        PDR-i}}

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