PNO-V-86-053, on 860805,Unit 2 Turbine Tripped.On 860806,loss of Startup Transformer X03 Caused Loss of Offsite Power Train to Both Units & Resulted in Reactor Trip.Caused by Leak in Main Feed Vent Valve V249

PNO-V-86-053:on 860805,Unit 2 Turbine Tripped.On 860806,loss of Startup Transformer X03 Caused Loss of Offsite Power Train to Both Units & Resulted in Reactor Trip.Caused by Leak in Main Feed Vent Valve V249

ML20205C152
Person / Time
Site:	Palo Verde
Issue date:	08/06/1986
From:	Miller L, Zimmerman R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
To:
References
PNO-V-86-053, PNO-V-86-53, NUDOCS 8608120263
Download: ML20205C152 (2)

J fY PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-V-86-53 Date: 08/06/86 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information presented is as initially received without verification or evaluation and is basically all that is known by Region V staff on this date.

FACILITY: Arizona Nuclear Power Project ' Emergency Classification Palo Verde Units 1/2 XX Notification of Unusual Event DOCKET NO. 50-528/50-529 Alert Site Area Emergency General Emergency Not Applicable

SUBJECT:

REACTOR TRIP IN PALO VERDE UNITS 1 AND 2 On August 5, 1986, at 11:44 pm, MST, the Unit 2 turbine tripped from 50% power. The plant reduced power to 6% while attempting to determine the cause of the turbine trip. On August 6, 1986, at 4:12 am, the loss of Startup Transformer X03 caused a loss of one train of offsite power to Units 1 and 2, and resulted in a reactor trip at each unit. At the time of the trip, Unit I was at 100% and Unit 2 was at 6% power. The affected transformer was aligned in its normal configuration, feeding the Unit 1 "A" train Class lE and non-Class lE busas and Unit 2 "B" train Class lE and non-Class lE buses. When the transformer was lost, the resulting loss of one train of non-class power tripped two reactor coolant pumps in each unit, and both units tripped on anticipated low DNBR. All safety systems appeared to function normally during the trip. A containment purge isolation, fuel building essential ventilation, and a control room essential venti /lation filtration actuation occurred at Unit 2, and is believed to have resulted from a spurious signal from the radiation monitoring system after the partial loss of power.

Basad on the degraded electrical condition at Unit 1 the Shift Supervisor declared. a Notification of Unusual Event at 4:14 AM. Power was restored to the electrical buses from alternate transformers, and the Unusual Event was terminated at 4:59 AM.

The licensee's preliminary investigative efforts indicate that following the Unit 2 turbine trip, a main feed vent valve (V249) leak was generated in the Turbine Building. The 1,eak dripped into an electrical conduit and altimately leaked into an energized 13.8 KV load center (LO2). The load center was damaged following the water intrusion, and the ensuing electrical pertubation resulted in the electrical protection system isolating Startup Transformer X03. The licensee's investigation is ongoing.

The licensee has issued a press release.

8608120263 860806 PDR I&E PNO-V-86-053 PDR O TE3t/

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, s i PNO-RV-86-53 .

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Palo. Verde Units 1/2/3 08/06/86 -

The resident inspectors are continuing to follow the licensee's post trip -

review efforts.

This information is current as of 9:30 AM (MST). August 6,1986.

CONTACT: R. Zimmerman, Sr. Resident Inspector L. Miller (602) 386-5760 (415) 943-3869 i.

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, DISTRIBUTION H St. MNBB Phillips E/W Willste' Air Rights Mail: l Chairman Zech EDO NRR. IE NMSS ADM:DMB l PA OIA RES -DOT:Trans Only Comm. Bernthal MPA AEOD Comm. Roberts ELD

Comm. Asselstine Regions

SECY INPO NSAC ACRS Licensee:

CA (Reactor Licensees) REGION V: FORM.211 PDR Resident Inspector ___ (Revised 3/14/83) l

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