PNO-III-89-016A, on 890306,Unit 1 Returned to Operation Following Reactor Scram on 890302.Unit 2 Remained in Operation & Unit 2 Station Auxiliary Transformer,Which Failed on 890302,repaired & Returned to Svc

PNO-III-89-016A:on 890306,Unit 1 Returned to Operation Following Reactor Scram on 890302.Unit 2 Remained in Operation & Unit 2 Station Auxiliary Transformer,Which Failed on 890302,repaired & Returned to Svc

ML20235Y706
Person / Time
Site:	LaSalle
Issue date:	03/06/1989
From:	Forney W, Harrison J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
References
PNO-III-89-016A, PNO-III-89-16A, NUDOCS 8903140511
Download: ML20235Y706 (1)

kINARYNOTIFICATIONOFEVENTORU SUAL 0 CURRENCE PHO II-89-16A M e March 6, 1989 k 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 djd known'by the Region III staff on this date.

t Facility: Commonwealth Edison Co. Licensee Emergency LaSalle Units 1 & 2 Classification:

Marsellies, IL 61341 X Unusual Event Alert Docket No. 50-373; Site Area Emergency 50-374 General Emergency Not Applicable

Subject:

UNIT 1 REACTOR SCRAM RELATED TO UNIT 2 TRANSFORMER FAULT-----UPDATE

' Unit I returned to operation on March 6, 1989, following the reactor scram which occurred March 2, 1989. Unit 2 had remained in operation and the Unit 2 Station Auxiliary

-Transformer, which failed on March 2, was repaired and returned to service.

i The NRC Augmented Inspection Team (AIT) completed its review of the event at 8 p.m. on March 4, 1989, and on March 5 the Regional Administrator concurred in the licensee's decision to restart the reactor.

The initiating event was determined to be the loss of the Unit 2 Station Auxiliary Transformer as a result of the failure of a lightning arrester. The arrester failure was

'not weather-related; the device has been sent off-site for evaluation. A Unit 1 phase differential relay sensed the resulting undervoltage condition and responded more quickly than normal, causing the Unit 1 turbine trip and reactor scram. The quicker response was--

caused by drifting of the relay's set point.

The AIT determined that the low or under voltage conditions during the transfer of power -

sources on both units caused other equipment responses including the loss of the station air compressors, the process computer for both units, actuation of isolation valves on the reactor water cleanup system._ locking up of Unit 2 recirculation flow control valves and the feedwater regulating valve, and the tripping of a Unit-2 reactor protection system alternate power supply breaker. The reported drifting of the set points on Static-0-Ring switches did

.not contribute to the events.

RegionIII(Chicago)issuedaConfirmatoryActionLettertothelicenseedocumentingits agreement to fully evaluate the event and to obtain NRC concurrence before resuming operation of Unit 1.

The State of Illinois will be notified of this updated information.

Thisinformatponiscurrentasof4p.m., March 6,1989.

~ CONTACT: so (FTS388-5635) n 388-5590)

DISTRIBUTION:

WHlTE FLINT NORTH 1 MNBB REGIONS FAX TO:

Chairman Zech CA AEOD RI INP0fgjP --8: 0 (o Comm. Roberts OGC ARM RII Comm. Carr 01 OIA RIV NSAC Licensee 1PrFy _ )F Comm. Rogers ED0 RV NRC Ops Ctr #:Id Comm. Curtiss NRR NL MAIL T0: PDR(8/634-3343)plb SECY' NMSS RES DCS (Orig.)

'GPA/SLITP/PA' ACRS D0T (Trans. Only) pg e403140511 s90366

$ -II 89-16A N GM