ML17266A145

Updated LER 79-028/01X-1:on 790903,in Cold Shutdown During Hurricane,Cable Fell Into Startup Transformer B.Ac Electrical Sys B de-energized & Diesel Generator Failed to Start.Caused by Delay in B Diesel Binding

ML17266A145
Person / Time
Site:	Saint Lucie
Issue date:	02/11/1980
From:	James D FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML17207A841	List: ML17207A840 ML17266A145
References
LER-79-028-01X, LER-79-28-1X, NUDOCS 8002220334
Download: ML17266A145 (3)

Text

Initial Report-Se ember 17, 1979 NRC PORI0 260 U S. NUCLEAR REGULATORY COMAtISSIOI+

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50 O9 EV ENT 0 ESCR IPTION ~O PR 0 9 4SLE COaI5 ECU B4CES +Io 0 2 While in the cold shutdown con%Cion during Hurricane David, a cable fell across lines jnto the "B" S/U transformer, causing a lockout on the

~0 East Bus and de-energizing the "B" S/U transformer. The "B" A.C. electri-cal system was de-energized, and the "B" Diesel Generator (.DG) failed to start. Following an electrical check-out, the "B" DG was manually started

'Adequate core cooling was maintained at all times. This is the fifth occurrence of this'type (See LERs 335-76-21, 76-44, 77-3 and 77-]5).

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~YQ ~AQ 41 42 13 40 IQ 44 3 3 4 51'c 47 CAUSE OESCRIPTION ANO CORRM'PIV ACTiONS O2l An investighti on revealed that a rela in the auto-start circuitr of the

~ "B" DG was mechanically binding. This relay was. replaced. An operational test was then satisfactorily completed whereby the "B" S/U transformer (which had been repaired and tested) was intentionally de-energized. The "B" DG was observed to auto-start an 0' 2 9 P*CIU.Y.

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0'AAIA OP PREPARER D- K. James (3051 552-3813

REPORTABLE OCCURRENCE 335-79-.28, Update 81 LICENSEE EVENT REPORT PAGE TWO Additional Event Descri tion and Probable Conseouences 4

While in the cold shutdown condition (Mode 5) during the passage of Hurricane David, a support cable for the tower crane in th ,Unit 2 construction area fell across 'lines 'into the "B" Start-up 'Trans=ormer. A lockout occurred on the East Bus and.the "B" Start-up Tra .sform r was de-energized.

The "B" side of the electrical system de-energized with the exception of the "B" DC Bus which was carried by the "8" battery. The "B" Inverter failed to respond but the "D" Inverter remained in service. A blown fuse was discovered later in the "B" Inverter circuit. Tne "AB" A.C. Busses were lost as they were tied to the "B" side. The "AB" D.C. Bus was lost as it "B" D.C. Bus, which is assumed to have de-energized as a result of the current was tied to transient produced by the event. The SUPS (including instrumentation, annunciation, lighting, communications [except PAX and BELL], NAMAS and Sequence of Events Recorder) was also lost. At this tim i-: was discovered that "B" Diesel Generator was not supplying loads (failed to start). Follovong a visual and electrical check-out of'he "B" Diesel Generator, 'it was manua'}ly started.

Adequate core cooling was maintained and verified >y starting the "A" IPSI pump and manually controlling Shutdown Cooling flow.

Additional Cause D sc. i~t'.on and Corrective'Action The "A" Diesel Generator was yepified OPERABLE. All of the electrjca] busses and components lost during event were re-energiz d. Since the reason fop the "B" Diesel Generator not starting autorqatjc~lly on vndervoltage was not

.known, and the potential for a faulted bus or ground was suspected, a thorough check-out was conducted prior to manually starting and loading the "B" Diesel Generator. Two days following the event, a plant staff review and investigation revealed that the K22 relay in the auto-start circuitry of the "B" was mechanically binding. This relay was replaced. 'Subsequently, Diesel'enerator an operational test was .satisfactorily completed whereby the "8" Start-up Transformer (which was repaired and tested) was intentionally de-ener g'ized, and auto-start and loading of the "B" Diesel Generator was verified to occup,

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