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Final ASP Analysis - Farley 2 (LER 364-85-010)
	ML20149K332
Person / Time
Site:	Farley
Issue date:	05/28/2020
From:	Christopher Hunter; NRC/RES/DRA/PRB
To:	;
	Littlejohn J (301) 415-0428
References
	LER 1985-010-00
	Download: ML20149K332 (5)
	v • d • e

PRECURSOR DESCRIPTION AND ANALYSIS LER No.:

364/85-010 Event

Description:

Loss of Power to 4160-V Nonsafety Buses Date of Event:

July 15, 1985 Plant:

Farley 2 EVENT DESCRIPTION Sequence With severe thunderstorms in the area, a reactor trip occurred because of a high negative flux rate detected by the power range nuclear detec-tors.

Lightning apparently caused a voltage surge that tripped both the normal and redundant power supplies in rod control system power cabinets 2AC and 2BD.

The control rods powered by these cabinets dropped into the core, causing the high negative flux rate.

Shortly after the trip (15 s and 18 s), both generator output breakers opened prematurely, resulting in deenergizing all three RCPs before the fast dead bus transfer feature could transfer their power supply from the auxiliary to the startup transformers.

The breaker delay should have been 30 s.

The deenergized buses were 4160-V buses 2A, 2B, and 2C.

Bus 2A powered RCP 2A, circulating water pump 2A, and condensate pump 2B.

Bus 2B powered RCP 2B and circulating water pump 2B.

Bus 2C powered RCP 2C.

Corrective Action Testing was conducted to determine the cause of the premature opening of the generator output breakers, but the cause could not be determined.

Reactor and turbine trip signals were introduced into the generator out-put breaker control circuitry, and the breakers were found to operate properly.

No electrical or mechanical problem that would have caused the output breakers to open prematurely could be found.

The automatic fast dead bus transfer feature of 4160-V buses 2A, 2B, and 2C was also tested and found to operate properly.

Plant/Event Data Systems Involved:

Control rod power, RCPs, and 4610-V breakers and buses Components and Failure Modes Involved:

Control rod system power cabinets -

power failure from lightning swings All three RCPs, two circulating water pumps, and one condensate pump -

tripped off Fast dead bus transfer -

failed because of premature opening of the generator output breakers Event Identifier:

364/85-010 E-2 22

Component Unavailability Duration:

NA Plant Operating Mode:

1 (99% power)

Discovery Method:

Operational event Reactor Age:

4.7 years Plant Type:

PWR Comments Plant trip from loss of RCPs MODELING CONSIDERATIONS AND DECISIONS Initiators Modeled and Initiator Nonrecovery Estimate Transient 1.0 Nonrecoverable Branches Impacted and Branch Nonrecovery Estimate MFW 0.34 Not recoverable from control room but possible recovery locally at equipment Secondary-side 0.12 only one condensate pump was powered depressurization by affected buses, and recovery of one or both seemed likely Plant Models Utilized PWR plant Class B Event Identifier:

364/85-010 E-223

CONDITIONAL CORE DAMAGE CALCULATIONS LER Number; Event

Description:

Event Date:

Plant:

364/85-010 Loss of Power to 4160V Non-Safety Buses 7/15185 Farley 2 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES TRANS SEQUENCE CONDITIONAL PROBABILITY SUMS End State/Initiator CV TRANS Total

1.

OOOE+00 Probability

9.

373E-06

9.

373E-06 CD TRANS Total 4.7 11E-06

4.

71 IE-06 ATWS TRANS Total DOMINANT SEQUENCES End State: CV Conditional Probability:

109 TRANS -RT -AFN -PORV.OR.SRV.CHALL SS.RELEAS.TERM HPI End State: CD Conditional Probability:

126 TRANS -RT AFW MFW HPI(F/B) -SS.DEPRESS COND/MFW End State: ATWS Conditional Probability:

128 TRANS RT

3.

OOOE-05

3.

OOOE-05

3.

817E-06

1.

141E-06

3.

OOOE-05 Event Identifier:

364/85-010 E-224

SEQUENCE CONDITIONAL PROBABILI TIES Sequence End State Seq. Prob Non-Recovif 101 TRANS -RT -AFW PORV.OR.SRV.CHALL -PORV.OR.SRV.RESEAI SS.RELE AS.TERM HPI 102 TRANS -RT -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HP R/-HPI -SS.DEPRESS -LPR/-HPI.HPR 103 TRANS -RI -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HP R/-HPI -SS.DEPRESS LPR/-HPI.HPR 104 TRANS -RI -AFW PORV.OR.SRV.CHALL PORV.OR.SRV.RESEAT -HPI HP RI-HPI SS.DEPRESS 109 TRANS -RI -AFW -PORV.OR.SRV.CHALL SS.RELEAS.TERN HPI 119 TRANS -RI AFW MFW -HPI (F/B) -HPR/-HPI PORV.OPEN -SS.DEPRESS

-COND/MFW 120 TRANS -RI AFW MFW -HPI(FIB) -HPR/-HPI PDRV.OPEN -SS.DEPRESS COND/MFW 121 TRANS -RI AFW MFW -HPI(F/8) -HPR/-HPI PORV.OPEN SS.DEPRESS 122 TRANS -RI AFW MFW -HPI(FIB) HPR/-HPI -SS.DEPRESS -COND/MFW 123 TRANS -RI AFW IIFW -HPI(FIB) HPR/-HPI -SS.DEPRESS COND/MFW 124 TRANS -RI AFW MFW -HPI(FIB) HPR/-HPI SS.DEPRESS 125 TRANS -RI AFN MFW HPI(F/B) -SS.DEPRESS -COND/MFW 126 TRANS -RI AFW MFW HPI(F/B1 -SS.DEPRESS COND/MFW 127 TRANS -RI AFN MFW HPI(F/B) SS.DEPRESS 128 TRANS RI CV CV CD CD CV Cv CD