ML20011D561

LER 89-015-00:on 891118,reactor Tripped Due to Turbine Trip. Caused by Voltage Transient in Power Circuit to Digital electro-hydraulic Control Sys & Inverter Failure.Inverter Repaired & Returned to svc.W/891218 Ltr

ML20011D561
Person / Time
Site:	Farley
Issue date:	12/18/1989
From:	Hairston W, Dennis Morey ALABAMA POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-015, LER-89-15, NUDOCS 8912280001
Download: ML20011D561 (4)

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. Alabama Power Company

. 40 inverness Center Parkway

.< , Post Ofhce Box 1295 BirminDham. Alabama 35201 Telephone 205 868-5581 W. G. Hairston, ill Senior Vice President Nuclear Operatons AlabamaPower the southern doctic system 10CFR50.73 December 18, 1989 Docket No. 50-364 I

U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Vashington, D.C. 20555 Dear Sir Joseph M. .Farley Nuclear Plant - Unit 2

Licensee Event Report No. LER 89-015-00 Joseph M. Farley Nuclear Plant, Unit 2 Licensee Event Report No. LER 89-015-00 is being submitted in accordance with 10CFR50.73.

If you have any questions, please advise.

Respectfully submitted,

/

V. G. Hairston, III VGH,III/JARimd 8.61 Enclosure cci Mr. S. D. Ebneter Mr. G. F. Maxwell 4 e e o

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Joseph H. Farley - Unit 2 o;$,o,o;o; 3,6,4 i jopl q 3 Reactor Trip Caused By A Voltage Transient On The Digital Electro-hydraulic Control (DEHC) Inverter IV00ff DATI (S) Lf R NuesttR (St REPORT DATI (7) OTHt h F ACH.tfit$ INVOLVlp 401 MONTH DAY TEAR YtAR * * $",l, ,"*[,,7,

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At 0433 on 11-18-89, with the unit operating at 100% power, the reactor tripped i due to a turbine trip. The turbine trip is attributed to a voltage transient in l-the power circuit to the DEHC system. A voltage transient in this circuit is l

l suspected to have caused the DEHC system to erroneously sense a loss of DC power.

The voltage transient is attributed to the failure of the DEHC inverter.

The unit returned to power operation at 0455 on 11-19-89 using the alternate power supply.

The inverter was repaired and returned to service.

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Op 0 l 2 OFi 0l3 Plant and System Identification i

Westinghouse - Pressurized Vater Reactor Energy Industry Identification System codes are identified in the text as [XX].

Summary of Event At 0433 on 11-18-89, with the. unit operating at 100% power, the reactor [AB]

tripped due to a turbine [TA) trip. The turbine trip is attributed to a voltage transient in the power circuit to the digital electro-hydraulic control (DEHC) [JJ) system. A voltage transient in this circuit is suspected to have caused the DEHC system to erroneously sense a loss of DC power. The voltage transient is attributed to the failure of the DEHC inverter.

Description of Event At 0433 on 11-18-89, the reactor tripped due to a turbine trip. The indication was that the DEHC system had experienced a loss of DC input power.

Following the trip, the operators implemented FNP-2-EEP-0 (Reactor Trip or Safety Injection) and FNP-2-ESP-0.1 (Reactor Trip Response), ensuring that the unit was '

safely in Mode 3 (Hot Standby). The unit was maintained in a normal stable condition.

The components that supply power to the DEHC system were inspected after the trip.

The investigation has shown that, at the time of the turbine trip, a voltage -

l transient in the inverter caused the DEHC system to erroneously sense a loss of all L

DC input power. The DEHC system is designed to trip the turbine when both DC power sources are lost. The voltage transient is attributed to internal shorting within the inverter. Several days earlier, the DEHC inverter (located in the Turbine Building) had suffered water intrusion damage from an overhead water leak. The inverter was repaired and returned to service. It appears that some moisture may have remained in the inverter and subsequently caused the inverter voltage transient.

Cause of Event >

1

. The reactor trip occurred due to a turbine trip. A voltage transient occurred in the inverter which supplies power to the DEHC system. The inverter transient is attributed to damage caused by residual moisture from an earlier event.

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Reportability Analysis and Safety Assessment The event is reportable because of the actuation of the reactor protection system. '

After the trip, the following safety systems operated as designed:

main feedvater was isolated with flow control valves and bypass valves closed i auxiliary feedvater pumps started automatically and provided flov to the steam generators source range nuclear instrumentation automatically energized j pressurizer heateis and spray valves operated automatically as required to "

maintain system pressure.

l There was no effect on the health and safety of the public.

Corrective Action The inverter was repaired and returned to service. A shield has been installed to protect the DEHC inverter from vater intrusion.

Additional Information The unit returned to power operation at 0455 on 11-19-89.

L No similar LERs have been submitted by Farley Nuclear Plant.

The inverter was supplied by HDR Power Systems.

.The model number of the inverter is STI-240-010-3, STS-010-3, MBS-010-3.

This event vould not have been more severe if it had occurred under different ,

cperating conditions. +

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