ML20042E185

LER 90-002-00:on 900314,determined That Halon Release in Either ESF Switchgear Room Would Trip Both Class 1E Electrical Equipment Air Conditioning Units.Caused by Lack of Design Criteria.Criteria revised.W/900413 Ltr

ML20042E185
Person / Time
Site:	Wolf Creek
Issue date:	04/13/1990
From:	Bailey J, Mike Williams WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-002, LER-90-2, NO-90-0118, NO-90-118, NUDOCS 9004200354
Download: ML20042E185 (5)

Text

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W$LF CREEK NUCLEAR OPERATING CORPORATION -  ;

~ John A. Beney

' vieo Preensent i 1

Nucteer Opershons  :

l ApM 1 13, 1990 NO 90-0118  ;

U. S.: Nuclear Regulatory Commission i

ATTN: Document Control Desk Hail Station P1-137 -

Washington, D. C. 20555 Subjects Docket No. 50-482:,-Licensee-Event Report 90-002 Gentlemen ,

The attached Licensee Event Report (LER) is submitted-pursuant to 10 CFR -

50.73 (a) (2) (v) as a condition that alone could 'have prevented the fulfillment of a safety function.

Very.'truly yours, L Q. 24 - c John A. Bailey

~Vice President nuclear Operations ,

JAB /jra ,

Attachment cc: R. D. Martin (NRC), w/a D. Persinko (NRC), w/a D. V. Pickett (NRC), w/a M. E. Skow (NRC), w/a l'L 0004200 r,4 soc,4 ; 7 FDF ADOc t. cvfiO O O 4 8

? FDC P.O. Box 411/ Burhngton, KS 66839 / Phone:(316) 3644831 An Equal Opportumty Employer MF/HC/ VET -l

a NRC Feem 306 U 8. NUCLEF KEEUL ATORY COMMI58 TON

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• . LICENSEE EVENT REPORT C ..R) f ACILITY NAME 01 DOCRET NUMBE R t2l PAGE '38 Wolf Creek Generating Station o l5 l0 l0 l0l 4l8 l2 i jorl0 l 4 I (l't'El let Lack Of Design Criteria Leads To Logic In Which Actuation Of A Fire Suppression System Affects Both Trains Of Safety Related Eauipment EVENT Daft 153 LER NUMBER ($1 REPOR Y DAf f (?) OTHER F ActLITit$ INVOLVED 181 MONTH DAf vtAR VEAR 5(Ojy(AL Q( voNiw OAy vgAp f acitet y N AMES DOCK E T NUM9t Al5i 015l0l0(o[ g l

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COMPLETE ONE LINE FOR E ACH COMPONENT F AILUR8 DESCRIBtD 44 TH18 REPORT H31 M^ C M' C OnfA Lt CAUSE SYSTEM COvPONENT E tO N8 DS CAUSE sv8 TEM COMPONENT pg g i I I I I I I I I I I I ! I l l l I l l 1 i l I i l I l EUPPLEMENTAL REPORY EXPECTIO (141 MONTH DAY VEAR SUSWSSION NES Uf ves. tometere (KPECVCO $Ugw$$10N CATli NO l l tSSTR ACT ILamut to 9400 sones o e , sooroveete'y Mreen smg'e soece troewertron knev 0et on March 14, 1990, following a discussion with personnel frm another utility, it was determLned that a Halon release in either Engineered Safety i Features (ESP) Switchgear Rom would trip both Class lE Electrical Bguipnent Air Conditioning Units. As an initial corrective action, the affected Halon release circuits were disabled and a fire watch was established for both ESF Switchgear Rocas. A permanent design change has been developed to alter the circuitry such that only the associated Air Conditioning Unit will be j secured in the event of a Halon release.

The root cause of this event was the lack of design criteria to clarify the train separation requiremnts of nonsafety related/special scope logic signals which actuate multiple trains of safety related equipnent. 'Ihe design criteria have been revised to include these requiranents. A review has been conducted of all circuitry potentially affected by this lack of design criteria. No additional design deficiencies were identified during the review.

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L IND G UCTIOi On March 14,1990, following a discussion with personnel fran another _

utility, it was determined that a Halon release in either Engineered Safety Features (ESF) Switchgear [JE] Rom would trip both Class lE Electrical Equipnent Air Cor ditioning Units [NA-ACU). As an initial corrective action, the affected Halon release circuits.were disabled and a fire watch was established for both ESF Switchgear Ro ms. his condition is being mysted 7 pursuant to 10CER50.73(a)(2)(v) as a cmdition that alone could have  ;

prevented the fulfillment of a safety function. ,

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i DESC3tIPTION OF EVENT t l

r On March 14, 1990, during a conversation with personnel fr m another utility, Wolf Creek Nuclear Operating Corporation (NCNOC) engineering  ;

personnel were notified of a potential design deficiency in that actuation 4 of the Halon Fire Suppression Systan in one ESF Switchgear Rom would trip the Class 1E Electrical Equipment Air Conditioning Units in both ESF.

Switchgear Roms. NCNOC engineering personnel subsequently corifW that the condition also existed at Wolf Creek Generating Station.. Per design documentation, one Halon release auxiliary relay contact fran each ESF '

Switchgear Room was wired to each of. the Class 1E Electrical Equipnent Air Conditioning Units auxiliary relays. mis wiring configuration would have resulted in a shutdown of both Air Conditioning Units in the event of actuation of the Halon Fire Suppression System in either of the~ESF ,

Switchgear Roms. Furthentore, this logic would. override the Class 1E Electrical Equignent Air Conditioning Units start signal that would be initiated by a Control Rom Ventilation Isolation Signal or a Ioad Shed/ Emergency Ioad Sequencer Actuation Signal.

At the time of this discovery, the unit was in Mode 5, Cold Shutdown. At approximately 1638 CST, the Halon Fire Suppression System Controls for both ESF Switchgear Ro ms were placed in inhibit and firewatches were established for the affected areas in accordance with administrative procedures. -As a i long term corrective action, a permanent plant nodification has been developed to make wiring changes to the Halon shutdown contacts. We wiring change will allow for a'Halon Fire Suppression System actuation to trip only the Class lE Air Conditioning Unit for the affected ESF Switchgear Room.

Following implemantation of this design change, the Halon control circuitry will be restored to operation. <

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'Ihe root cause of this situation was the lack of stated design criteria to clarify the train separation of nonsafety related/special scope logic signals which actuate the logic for mitiple trains of safety related equipnant. h design basis requirunent for isolation of the class lE Electrical Equipnent Air Conditioning Units was to ensure proper ESF Switchgear Rom Halm canoentraticn. 'Ihis requirunant was satisfied by wiring one auxiliary relay contact from each of the ESF Switchgear Ro m Halon release circuits to each Class 1E Electrical Equipnent Air Ccoditioning Unit. In the design of the Halon release circuit, the physical and electrical separation requirunents were met, but there was no design requixanent to check the circuit logic to confirm that there was no adverine train interaction. It was determined that the only affected circuits were those in which a safety related circuit would be actuated from a ncesafety related/special scope logic signal through an isolation device.

WCNOC engineering personnel have reviewed the schenatic diagrams and logic diagrams of all the auxiliary relays used as isolation devices. As a result of this review, it was ocncluded that no other similar design deficiencies exist at Wolf Creek Generating Station.

In order to prevent future occurrences of this nature, the design criteria have been revised to include a statement that system logic between nonsafety '

related/special scope circuits and safety related circuits mast be configured to prevent adverse actuations of multiple trains of safety related equipnant.

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l ADDITIGE IMGMhTIQ(

L h safety related function of the Class 1E Electrical Bauipnent Air

Conditioning Units is to operate in a continuous recirculation node to maintain the ESF Switchgear room, the battery rooms, and the DC Switchgear

roms at or below the design taperature. While the refrigeration subsysten is in operation, the anount of cooling provided is self-regulated by the Air l Conditioning Unit control circuit. 'Ihe principal control functions are provided by a taperature switch / step controller which autmatically starts and stops the Air Conditioning Units as required. Indicaticn of a loss of preferred AC power, or a loss-of-coolant accident will autmatically <

l initiate the Class 1E Electrical Equipment Air Conditioning System if not-already in operation. However, the design function of this system was overridden by a Halon release in either of the ESF switchgear roms, associated battery rooms, or associated DC switchgear roms. By making the Nae ,- mm...

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0l012 l- 010 014 oF 0l4 vio,, . ,. .c, - wim wiring changes, the syntan will then be designed par the original operational intent and thus cnly the Air Conditioning Uni'c associated with the rocan in which a Halon release has occurred will be stopped.

An evaluation of the consequences of a fire or a false actuation in one of the ESF Switchgear Rooms has determined that no significant adverse offacts would have occurred to prevent the mitigation of an event. Although both Air Conditioning Units would have been removed fran service, once the fire had been extinguished, the Halon systan would be reset per p.vcidure. By resetting the Halcn Systan, both Air Corditioning thits would be returned to service.

'1here have beeng previous similar occurrer.m.

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