ML20086L815

Special Rept 91-005:on 911112,invalid Failure of Emergency Diesel Generator B Occurred During Train a Safeguards Actuation Test.Caused by Binding of Temporary Test Flag in Alternate Supply Breaker Cubicle.Test Flags Modified

ML20086L815
Person / Time
Site:	Wolf Creek
Issue date:	12/12/1991
From:	Bailey J WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
91-005, 91-5, NO-91-0339, NO-91-339, NUDOCS 9112170089
Download: ML20086L815 (4)

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W#) LF NUCLEAR CREEKOPERATING John A Baney Vica f*reedent ofere1*C+s December 12, 1991 NO 91-0339 U. S. Nuclear Regulatory Consnission ATTN Document-Control Desk Mail Station P1-137 Washington, D. C. 20555

Subject:

Docket No. 50-482: Special Report 91-005 ,

The attached Special Report is being submitted in accordant.e with Technical Specification 4.8.1.1.3 ana 3.9.2 concerning an invalid f alltsre of Emergency Diesel Generator "B'.

Very truly yours. ,

d olm a ./ %

John A. Baile Vice President Opetationn JAB /aem Attachment eca A. T. liowell (NRC), w/s R. D. Martin (NRC), w/a G. A. Pick (NRC), w/a W. D. Reckley (NRC), w/a L

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InvJJd Failure of yearrptev Dietwil Oterator "B,5 ,

his report doncribes ao invalid fallure of Ehergency nlesei Gweretar (FIG)

"B" which occurred ch thv:ter 12, 1991. '11 tis Itprt is teing surmtitted in accordance with 'Itchnical SpecifJcatices 4.9.1.1.3 arc 6.9.2.

mWCRIMION & EVD'f@

On Novanher 12, 1991, section 5.4 of surveillince procedute S'IS 10-001B

" Integrated D/G and Safeqt. ants Ivratien %st 'Prain B was being perfornal. ,

his setion of the proccduru sinulates a loss of offsite pomr aM'verifles the 'EOG 'will autmntically start, attain tJm rugulred voltage and fsplency, -

e.nd energize the stergency bus withih 12 soccnis. At 1045 hours0.0121 days <br />0.29 hours <br />0.00173 weeks <br />3.976225e-4 months <br />, the sumilated loss of offeite power es liutiated by att operator pressing an under-voltaga test button. ECG "B" started and obt.uined the regtdred var: 3ge

• and fregtxricy, but fhe EDG o;tput brtvQer did not close to energize errrgency  ;

tus NB02._ The EIG vas secured and the appropriate Schnical Specification acticn stacnnants and off-norm 1 proceduruc wert entered for 1:;st of NB02.

Electrical malntenance perscruel begui .to Jnvestigata the rmuon for the failurn. , Meturwhile, operatora attempted to rv-energize NB02 fmu.its rnael supply. Itunar,.the nonnal supply bmaker also would not close to enenjize the bus.

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.fi B.m NB01 can to supplieri fmn rhme sources: the nra ral supply, tl'a r2 ternate g supply, or JX; "B" . 'Ihe alternate arpply breaker is placed in a closed test I L pos!. tion for this test in order to verify the brmker opens when an l

uMerwitage conrtition occurs.- hithough the bnnkar aponed, a switel which

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' _ pa;vides g*;1 tion indicatitt4 to the bruker icgic circuitry still indicated the break e was c'.osed. his pmvented the IIX, output bmaker and tne unal supply breaker frun closing oneo the hos.

1 Af ter the altnr, ate sulply breakeL 9as taken out cf its test aligranent, Joperators were abl9 to close the,nor:ral supp3r brmker and re-energize NB02 at <

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1134 hwrs. Idditional revie; of tio avuat was conducted aM at- 1604 hours0.0186 days <br />0.446 hours <br />0.00265 weeks <br />6.10322e-4 months <br />, EDG "B" wet successfully kaded onto bus NB02 to fulfill the requirulents of

-trntion 5.4 of the sutveillance proc.22ure.

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.i H00tf CMM M_D_LCeRfC"IK M7ED i ne root cause of this wem ma binding of a taporary test flag installed in

, the alternate supply brmkg r cubical for this test. _ Prior _to this test, tus-NB02 was being energized by its norm 1 supply. Its alternate supply breaker' vas. " racked down" (disconnectai frun the bus). In onkar to verify the alternate supply breaker would open if EDG "B" was required to energize NB02, a test flag and test junper were installed. % e test flag allus a plunger on. ,

the breaker to activate a position switch plunger wtam the bnuker is: racked-down :(when the-brmker is racked up the brmker plunger. is in contact with the switch plunger). no test flag is a rnetal red which slides along a guide past von the switch fram -(see attached diagram)._ Nhen the p

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At.tacteunt. to M) 91 -0339 IWJe 2 of 3 brmkor is closod, the htmker plurgar ext 4nis upward and the test f]ag pushes tho witch plunger up*ud. When the bimkor cpans, the breaker plunger drops. A spring on the witch plunger, along with the weight of the test flag, allcus the switch plunger ard the test flag to drop with the brmkor plurger.

During this test, hcuuver, ocso birding along the geldo Imt provented the

tmst f. lag f zun ritqving cenpletely when the breaker opened. 7his left the switch plunger in an intornullatu positico and the witch still hilcatcd tio htmkor clomd. 7herefom, the ansociatrd logic circuitry did not allow the EDG output bnnker or the nornal supply bronker to closo and energize the bus.

1b prevent similar oamts f rten occurinng in a.o futxra, the test flags have been slightly nrdificd to allcw for n.1 ior adjurtuents in thur alignnent.

7his will pmvesit, bliaitng of the test fla? and ensure the poMtion switch

.:orrectly mila ts the actw 1 resition of the bituker during testing.

i FAUlHH Q_Ngj]flgggM atergency bus NB02'a nitea ate supply bnnke. not part of the EDG unit as defincd in Regulatory Guide 1.100 aut IEEE f . Aid J87-1984. In addition, the tese cq11 1 mant descritni in this report a not nontally installcd and, theretom, would not af fect operatic.n of the camugmicy bus alternato supply breaker during norral or mergency operating conditions. Thorofore, the failuru of the EDG output breaker to closo, as ItxIulnd by the surveillanco pmecdum, in not censidend a valid test or failum in accordance with paragraph C.2.o.(2} of Regulatory Guide 1.108. An a result cf this evera., EtG "B" was declared in:qurablo for a pariod of 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />, 39 n'inutes.

Ubis invalid fallum does not affect the current surveillance test interval of 31 days as required by Table 4.8-1 of Technical Spec 1rication 3.8.1.1.

Yhtough Ibvcntor 12, '.991, there have txn four valid failums of EDG "B" in

the .last 100 valid testa. Prtni the tino of the last valid failure of EDG "B" on Docmler 9,1989, KG "B" has undergone 33 successful valid tests. The g last invalid failum of EDG B" occurred on August 19, 1991 (Special Report j 91-003).

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,Attadustt in K) 91-0339

'. nwjo 3 of 3 awitch _

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_. ,, switch plunger

. .-- breaker plunger

/ X breaker Breaker Racked Up (connected) i switch f guide post ,

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i teat ag l

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/ ,- . A 10eaker u - __

aroakor Racked Down (disconnected) with Test Plag in place

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