ML20004F757

Interim Deficiency Rept,Originally Reported on 810514,re Design Deficiency in 120 Volt Ac Vital Power Panelboards. Design of Neutral Block Attachment Screws Modified.Final Rept by 810815

ML20004F757
Person / Time
Site:	Diablo Canyon
Issue date:	06/12/1981
From:	Crane P PACIFIC GAS & ELECTRIC CO.
To:	Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8106220287
Download: ML20004F757 (2)

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PACIFIC OAS AND ELECTRIC CCMFANY P, O. 80x 7442 . 77 BE ALE STREET,31ST FLOO R. S AN FR A NC'$00, C ALl/0 R NI A 94:C6 yg '

TE LE PHO N E (415) 7 814 211 TELE 00Pl!M (415) 543 7813 June 12, 1981 W CD Mr. R. H. Engelken, Direct:or 8 cp Office of Inspect n and Enforcernent (Th/ A 'h Degicn V $, Nf.l))J f -

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• " J Walnut Creek, CA 94596 ho M. Docket No. 50-275 N Docket No. 50-323 4 '

Diablo Canym Units 1 and 2 10 CR 50.55(e) Report - Potential Ostficiencf-Ctmceming the 120 VAC Vital Power Panelbocdi

Dear Mr. Engelken:

On May 14, 1981, Pacific Ces and Electric Ccnpany report.au a possible 10 TR 50.55(e) reportable occurrence at the Diablo Ca:r/cn Nuclear Power Plant concerning an apparent design deficiencf in the 120 Vac vital instrtunent power supoly panel no. PY13. This electrical panel is a Federal Pacific Electric Cb. Wai NA15.

The eppfumt design deficieref was noted when an electr%r1 was makim a teminaticn at the neutral bloer. in panel FY13. This acticn caused the neutral block to becnne detached frmt the neutral bus.

Once detached the 120 VAC circuits in this panel were open-circuited causing the devices powered frat this panel to W deenergized. This neutnl block becme detached because crwt of the t:e screws attaching it to t'a neutral tus had actne free and the second screw was loose. The one rernaining loose screw could not withstand the forces exerted by the '

electrician and the neutral block separated i'rcr: the neutral bus.

i 8106220 W s (( sp i

t-O Mr. R. H. Engelleen Jtme 12, 1981 1his situatim was in==14mtaly almW in the control rocm indi-cating a loss of this 120 VAC vital power source. At this time, the panel was doenergized and the neutral block was repaired. 'Ihe repair was dis-aussed with the PGandE Electrical Engineering Department and ths problem referred for their investigation and resolution.

n=r-anna there are four separate 120 VAC vital power supplies thers was no m2 verse effect cm plarzt safety as a consequence of the failure ,

of this power supply. J We have dar-hw to 1:: prove the design of the neutral block attach-monts and are in the process of nodifyinJ them. As these :mx11ficatims are umb, and in order to evaluate any potential problems, the cccstructicn staff will remove each neutral bus and deehe the status of the attach-ment screws in all other Unit 1 and Unit 2120 vr vital panels. Cmcn this deteminaticn is atzpleta, we will provide a final report presenting our i findings and evaluaticm of this situaticn. ,

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'Ibe final report should be complete by August 15, 1981. Should the final repcat irdicate that an Atual design deficie.Ty exists, we will Irv-1nh in the final report the additional regn: ting infor:::aticn required by 10 e n 21.21.

Very truly yours, PHILIP A. CPX G , JR.

Aic: Director Office of Inspection and Enforcanent U. S. Mv-laar Regulatory Ocmnissicn Washingtcn, D. C. 20555 Service List '

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