ML20058K518

Discusses Two Incidents at Plant Indicating Deficiency in Control Circuit Design That Warrants Review of Control Circuits of All Facilities to Assure That Deficiencies Do Not Exist or Corrected

ML20058K518
Person / Time
Site:	Monticello, Oyster Creek
Issue date:	12/22/1972
From:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
To:	Dienhart A NORTHERN STATES POWER CO.
Shared Package
ML20058K522	List: ML20058K518 ML20058K526 ML20058K529
References
NUDOCS 9102110352
Download: ML20058K518 (2)

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• Decenber 22, 1972 Docket No. 50-263 I

I Northern States Power Company ATTN:

Mr. Arthur V. Dienhart Vice President of Engineering 414 Nicollet Mall Minneapolis, Minnesota $5401 Gentlemen:

Two incidents have occurmd at a nuclear power plant that indicate a deficiency in the control circuit design that warrants a myiew of the contml circuits of all facilities to assure that these types of deficiencies do not exist or am cormeted if they do exist

~ incidents involved the inadvertent disabling of a corponent by rack Both out'the circuit breaker for a different component.

this capability was mquired. caused the loss of capability to isolate sec3 In the second case service but also its redundant counterpart.a bmaker for one msulted from the use of auxiliar/ contacts on the rovable portion ofBoth of i

1 the circuit breakers in the control circuits of other co::ponents the breaker is racked out,'the control circuit er: ploying these conta t When t

is opened and may be rendered inoperable.

cs mports en these two occurrences am enclosed for your inforration.A co

'Ibe licensee's corrective naasures for both of these case mdesign of the contml circuits so that racking out the breakers would not render the contml circuits of other equip::nnt inoperable.

As a msult of these occurrences, we mquest that you perfom a revi 1

of the ecntrol circuits of all safety related equip::ent at the plant ew to assure that disabling of one cc::ponent does not in other interlocking or sequencing controls, render other components inoperable.

All redes of test, operation breakers had not been included in the failure rode control circuits.

e Also, your procedures should be reviewed to ensum they provide that whenever part of a redundant system is removed from ser/ ice, the por tion remaining in service is functionally tested irrediately afte disabling of the affected portion and, if possible, before disabling r the of the affected portion.

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'b.e msults of your myiew am mquested within sixty days. 21s infonmtion should be pmvided with one ciped original and thirty-nine additional copies.

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Sincemly,

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/ rsh b Y Dinald J/Scovholt Assistant Dimotor for Operating Beac*Ars Dimotorate of Licensing Enclosums:

Licensee's reports an occurances cc: Gerald Charnoff Shaw, Pittman, Potts, Trowbridge & Madden 910 - 17th Street, N. W.

Washington, D. C.

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