ML20024G503

Submits Results of Review of Control Circuits of Safety Related Equipment in Response to

ML20024G503
Person / Time
Site:	Monticello
Issue date:	02/20/1973
From:	Mayer L NORTHERN STATES POWER CO.
To:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9102120577
Download: ML20024G503 (4)

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MSRB NOMTHERN 5TATES POWER COMPANY MIN N E A PO Ll e. MIN N E S OTA 99400 February 20, 1973 Q)

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$J; Mr. D. J. Skovholt 9-FE8231973 m Assiotant Director for Operating Reactors Directorate of Licensing L. o.l.

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Y United States Atomic Energy Commission

',y-f g-Wachington, D.C.

20545 4i: er (v

Dear Mr. Skovholt:

'u MOUTICELLO NUCLEAR GUTERATING PIJJIT DOCt1T NO 50-263 LICDiSE NO DPR-22 Review of Control Circuito of Safety Related Equipment The resulte of the review are being reported in responte to your letter dated Ibcember 22, 1972, which cited two cases of control circuit deficiency and requested a review of the control circuits of all cafety related equipment at the plant to accure that dienbling of one component does not, through interlocke or coquence control, cause inoperability of other components.

The first control circuit deficiency cited in your letter, pertaining to the l

interlock which prevents two redundant Standby Liqui.d Control System pumps from operatics concurrently, var known prior to receiving your letter. The interlock was provided by use of auxiliary "b" contacte of the pump motor startere which reculte in dicabling of both pumpo when either motor etarter is in the racked out pocition. Operating ordere had been iccued to secure that neither standby liquid control pump motor starter would be racked out of the operating position without the operator electrichily defeating the interlock. The motor control center eclle, in which the otandby liquid control pump motor starters are l

located, vere also concpiciously marked with instructions to defeat the interlock j

immediately upon removal of either motor starter.

We had also previously investigated the pocsibility of interlocks accociated with the Reactor Building Ventilation cupply domper control circuitry and found no cuch deficiencies as in the recond cace you have cited.

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IE FEB 231973 5" 3 I

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UAtt ECTION 6 ; 6 t

b NCW CLERK 126 s

a 9102120577 730220 CD PDR ADOCK 05000263 p

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NORThwRN OTATEC POWER COM.ANY 4

I Mr. D. J. 3kovholt Pace 2 February co,1973 1

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l We have, with the participation of General Electric, reviewed the following list of nuclent steam supply safety related cystems and have verified them to be free of dicabling interlocke.

a) Reactor Protection System b) Nuclear Steam Supply System Icolation or Shutoff System c) Core Standby Cooling Syrtemt Core Spray IJCI e

IIPCI ADS i

d) !!PCI/RCIC combination for vecrel vater inventory control after coolation of reactor versel, c) Standby Liquid Control System (rith the exception of the pump interlock noted above)

All of the above cysteme are decigned cuch that redundant cubeystems can operate concurrently, with the exception of the SLC pu.tpc previously considered, and the removal of circuit breakers or other componente from any one cubrystem vill not dicable the redundant counterpart.

Safety related cystems not designed by General Electric have been reviewed, vith arsistence from the architect-engineers, and have been found to be free of dirabling interlocks. The sycters and equipment reviewed include:

a) Standby Gas Treatment Syctem b) Primary Containment Icolation System c) Reactor Building lleating and Ventilating System (including inlet and exhauct fan and damper controle).

d) Standby Power Load Shedding Control e) Service Water Control Syctem for RIIR and IIIt'I f) Standby Ibergency Dicecl Generator Starting and Loading Control l

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.RN OTATC POWER CON ANY l

Mr. D. J. Okovholt Page 3 February 20, 1973 In addition, all h.16KV station auxiliary bus cource breaker controle and escential 400V bus source and load supply breaker controls have been reviewed for interlocks that might have cafety implications. Ac with the General Electric designed cafety related systems, redundant systems are designed to be operated concurrently and the removal from service or disabling of one or more components in a cyetem vill not ef fect the operability of the redundant counterpart.

i Present policy requires that when cyctems or componente are deliberately made inoperable for maintenance, required operability demonstration of backup equip-ment thould be perfomed prior to disabling the affected system or component.

Thced on the control circuit review reported in thic letter and pact experience in tecting redundant systems with componente dicabled, we believe there is adequate assumnce that dicabling a portion of a redundant system vill not render another component inoperable, and repetition of operability demonstration after dirabling a podion of a redundant system is not necescary.

Yours very truly, h.

p L 0 Maye r, P. h.

Director of Nuclent Support Cervices LOM/SJK/dm cc:

B 11 Grier I

C Charnoff Minnesota Pollution Control Agency Attn.

K Daugan i

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AEC DISTRID'.fTION FOR PART 50 DOCXET MtCERIAL (TEMPORARY FOM)

CONTROL NO:

1260 FIII FROM DAW OF DOC:

DAL ' REM ' LW 12Mg RPf an Northern States Power ComMn.s Minneapolis, P.innesota 55kQ1 L o Mayer P-20-73 2-23-73 X

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