ML17037C463

Letter Confirming That Niagara Mohawk Will Establish by Monday, March 1, 1976, a Differential Pressure of a Minimum of One PSI Between the Drywell Atmosphere and the Torus Vapor Space

ML17037C463
Person / Time
Site:	Nine Mile Point
Issue date:	02/27/1976
From:	Rusche B Office of Nuclear Reactor Regulation
To:	Rhode G Niagara Mohawk Power Corp
References
Download: ML17037C463 (6)

Text

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Docket NRC PDR Local PDR ORB¹3 Rdg KRGoller Docket Ho. 50<<2?0 TJCarter

'Lear CParrish JJiagar a mohawk Power Cor poration JGuibert ATTW: )lr. Gerald K. Fhode . OELD Vice President - Engineering 'I8IE (7) 300 Brie Boulevard 3feat DE I senhut Syracuse, dew York 13202 TBAbernathy JRBuchanan Gent,ler.en: ACRS (16)

BE: l/ino Nile Point., Unit 1 As a rosuit of a recent additional asscasnent of the structuraj, integrity of the lfark I contairment syste~ used in your reactor facilit,y, @embers of our respective technical staffs net in Bethesda on February 26, 1976.

"<<his letter will confim t,he results of these discussions and tho conclusions reached by the HBH staff subsequont,, to the nieeting.

On January,28, 1976, the tfark X owners group specified that the torus support downward load strength,ratios were based on an clastic analysis. Hatios around 1.0 vere not of great concern to you because you believed that a redistribution of loads would occur and that these factor " would be reduced when an ela tic-plastic analysis waa later per forr>ed. On those facilities wit,h strength ratios greater than 0.9, the NHC staff requested furt,her infort..ation which we are currently evaluat.ing.

On << ebruary 19 and ZO, 1976, a nore detailed discussion of the above t,echnical points occurred. After studying details of the st,ress distribution fro: Pcchtel s computer outp>>t, it's our judgment, and your con ultant,s agree that. redistribution of loads r:,ay not.

be significant, for thc wclds at tho top of thc torus columns.

'<<herefore, the r.;argin 'of safety at, these velda are lower than those for other'"lark X components.

Because of this reduced var"xn, the r.cct.in,", in Petheada r 5 called t,o discuss your plans to promptly r ostore a<equate nar;;inc of safct,y for thc'atruct,ure. You <<-.'cscribed and discussed with our staff various oper'atinp r odifications which would reduce the loads, such as usc of an increased dryveii pre.".sur,e and decreased torus

>uter level. Aft,er discussing your planned actions and t,he length of ti:.:e required to provide enhanced safety'Tar~ins usin,", thc, operational actions, you and other r.cnbers of thc t.'ark E o.ner" OPPICC~

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Niagara Vlolw~lc Power Covporation - 2 <<

J group indicated that you ~jould prompt,ly enhanco safety narpinb by pvessuvinG the containnont to establish a difforontial pressure of at loaat 1 psi bot~rcen tho drytrell atmosphere and torus. You proposed to assur o that. such differential was established by Vonday, Birch l, 1976.

Our tochnical staff hao assessed this pvopoaal and aIrvce srith your tcchnioal repreocntativoo that the eotabliatment of a differential preosuro of at leaot l pai >ril'1 provide a rcduotion in potential loads during a postulated loss of coolant aocidont and an associated restoration of the margins of oafoty so that, the margin of safety is about a facto of'rio.

1'n pleased. with the prompt response by the Uyvk X owners'roup, to our concern that safety nargino be rest.orcd in a pronpt fashion, This, therefore confirao our discussions of yesterday that you will establish by Vonday, lLarch 1, 1976, a differontial pressure of a minir1un of one psi between tho drywell atmosphere and thc torus'apor space and that this differential pveaoure ~rill be naintainod >>hencvor tho rcactov io in oporat;ion, until furt,her author ization by the NBC. 7hia,1rill reopond to our directive of yesterday 'that safety margins for tho 'ot;vucturc bo enhanced progptly.-

Gone of t,he oyotcno may be modified thereafter by a p1r1pback syates to- nininize t,he nit.rogcn requircrlento. Ouv staff will revietr ouch proposal promptly vhon your plans become moro definite. 'ny

-. 'oroovev, Mc also ~rill continuo to work (~1th your staff on prcnpt

'; inp3.er1ontation of your plants for ot,ructur al dodlficationo of the contairL~ent aystcr1o in accordance ~.ith tho oatabliahcd program

, of t.hc Hark I ouner." group.

Sincerely, Bcn C. Buachc, Director Offioc of t;uclcar ficI1otov Ilopulatfon cc; Sce nc.":t. pago OSSICC~ .,DOB,.;,QBB.-...2 ....,.. GELD........,....;....... NRR.:DIR..

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Niagara Mohawk Power Corporation - 3 CC:

Arvin E. Upton, Esquire LeBoeuf, Lamb, Leiby g MacRae 1757 N Street, N. W.

Washington, D. C. 20036 Anthony Z. Roisman, Esquire Roisman, Kessler and Cashdan 1712 N Street, N. 14.

1(ashington, D. C. 20036 Dr. Nilliam Seymour, Staff Coordinator New York State Atomic Energy Council New York State Department of Commerce 99 Washington Street Albany, New York 12207 Oswego City Library 120 E. Second Street Oswego,. New York 13126 Mr. Robert P, Jones, Supervisor Town of Scriba R. D. 84 Oswego, New York 13126

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