ML17037C463
| 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
Docket Ho. 50<<2?0 JJiagar a mohawk Power Cor poration ATTW: )lr. Gerald K. Fhode Vice President - Engineering 300 Brie Boulevard 3feat
- Syracuse, dew York 13202 Gent,ler.en:
DISTRIBUTION:
Docket NRC PDR Local PDR ORB¹3 Rdg KRGoller TJCarter
'Lear CParrish JGuibert OELD
'I8IE (7)
DEIsenhut TBAbernathy JRBuchanan 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
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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
'ny ouch proposal promptly vhon your plans become moro definite.
-. '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~
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POINI hBC-318 (RST. 9-55) hECM 0240 0 IIISI OOVSIINMNNl'tIIINTINOOIXIOP IOTA 444 144
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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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