ML20010G093

Final Deficiency Rept Re Inadequate Design of Reactor Pressure Vessel Support Skirt Access Hole Cover Plates, Initially Reported on 810129.Covers Will Be Replaced W/New Ones Capable of Withstanding Annulus Pressurization Loads

ML20010G093
Person / Time
Site:	Nine Mile Point
Issue date:	09/01/1981
From:	Rhode G NIAGARA MOHAWK POWER CORP.
To:	Brunner E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8109150317
Download: ML20010G093 (2)

Text

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6e.38(e)

• t Y NIAGARA

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NUMOHAWK NIAGARA MOHAWK POWER CORPORATION /300 ERIE BOULEVARD WEST, SYRACUSE, N Y.13202/ TELEPHONE (315) 474-1511 September 1,1981 Office of Inspection and Enforcement Region i Attention: fir. Eldon J. Brunner " co s

d // cr Acting Director ,

Division of Resident and Project Inspection g ,

U.S. Nuclear Regulatory Connission 8(r 0*

631 Park Avenue ~

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A King of Prussia, PA 19406 'I 8

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Dear f1r. Brunner:

y 4 Re: Nine Mile Point Unit 2 b q Docket No. 50-410 T/f This letter is subnitted as a final report in accordance with 10CFR50.5S(e) for a condition involving the design of the Nine 1111e Point Unit 2 reactor pressure vessel support skirt access hole cover plates. This condition was initially reported as a potential deficiency on January 29, 1981.

Our interin report dated liarch 13, 1981 indicated that the reactor pressure vessel support skirt access hole cover plates as currently designed may not be adequate to withstand the newly identified loads of a LOCA annulus l

pressurization event. The New Load Program Annulus Pressurization Analysis has verified that the access hole covers, nade of 1/4 inch plate, may fail under annulus pressurization loading.

A preliminary analysis based on the review of design drawings by our nuclear steam supply systen vendor indicates that this condition is not a safety concern. This prelininary 1ysis indicates that since the cover plate centerline is nearly the sai. as 'the point where the control rod dri'res are welded to the reactor pressure vessel, the strength of the control rod drive housing / reactor pressure vessel interface area far exceeds the possible load from the cover plate inpact. Therefore, rod insertion is assured and no l

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ib 8109150317 810901 PDR ADOCK 05000410 S PDR

Septerher 1,1981

• Page 2 adverse safety affects would occur from this event. However, a detailed analysis would be required to provide sufficient assurance tSat the results of the preliminary analysis are correct. Therefore, in consideration of the most cost-effective, technically acceptable approach, the existing reactor pressure vessel support skirt access hole covers will be replaced with .new ones made from thicker plate capable of withstanding the annulus pressurization loads.

Ver/ truly yours, HIAGARA H0 HAWK POWER C0 P0 RATION s

aidK'.Rh e Vice President System Project Management PEF:bd xc: Director of Inspection and Enforcement U.S. fluclear Regulatory Connission Washington, D.C. 20555