ML19276E077

Final Rept Per 10CFR50.55(e),re Failure to Seismically Analyze Field Mod to Reactor Vessel Insulation.Westinghouse & Stone & Webster Changed Reactor Vessel Insulation Support Structure to Prevent Incore Instrumentation Tube Stress

ML19276E077
Person / Time
Site:	North Anna
Issue date:	02/27/1979
From:	Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
456C, NUDOCS 7903020291
Download: ML19276E077 (1)

Text

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February 27, 1979  ;

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Mr. James P. O'Reilly , Director Serial No. 456C Office Inspection & Enforcement .PSE&C/MLM:adw:mc  :

U. S. Nuclear Regulatory Comission i Region II Docket No. 50-339 101 Marietta Street, Suite 3100 3 Atlanta, Georgia 30303

Dear Mr. O'Reilly:

In accordance with 10CFR50.55(e), NRC Region II was notified on August i 3,1978 that a field modification which was made to the reactor vessel in-sulation on North Anna Unit 2 had not been seismically analyzed. [.

Interim reports were submitted to NRC Region II on September 1, 1978 and f November 10,1978 (Serial No. 456A and 456B, respectively) stating that the  ;

i clips which support the reactor vessel insulation may exert excessive forces on the incere instrumentation (ICI) tubes in the event of a worst case earth-  :

quake. It .<as determined that as many as six ICI tubes may yield, but the structural integrity of the tubes would not be violated.  !

( 1 Westinghouse and Stone & Webster have redesigned the reactor vessel in-sulation support structure to prevent overstressing of the ICI tubes. The structure ~ consists of a frame which supports the bottom reactor vessel insula-tion assembly. The frame is attached to the inside surface of the neutron shield '

tank. The loads from the insulation lower head are transmitted to the frame via clamping devices which attach the lower head insulation to the support frame. The  :

clips presently attached to the ICI tubes which have caused the overstress condi-  !

tion will be removed following installation of the new support frame. Unit 2 in-stallation will be completed prior to initial fuel load.  ;

We consider this to be the final report under the provisions of .

10CFR50.55(e). Please contact me if further infomation is required.. '

Ver tru yours, Sam C. rown Jr.

Senior Vice Presi ent - Power Station Engineering and Construction cc: Mr. John G. Davis, Acting Director n Office of Inspection & Enforcement Q

Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation

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