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

.

4 VepCO

__. m c m c _ _ _ _. _ _. _ _. _

February 27, 1979 i

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

@h Office of Nuclear Reactor Regulation

\\

790302 02S/

3 a

misemi,,in,,,,--mm-min.umi-nei.im-m-.m= = - - -in.==emmhimumi

m'