ML20064F235

/01X-0 on 781108:a Field Mod Was Made to Vessel Lower Head Insulation & the Mod Was Not Seismically Analyzed IAW FSAR Due to Personnel Error.Subsequently Analyzed by Stone & Webster & by Westinghouse

ML20064F235
Person / Time
Site:	North Anna
Issue date:	11/17/1978
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
Shared Package
ML20064F229	List: ML20064F225 ML20064F235 ML20064F241 ML20064F253
References
LER-78-100-01X, LER-78-100-1X, NUDOCS 7811280325
Download: ML20064F235 (2)

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S 60 61 DOCKET NUMBER 68 69 EVENT DATE 74 75 REPORT DATE 80 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h 10121 l A field modification was made to the rancent vaaaal inwar hand inci>1 =ri nn , which i= i O 3 l supported by the incore instrumentation nozzles. and the modification was not sein- l 0 . lmically analyzed as required by the FSAR. This event in renort abl e nn nor T 3 - l l0Isi l6.9.1.8.i. I 10161I I 10171 I I I

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33 36 31 40 41 42 43 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h l i l 0 l lThe field modification was not seismically analyzed due to personnel error. We s tinst- l~

i i [ house and Stone & Webster subsequently performed a structural analysis on the incore I g .,j l tubes. Analysis results indicated that, in the event of the worst case earthquake, as I

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[ q 3 l lmany as 6 incore instrument tubes may yield, but the structural integrity of the tubes l lil41 ]would not be violated. A new modification is presently being developed. l 7 8 9 80 ST S  % POWER OTHER STATUS IS OV RY DISCOVERY DESCRIPTION Vendor li15l(Z)@ l0l9l7l@l_

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. Vi'rginic Electric cnd Powar Corptny North Anna Power Station, Unit #1 Atta:chment: Pago 1 of 1 Docket No. 50-338  :

Report No. LER 78-100/01X-0 1 1 Event Description  !

A field modification was made to the reactor vessel lower head insula-tion, which is supported by the incore instrumentation nozzles, and the modification was not seismically analyzed as required in the FSAR. This event is reportable as per T.S. 6.9.1.8.i.

Probable Consequences of Occurrence .

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The FSAR requires all Class I structures to be seismically analyzed ,

to ensure the safe operation and control of the plant during a seismic  ;

event.

A detailed analysis by Westinghouse and Stone and Webster shows that the continued operation of Unit 1 is acceptable due to the fact that the structural integrity of the tubes will not be violated for the postulated i b, seismic conditio..s of the FSAR.

• In the event of the occurrence of a seismic event prior to modification, I there would be no effect on the health and safety of the public.

Cause of Occurrence The original design of reflective type insulation would have interfered with the installation of supplementary neutron shielding. A field modification was made to the ' insulation to relieve this interference, but due to personnel error, the modification was not seismically analyzed. '

Immediate Corrective Action Westinghouse, Stone and Webster and Transco performed a structural.  !

! analysis of the insulation. ,

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It was found that, in the event of the worse case earthquake, as many as 6 in-core instrumentation tubes may yield, but the structural integrity of '

the tubes would not be violated.

Scheduled Corrective Action At the. present time, Westinghouse and Stone and Webster are developing a modification to the insulation which will be installed at the first refuel-ing on Unit #1.

Actions Taken to Prevent Recurrences No further action is required.

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