ML20041D656

Forwards LER 82-003/01T-0:Detailed Event Analysis Encl

ML20041D656
Person / Time
Site:	Oconee
Issue date:	02/16/1982
From:	Parker W DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20041D657	List: ML20041D656 ML20041D658
References
NUDOCS 8203080551
Download: ML20041D656 (3)

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Vict PerssOENT IELEP=O=g: Anta 704 5' taw Paoouctio" February 16, 1982 73-do8' to e' Cb Mr. James P. O'Reilly, Regional Administrator U. S. Nuclear Regulatory Commission 8 Region II NECEIVED 101 Marietta Street, Suite 3100 g7 Atlanta, Georgia 30303 MAR 0519825 dl Re: Oconee Nuclear Station T kT{p &

res Docket No. 50-270 4 /

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Dear Mr. O'Reilly:

Please find attached Reportable Occurrence Report R0-270/82-03. This repert is submitted pursuant to Oconee Nuclear Station Technical Specification 6.6.2.1.a(9), which concerns the discovery of conditions not specifically considered in the safety analysis report or Technical Specifications that require corrective measures to prevent the existence or development of an unsafe condition, and describes an incident which is considered to be of no significance with respect to its affect on the health and safety of the public.

Ver truly yours, 1

AWilliam - O.u. Parker, J JFK/php Attachment cc: Director Records Center Office of Management & Program Analysis Institute of Nuclear Power Operations U. S. Nuclear Regulatory Commission 1820 Water Place Washington, D. C. 20555 Atlanta, Georgia 30339 c

Mr. W. T. Orders h1C Resident Inspector Oconee Nuclear Station i

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DUKE POWER COMPANY OCONEE NUCLEAR STATION UNIT 2 Report Number: R0-270/82-03 Repert Date: February 16, 1982 Occurrence Date: February 2, 1982 Facility: Oconee Unit 2, Seneca, South Carolina Identification of Occurrence: Fuel assembly broken holddown springs Conditions Prior to Occurrence: Refueling Shutdown Description of Occurrence: On February 2, 1982, a broken holddown spring (HD spring) was discovered on Oconee 2, Batch 7 Fuel Assembly #01K3 during video inspection of the Oconee 2, Cycle 5 core in the Spent Fuel Pool.

'" Subsequent inspection identified broken HD springs on Oconee 2, Batch 7 Fuel Assembly #0lJC and OlKX, and Oconee 1, Batch 4 Fuel Assembly #00G0.

-Apparent Cause of Occurrence: The apparent cause of the broken springs is fatigue-induced cracking at an existing surface flaw which then propagated by fatigue. Analysis of unirradiated samples, from the same heat as the

'- broken springs of the Oconee 2, Batch 7 Fuel Assemblies, indicate that this heat has good resistance to stress corrosion cracking, which was the apparent cause for the previous HD spring failures reported in R0-269/80-15 and submitted by letter of W. O. Parker, Jr. dated June 6, 1980. Analysis of unirradiated samples for the Oconee 1, Batch 4 fuel assembly spring is not available; however, available data indicates that this HD spring also had good ~ resistance to stress corrosion cracking,and the apparent cause of the failure is the same as the Oconee 2, Batch 7 HD springs.

Analysis of Occurrence: The safety implications of operation with broken HD springs was adequately addressed in R0-269/80-15, which is repeated here.

The spring failures pose three potential concerns: (1) loss of holddown force; (2) loose parts; and (3) interference with normal CRA movement.

Analysis of these potential concerns has eliminated any reasonable safety questions.

With regard to loss of holddown force, Babcock and Wilcox has confirmed analytically that reactivity increases due to reinsertion of a " lifted" assembly add less than 0.01% Ak/k per assembly. No lateral movement would result from lift since positive lateral restraint is provided through core internal structures. Lastly, no cyclic lifting / reinsertion is expected since one break in a spring reduces holddown force slightly allowing the assembly to remain in place, and two breaks reduces the force to essentially zero, pinning _ the assembly in the lif ted position.

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R0-270/82-03 Page 2 Loose parts pose no additional safety hazard but are simply operational problems. All the spring breaks have occurred in one or both of the interface regions between the compressed and normal regions of the coil.

Therciore, no more than three pieces, all of which exceed one complete circle, would be anticipated. Such large pieces would not escape the upper end fitting. If they did, normal core flow would sweep the parts to the OTSG upper head where the piece would be reduced to a size small enough to move through the tubes before reentering the core. Pieces of such size do not cause sufficient flow blockage to be a safety concern.

Preliminary analysis of worse case positioning of broken springs indicates that no configuration will allow sufficient force to prevent CRA insertion or to substantially increase drop time. There is no way for a piece to completely block the CRA path since the fingers are partially inserted in the guide tubes at all times.

The results of the safety analysis indicate that operation with broken HD springs does not affect the health and safety of the public.

Corrective Action: The broken HD springs on the Oconee 2, Batch 7 Fuel Assemblies will be replaced prior to reloading these assemblies in the core. The Oconee 1, Batch 4 fuel assembly is a discharged assembly and no action will be taken for this assembly. The HD springs inspection program, which was initiated at the time of the previous HD spring failures, will continue until future data and inspection results indicate the program is no longer necessary.

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