ML20147D799

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Proposes to Store Seal Plate in Current Position for One Addl Fuel Cycle,Allowing Evaluation of Design Permitting Storage of Seal Plate Rigidly Above Present Location. Discusses Probability of Rupture of Primary Cooling Loop
ML20147D799
Person / Time
Site: Rancho Seco
Issue date: 12/14/1978
From: Mattimoe J
SACRAMENTO MUNICIPAL UTILITY DISTRICT
To: Stello V
Office of Nuclear Reactor Regulation
References
NUDOCS 7812200159
Download: ML20147D799 (1)


Text

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SMUD

. SACRAMENTO MUNictPAL UTILITY DISTRICT O 6201 S Street, Box 15830, Sacramento, California 95813; (916) 452 3211 December 14, 1978 Director of Nuclear Reactor Regulation Attention: Mr. Victor Stello, Jr. , Director Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D. C. 20555

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, Docket No. 50-312 Rancho'Seco Nuclear Gene' rating Station, Unit No.1

Dear Mr. Stello:

Your letter of February 2,1978 requested information regarding the possibility of the Rancho Seco Unit No.1 reactor cavity annulus seal plate and the associated biological shielding becoming missiles in the event of a pipe break inside the reactor vessel cavity. We responded February 21, 1978 and March 17, 1978 stating that the concrete shield plugs are restrained by bolts capable of withstanding the accident pressure transient, but that the seal plate could be lifted following a LOCA.

We further stated that we would remove the seal plate from this position following the present refueling outage.

The District has recently been made aware of a design effort which will allow storage of the plate rigidly above i~ts present location.

We feel this design warrants our evaluation and therefore propose to store the seal plate in its present position for one more fuel cycle. The plate would have to be cut to remove it from present location at this time which' would probably' affect its future sealing capability.

The District still feels that the extremely small probability of a rupture of the primary cooling loop within the reactor cavity coupled with the small probability of the plate being capable of performing any

' significant damage provides justification for operation until the next refueling outage.with the plate stored in its present location. The probability of a pipe rupture within the reactor cavity has been calculated by Science Applications, Incorporated and submitted as topical report SAI-050-77-PA, "An Analysis of the Probability of Pipe Rupture at Various Locations in the -

Primary Loop of a B&W 177 Fuel Assembly PWR".

Sincerely yours ,

' . t . dw/tu J'. J. Mattimoe Assistant General Manager and Chief Engineer 781220015] ,

'AN ELECTRIC SYSILM $ E RVIN G MORE THAN 600,000 IN THE HEART Of cAlliOhHlA

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