ML19317G903
| ML19317G903 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 02/21/1978 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Stello V Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8004020561 | |
| Download: ML19317G903 (2) | |
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REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
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DISTRIBUTION FOR INCOMING MATERIAL 50-312 AEC: STELLO V ORG: MATTIMOE J J DOCDATE: 02/21/78 N" O SACRAMENTO MUN UTILITY DISTRIC DATE RCVD: 02/24/7@
DOCTYPE: LETTER NOTARIZED: NO
SUBJECT:
COPIES RECEIVED LTR 1 ENCL O RESPONSE TO NRC"S L DTD 02/02/78.
FURNISHING INFO RE POSSIBILITY OF UNIT 1 REACTOR CoJITY ANNULUS SEAL RING ANDD THE ASSOCIATED GIOLIOGICAL SHIELDING DECOMMING MISSILES IN THE EVENT OF A PIPE EREAK INSIDE THE REACTOR VESSEL CAVITY.
PLANT NAME: RANCHO SECO (SMUD)
REVIEWER INITIAL:
XJM DISTRIBUTOR INITI AL:
oco************** DISTRIBUTION OF THIS MATERIAL IS AS FOLLOWS ******************
GENERAL DISTRIBUTION FOR AFTER ISSUANCE OF OPERATING LICENSE.
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SACRAMENTO MUNICIPAL UTILITY DISTRICT C3 6201 S street, Box l',S30, Sacramento, California 95613; (916) 452-3211 February 21, 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 Docket No. 50-312 Rancho Seco Nuclear Generating.. ",.. '
Station, Unit No.1 Q
Dear Mr. Stello:
k Your letter of February 2,1978 requested information regarding the possibility of the Rancho Seco Unit No.1 reactor cavity annulus seal ring and the associated biological shielding becoming missiles in the event of a pipe break inside the reactor vessel cavity.
The biological shielding installed in the reactor cavity annulus at Rancho Seco Unit.No.1 consists of concrete plugs and, as stated in response to Question 5A.12 of the Final Safety Analysis Report, Page SA-8, these plugs are restrained by bolts capable of withstanding the accident pressure transient.
During plant operation, the seal plate is raised above its sealing position approximately three inches by support bars attached to the plate.
This allows for air circulation out of the reactor cavity through one-half inch gaps between the shield plugs. The District will perform calculations within the next 30 days to determine if the gaps are large enough and the physical characteristics of the seal plate are such that the plate could become a missile capable of affecting the control rod drives.
If such a possibility is determined to exist, modifications will be made which will permit the seal plate to be stored in a safe position.
These modifications would be made during the next refueling outage which should occur during the last quarter of 1978.
The District feels that the extremely small probability of a rupture of the primary cooling loop within the reactor cavity provides justification for continued operation until this outage. This probability has been calculated by Science Applications, Inc., 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, N.#. Mattimoe bO J
Assistant General Manager Nq and Chief Engineer I
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AN ELECTRIC SYSTEM S E RVIN G M O,1 E THAN 600,000 IN THE HEART OF C ALIF0 R N I A