ML19309B027
| ML19309B027 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 03/17/1978 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Stello V Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8004020504 | |
| Download: ML19309B027 (3) | |
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REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
DISTRIf8UTION FOR INCOMING MATERIAL 50-S17 REC: STELLO V ORG; MATTIi10E J J DOCDATE: 03/17/78 NRC SACRAMENTO MUN UTIL DIST DATE RCVD: 03/22/78 DOCTYFE. LETTER NOTARI ZED: NO COPIES RECEIVED
SUBJECT:
LTR 1 ENCL 40 REEFON9E TO NRC LTR DTD 02/02/78.
FURNISHING INFO PE POSSIELITY OF UNIT 1 hEACTOR CAVITY ANNULUF SEAL FLATE AND THE ASSOCIATED BIOLOGICAL SHIELDING EECGilIl4G MISSILES Iii THE EVENT OF A PIFE EREAK INSIDE THE REACTOR VESSEL CAVITY.
FLANT NAME. RANCHO SECO (SMUD)
REVIEWER INITIAL:
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L SACRAMENTO MUNICIPAL UTILITY DISTRICT O 6201 s street, Box 15830, Sacramento, Califomia 95813; (916) 452-3211 March 17, 1978 i
Director of Nuclear Reactor Regulation T
M(Q* /D Attention:
Mr. Victor Stello, Jr., Director Y
Division of Operating Reactors D
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Docket No. 50-312 Rancho Seco Nuclear Generating f
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 stating that the concrete shield plugs are restrained by bolts capable of withstanding the accident pressure transient. We also committed to perfonn an analysis to determine if the seal plate could become a missile and submit the results of this analysis to you within 30 days.
As we stated in our previous letter, the seal plate is stored approximately 3" above its sealing position by support bars attached to the plate during plar.t operation. This leaves a gap for pressure relief which lowers the force acting upward on the plata. However, our analysis of the seal plate shows that the pressure differential across the seal plate resulting from pressures generated within the reactor cavity follow-ing a LOCA could lift the plate.
It is impossible to determine the extent of lifting because the plate would rotate and be restrained fmn further upward motion due to interference from the reactor vessel head insulation.
As a result of this determination, the District proposes to store the seal plate in a position which will eliminate the possibility of it becoming a missile following the next refueling outage.
Several possibili-ties exist which will have to be evaluated, such as restraining the plate l
in its present position, storing the plate at a higher elevation, or cutting l
the plate in half so that it can be removed from around the reactor vessel head during plant operation.
The District 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 signifi-cant damage provides justification for continued operation until the next M
,f A00I f S ll1o AN ELECTRIC SYSTEM s E RVIN G MORE THAN 600.000 IN THE HEART OF C ALIF0 R N I A
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Mr. Victor Stello, Jr. March' 17,1978
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refueling outage. 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,
. 'b h M
t J. 'J. Mattimoe Assistant General Manager and Chief Engineer 9
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