ML19263B241
| ML19263B241 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 01/04/1979 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7901150064 | |
| Download: ML19263B241 (2) | |
Text
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1'N5) sACRAMEf4To MufllCIPAL UTILITY DISTRICT O 6201 S Street, Box 15830, Sacrarnento, Cahfornia 95813; (916) 452-3211 January 4, 1979 Director of Nuclear Reactor Regulation Attention:
Mr. Robert W. Reid, Chief Operating Reactors, Branch 4 U. S. Nuclear Regulatory Commission Washington, D. C.
20555 Docket No. 50-312 Rancho Seco Nuclear Generating Station, Unit No. 1
Dear Mr. Reid:
Your letter of November 29, 1978 requested infonnation on containment purging during normal plant operation and the safety features actuation system at Rancho Seco Unit No.1.
The District is providing the following information in response to this request as justification for continuing unlimited purging.
The Rancho Seco Unit No. 1 purge system is described in Section 9.7 of the Final Safety Analysis Report.
The purge system is provided with motor operated isolation valves insida the reactor building and pneumatically operated valves outside the reactar building in both the supply and discharge ducts.
These valves are 6E" butterfly valves, Model No. 60WR, manufactured by the Allis Chalmers Ct mpany.
The valves were designed to seal against the design containment pressures following a LOCA and the butterfly design assures they will close against the dynamic forces of a design basis LOCA.
Allis Chalmers is providing the District verification of this fact.
These valves are normally closed and are operated remotely from the control panel in the control room for the purging operation.
Should a LOCA occur during the purge operation, a safety features actuation signal would initiate valve closure to assure containment isolation.
The safety features actuation system is initiated on high reactor building pressure or low primary system pressure.
These signals are not overriden in order to open the valves.
The radiological consequences of a LOCA occurring during purge operations is discussed in Section 14.3.8.2 of the Final Safety Analysis Report.
This analysis shows that the resulting doses are well below the limits set in 10 CFR 100.
Reactor building purges are conducted for several reasons at Rancho Seco Unit No.1.
On occasion we are confronted with radioactive buildup within the reactor building which would cause gaseous and particulate 79011500
?
AN ELECTRIC sYs1EM S E rVIN G MORE THAh 600,000 IN THE HEART OF C A LIF O R N I A
O Mr. Robert W. Reid January 4,1979 monitoring devices to go off scale.
A purge is therefore required in order to insure that the monitors remain on scale and provide primary system leak detection capabilities based upon radiation.
In addition, reactor building entrances are required by the Technical Specifications for calibration of radiation instrumentation.
In keeping with ALARA, we have always ventilated the building, minimizing exposures to personnel accomplishing this task.
Meeting this single requiremcat requires ventilation in excess of 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br />.
During 1978, there were 1,600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> of purging during plant operation.
If we were to commit to limited purging during plant operation, each purge to satisfy the above requirements would necessitate a plant shutdown and cooldown lasting approximately 4 days.
This, in turn, would result in a
$1.7 million increase in fuel costs to the utility custoners in northern California as a result of burning oil.
Based on the above discussion, the District does not intend to commit to limiting purge operations, even on an interim basis, and will continue unlimited reactor building ptrging unless advised to the contra ry.
Your letter of November 29, 1978 also requested a design review of the safety actuation signal circuits which incorporate a manual override feature to insure that overriding of one safety actuation signal does not also cause the bypass of any other safety actuation signal.
The safety features actuation system incorporated in Rancho Seco Unit No.1 does not incorporate any override or bypass features.
The only time a safety features system may be bypassed is at a primary system pressure below the trip point for the reactor protection system.
This is provided to prevent safety features initiation during a normal plant shutdown and cooldown.
Administrative controls are therefore not required to prevent improper manual defeat of any safety actuation signals.
Sincerely yours, kada J. J. Mattimoe Assistant General Manager and Chief Engineer
.