ML19208B012
| ML19208B012 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 09/04/1979 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7909180420 | |
| Download: ML19208B012 (2) | |
Text
.N esuun SACRAMENTO MUNICIPAL UTILITY DISTRICT C] 6201 s street, Bn 158%, sacramento, California 95813; (915) 452-3211 September 4,1979 Director of Nuclear Reactor Regulation Attention:
Mr. Robert W. Reid, Chief Operating Reactors, Branch No. 4 U. S. Nuclear Regulatory Comission Washington, D. C. 20555 Docket No. 50-312 Rancno Seco Nuclear Generating Station, Unit No. 1
Dear Mr. Reid:
Paragraph 3.1.11(1) of the Fire Protection Safety Evaluation Report attached to License Amendment No.19, dated February 28, 1978 describes the following modification for the east 480 switchgear room:
" Install thermal barriers over all channels A, C, and D conduits containing cables required for safe shutdown."
The District requests that the paragraph be rewritten to state the following:
"Rercute or install a thermal barrier over all channel A, C, and D conduits containing cables whose failure could prevent a safe shutdown and/or cooldown."
This change is necessary to allow the District the option of either rerouting or installing fire barriers on all channel A, C and D conduits containing cables required for safe shutdown and cooldown. The existing paragraph does not give the District the option of rerouting.
Licensing Amendment No.19 requested that design details on the proposed modification in paragraph 3.1.11(1) be submitted to the NRC to assure that the design is acceptable. The design details based on the NRC accepting the District's proposed rewording of the paragraph, are listed below.
Design Details for Implementing Paragraph 3.1.11(1)
The design criteria is to ensure that no function or inriication required for saft shutdown and cooldown is lost or made inoperative for a design basis fire in the east 480 volt switchgear room.
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Mr. Reid September 4, 1979 The east 480 volt switchgear room is a channel "B" room, and a design basis fire in this room will cause the loss of B channel functions.
Therefore the modifications are designed to protect channel A, C and D circuits which are required for safe shutdown and cooldown. This will be accomplished by the following methods:
1.
Insulating channel A monduits that are routed through the room that contains circuits required for safe shutdowc and cooldown. The conduits will be insulated with two inches of fiberfrax hot board manufactured by Carrarundun Company. The insulation will be jacketed with.0lf, inch stainless stees shcets held in place with stainless steel bands.
A description of the qualifying test performed on this insulation system is in the District's Fire Stop Test Report, test set-up one, conduit insulation fire test two.
This test report was submitted to the NRC on March 1, 1978.
2.
Routing required circuits out of the east 480 volt switchgear room through other fire areas. When this is done, a fire hazard analysis will be performed for all the areas that the circuit is routed through to ensure a safe shutdown and cooldown is still possible with a design basis fire in the area with the new circuit.
3.
Reroute the control drive trip circuits that interconnect the Reactor Protection System and control rod drive system in separate conduits. These circuits fail safe, i.e.
cause a reactor trip on an open, short on ground. However.
they were routed in conduits with other circuits and a failure mode existed where the trip circuits could interact with other circuits in the conduit and fail in a non-safe direction. Rerouting the circuit in a separate conduit corrects this problem.
The proposed modification in wording to paragraph 3.1.11(1) and the criteria used to implement the modification ensure that a design basis fire in East 480 volt switchgear room will not prevent safe shutdown and cooldown.
To complete the modification described in paragraph 3.1.11(1) by the end of the 1979-1980 refueling as required by Table 3.1 of the Safety Evaluation Report attached to Amendment No.19, the District requests NRC comments and/or approval on the change in paragraph 3.1.11(1) and the design criteria to implement this change by October 15, 1979.
Sincerely yours, bdA X1ohn Mattimoe Assistant General Manager and Chief Engineer SGL3@