ML19269D836
| ML19269D836 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 06/15/1979 |
| From: | Hoffman D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Ziemann D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7906200172 | |
| Download: ML19269D836 (4) | |
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- O General Offices: 212 West Michigan Avenue, Jackson, Michigan 49201 e Area Code S17 7HB-OSSO June 15, 1979 Director, Nuclear Reactor Regulation Att Mr Dennis L Ziemann, Chief Operating Reactors Branch No 2 US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT - FIRE PROTECTION MODIFICATIONS - INFORMATION REGARDING NEED FOR CABLE INSULATION IN RECIRCULATING PUMP ROOM The Fire Protection Safety Evaluation Report accompanying Amendment 25 to License DPR-6 required Consumers Power Company to submit additional information regarding the need for fire protective insulation of certain cables and valve operators in the Big Rock Point recirculating pump room. The possible need for such insulation was raised by NRC letter dated November 20, 1978.
Consumers Power Company letter dated May 30, 1979 stated that this information would be submitted by June 15, 1979. This letter provides the required information.
Consumers Power Company letter dated January 17, 1979 reported our conclusion that insulation of cable and valve operators in the recirculating pump room was not necessary. Further evaluation has reaffirmed that conclusion.
This evaluation included consideration of the functions to be performed by the equipment which would be protected by additional insulation, the magnitude of possible fires in the recirculating pump room and the possible consequences of fires of this magnitude. The size and consequences of possible recirculating pump room fires are discussed in the attachment to this letter.
The November 20, 1978 NRC letter stated that a major purpose of fire protective insulation in the recirculating pump room would be to protect the cabling and valve operators of the emergency condenser system.
Consumers Power Company notes that the emergency candenser is only one of the redundant systems which can be used to safely shut down the plant. The equipment, power supplies, and facilities for each of the redundant systems will be sufficiently separated so that a single fire could not disable more than one system.
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2 Radiation levels in the area of the cable and valve operators which would be insulated are 3 to 4 R/h immediately af ter shutdown and 300 to 400 Mr/h after 6 months.
Insulating these cables and operators and the subsequent complication of maintenance in these areas which would require removing and reinstalling insulation would thus result in additional personnel radiation exposure.
Considering the discussion above and in the attachment regarding the benefits to be gained by insulation, Consumers Power Company does not consider this additional radiation exposure consistent with the philosophy of maintaining exposures as low as reasonably achievable.
Based on the discussion above and ir the attachment, Consumers Power Company does not intend to install fire protective insulation on cable and valve operators in the Big Rock Point recirculating pump room.
David P Hoffman (Signed)
David P Hoffman Assistant Nuclear Licensing Administrator CC JGKeppler, USNRC 2253 217 oc0679-0281a-46
1 c
EVALUATION OF RECIRCULATING PUMP ROOM FIRES The major concern for fire protection in the recirculating pump room, as noted in NRC letter dated November 20, 1978, is a fire involving recirculating pump lubricating oil.
Specifically of concern is whether such a fire would damage cable and valve operators associated with the energency condenser outlet valves or main steam isolation valve.
Other flaa,able materials, such as insulation or recirculating pump motor windings, a re insignificant compared to this lubricating oil. Each of the two pumps cont" ins 31.75 gallons of oil.
The oil has a flash point of approximately 400 F aad an ignition temperature of approximately 600 F+.
The two pumps are separated by about 30 feet.
The cable and valve operators of concern are located approximately 50 feet above the pumps.
The PVC cable has an ignition temperature in excess of 500 F.
The cable is run in steel conduits, thereby providing additional fire protection.
The valve operators and motors have been qualified to a temperature of 245 F.
This qualification involved heating the operators to a uniform temperature of 245 F and operating them continuously.
The operators of concern must operate only once rather than continuously, and it will be shown that the valve operators would not reach a uniform 245 F as a result of a lubricating oil fire.
The recirculating pump room has a free volume of about 100,000 ft3 Average ambient temperature in the room during reactor operation is approximately 150*F.
The room is ventilated such that the air volume is changed out approximately every 3-1/2 minutes (30,000 cfm). The room contains piping, steel grate walkways and ladders, and other equipment.
The walls are concrete and provide a significant heat sink.
Several design features serve to make a lubricating oil fire highly unlikely.
The oil in each pump is contained in closed reservoirs; air is not available in the reservoirs to support combustion.
In addition, the quantity of heat needed to raise the oil in the upper reservoir to its flash point is greater than that which would be released by a fire which completely consumed the insulation in the pu...p motor windings.
Oil which might be spilled or leaked from a reservoir is highly unlikely to ignite since no hot' surfaces, arcs or' other ignition sources are in the area of the pumps, the oil would leak onto the concrete floor which provides a large heat sink to prevent the oil from reachi'.g its flash point, and the oil would flow to an enclosed sump below the pumps which also contains no ignition source.
Despite the factors discussed above, several lubricating oil fires were evaluated to determine their effect.
The fires considered were a 50 fta spill, a 3 gpm spray of oil from a pump, and a 3 gpm leak (other than a spray). These fires were each assumed to completely consume the lubricating oil contained in one pump.
In each case, the amount of oil is sufficient to burn for less than eleven (11) minutes.
The maximum calculated temperature rise, assuming that the ventilation system is the only means of heat removal and all remaining heat is absorbed by room air, is approximately 160 F.
Since ventilation would continue after the postulated fire, this temperature would oc0679-0281a-46
2 immediately begin to fall. Maximum air temperature in the room would thus reach approximately 310*F.
This temperature is below the ignition temperature of the PVC cable (even without considering the protection afforded by the conduit).
This temperature is approximately 65*F higher than the qualification temperature of the valve operators; however, it exists for only a short period. The external surface of the valve operator motor casing could exceed 245 F, but the windings would remain significantly below this temperature.
In addition, the numerous other heat sinks in the room and its walls which were not considered in this analysis would reduce the peak air temperature below 310 F.
It must be noted that the above discussion assumes complete failure of the sprinkler system to operate. The fire suppression system to be installed in this room will include heat detectors and a manually-operated fusible link sprinkler system protecting the pumps and the sump. Any fire would be detected and sound an alarm in the control room. The operator would then operate a switch admitting water to the sprinkler piping.
Use of fusible link sprinkler heads would direct this water onto the area where it is most needed.
The tremendous amount of heat which would be absorbed by this water spray was neglected completely in the analysis discussed above.
In conclusion, insulation of the conduit and valve operators to prevent damage from a one-hour fire is both unnecessary and unwarranted because:
1.
The probability of a fire is small.
2.
Flammable materials other than recirculating pump lubricating oil are inconsequentit1.
3.
The flash point and ignition temperature of the lubricating oil are such that an oil fire is highly unlikely.
4.
Ignition sources are not present in the area of the recirculating pumps or the enclosed sump.
5.
The calculated consequences of a totally unmitigated fire are not sufficient to prevent the valve operators from accomplishing their design function.
6.
The heat which would be absorbed by other equipment and structures would reduce the maximum calculated temperature of the unmitigated fire evaluated, and 7.
A fire suppression system will be provided to control lubricating oil fires in the highly unlikely event that one should occur.
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