ML20044C390
| ML20044C390 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 03/17/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20044C384 | List: |
| References | |
| NUDOCS 9303220401 | |
| Download: ML20044C390 (3) | |
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NUCLEAR REGULATORY COMMISSION i
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- SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO APPENDIX R. 10 CFR PART 50. EXEMPTION TO SECTION III.G CLARIFICATION OF FIRE PROTECTION MODIFICATION OMAHA PUBLIC POWER DISTRICT FORT CALHOUN STATION. UNIT NO. I DOCKET NO. 50-285
1.0 INTRODUCTION
By letter dated August 5,1992, the licensee requested the NRC to clarify the July 1,1986, Safety Evaluation (SE).
Based on interpretation of Omaha Public Power District's (the licensee's) submittal dated April 9,1986, the staff concluded that these cables had been rerouted out of the lower electrical penetration room (Fire Area 34A). The July 1,1986, SE reflects this interpretation and indicates that the area conforms with the requirements of Section III.G of Appendix R.
The staff's interpretation of the licensee's April 9,1986 submittal, as documented in the July 1,1986, SE, is in conflict with the exemption the staff approved for Fire Area 34A in their SE dated July 3, 1985.
By letter dated January 9, 1985, the licensee requested an exemption, pursuant to Sections 50.12(a) and 50.48(c) of 10 CFR, from the requirements of Section III.G.2 of Appendix R.
This exemption requested relief from the requirements that an automatic fire suppression system be installed in Fire Area 34A.
The licensee justified this exemption in their original request on the basis of the limited fire load of the lower electrical penetration room, the j
adequacy of existing fire protection features, and the 1-hour fire barrier they provided for power feeder cables EAl24 (MCC-3A1), EA134 and EA135 (MCC-3B1) and EA140 (MCC-3C1).
The following is the staff's reevaluation of the licensee's request for exemption from the requirements of Section III.G.2 of Appendix R.
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A A 2.0 EVALUATION Existing fire protection features provided for Fire Area 34A include area-wide automatic fire detection, portable fire extinguishers, and manual hose stations.
In addition, this area is bounded by walls, floor, and ceiling of 3-hour fire resistive construction with openings protected by either 3-hour fire-rated doors, dampers, or penetration seals. The combustible materials in Fire Area 34A consist primarily of cable insulation, which represents a fire load of approximately 25,000 British Thermal Units (BTU) per square foot of floor area.
The licensee in their submittal dated January 9,1985, indicated that power feeder cables EAl24 (MCC-3A1), EA134 and EA135 (MCC-3BI), and EA140 (MCC-3C1) would be rerouted in steel conduits to reduce the routing length of these cables in the fire area.
In addition the licensee committed to protect the raceway containing these cables with a 1-hour fire barrier throughout Fire Area 34A. The licensee in their April 9,1986 submittal, as clarified by their August 5,1992 submittal, indicated that the installation of additional conduits inside this fire area to reduce their routing within Fire Area 34A was not required and that an alternative routing for these cables was used. A 1-hour fire barrier has been installed on the raceway (cable air drops, cable trays, and conduits) containing these rerouted power feed cables.
The major fire hazard in this plant area is cable insulation. This insulation is IEEE-383 qualified. Under these conditions, if a fire occurred in this area and involved the cables, it can be expected that the fire would propagate slowly and generate moderate smoke levels during the fire's incipient stage.
Fire Area 34A is completely protected by a smoke detection system. Under these fire and smoke conditions the fire would be promptly detected. Upon detection, it is expected that the appropriate actions would be taken to alert the fire brigade and that the brigade would suppress the fire before fire growth would lead to a rapid heat buildup in the fire area.
Even if fire spread did occur and it did lead to excessive ceiling temperatures in ftre Area 34A, the 1-hour fire barrier would protect safe shutdown related cables until the fire brigade arrived and could control and extinguish tha fire.
Since the fire loading levels in Fire Area 34A would only present a moderate challenge to the 1-hour barrier if the combustibles in fire area room were to become completely involved by fire, the construction of the fire area boundary would confine the effects of the fire to the fire area. Therefore, the presence of a fixed automatic fire suppression system is not necessary to limit the spread of fire. Therefore, the technical basis for this exemption provides reasonable assurance that the existing fire protection features provided for Fire Area 34A, coupled with a prompt response and fire suppression actions by the fire brigade, would protect safe shutdown capability.
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3.0 CONCLUSION
Based on our evaluation, we concluded that the existing fire protection' features provided for Fire Area 34A (lower electrical penetration area),
coupled with the prompt response and fire suppression actions of the plant fire brigade provides an equivalent level of fire safety to that achieved by compliance with Section III.G of Appendix R.
Therefore,- the licensee's basis for requesting an exemption from the fixed automatic fire suppression system requirements, as originally requested in the licensee's January.1,1986, submittal and as clarified by their subsequent April'9, 1986, and August 5, 1992, submittals, remains consistent with our SE dated July 3, 1985, and is acceptable.
Principal Contributor:
P. Madden Date: March 17, 1993 i
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