05000390/FIN-2007007-01
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Finding | |
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| Title | |
| Description | Alternate shutdown capability was provided to cope with a fire in FA 48, the auxiliary instrumentation room containing the RPS cabinets. Alternate shutdown was the chosen coping strategy for this room because it contained all channels of normally used instrumentation circuits and associated panels in close proximity, making it difficult t
protect any one channel. A CO2 suppression system was installed in this room to meet the requirements of Appendix R,Section III.G.3. Design basis documents applicable t the design of the CO2 system were: National Fire Protection Association Standard on Carbon Dioxide Extinguishing Systems, NFPA No.12 - 1973, NRC Supplemental Safety Evaluation Report (SSER) No. 18 (NUREG 0847), and Watts Bar Fire Protection Report (FPR). Review of these documents by the team identified an issue. The SSER states that the CO2 system must achieve a concentration of at least 50 percent within seven minutes of initiation and hold that concentration for 15 minutes. This statement may be construed as meaning the concentration values must be achieved at any point in the room where combustibles capable of deep seated fires are located. The basis for these values in the SSER is testing performed by Sandia National Laboratory on deep seated fires and CO2 systems as described in NRC Information Notice 92-28, Inadequate Fire Suppression System Testing, issued April 8, 1992. The FPR states that the system is capable of achieving 50 percent concentration within seven minutes and maintaining at least a 45 percent concentration for at least 15 minutes. NFPA No.12 - 1973 (the code of record) specifies 50 percent concentration for deep seated fires, but does not specify a definite hold time. The issue is: Given the difference between the SSER and the FPR with regard to the required concentration at the 15 minute point, does the CO2 system meet the design basis? The team reviewed records of a discharge test conducted at the time of initial system installation. The team found that it was a valid test, and that it confirmed the values stated in the FPR with regard to CO2 concentrations. Records showed that a 45 percent concentration was held for 15 minutes measured at 75 percent of room height. Fifty percent concentration for 15 minutes was achieved in the lower half of the room. FA 48 contains a mixture of both thermoset and thermoplastic-type cables. Fire in fire resistant thermoset-type cables could be a deep seated fire. Fire in thermoplastic-type cables would be a surface fire. For the cable trays located in the upper 25 percent of the room, the team did not determine what percentage of these cables were of the thermoset-type. The licensee considered the CO2 system to be functional. Testing demonstrated that 50 percent CO2 concentration for 15 minutes would be achieved in the lower half of the room where the ignition sources in the form of low-voltage, low-power, instrumentation cabinets were located. The possibility of a fire starting in the cabinets spreading to the 8 upper portions of the room along the cables is unlikely because the great majority of the cables are routed in conduits or enclosed raceway as they exit from the tops of the cabinets (i.e. for the first five to seven feet). The only ignition sources in the upper 25 percent of the room would be these thermoplastic cables located in the cable trays. Because the coping strategy for a fire in this fire area is alternative shutdown, none of the cables in this room are used for SSD. Operation of transfer/isolation switches would be necessary to allow the alternative shutdown system to function properly. The licensee initiated Problem Evaluation Report (PER) 125632 to address the issues described in this section. The team concluded that if the fire hazards and the suppression system in FA 48 were properly analyzed, there would be reasonable expectation that such analysis would show the suppression system to be adequate to extinguish any credible fire. In consideration of the above facts and circumstances, an unresolved item (URI) has been established to allow the licensee reasonable time to generate a documented analysis to show that the CO2 system meets the intent of the design basis as stated in the SSER. For a plant licensed to operate after 1979, such an analysis would not have to be submitted to the NRC as a request for approval of modification of License Condition 2F if it does not adversely affect SSD. This issue is identified as URI 05000390/2007007-01, CO2 System in FA 48 Appears to Deviate From Design Criterion in SSER |
| Site: | Watts Bar  |
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| Report | IR 05000390/2007007 Section 1R05 |
| Date counted | Jun 30, 2007 (2007Q2) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.05 |
| Inspectors (proximate) | R Monk R Rodriguez H Gepford L Miller R Aiello M Pribish C Peabody B Caballeron Stapless Walker B Melly P Fillion |
| INPO aspect | |
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Finding - Watts Bar - IR 05000390/2007007 | |||||||||||||||||
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Finding List (Watts Bar) @ 2007Q2
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