|UNANALYZED CONDITIONS DISCOVERED DURING NFPA 805 TRANSITION REVIEW |
During the licensee's NFPA 805 transition review process, several unanalyzed conditions were discovered but determined to be not reportable at that time. During subsequent review, the licensee determined these conditions did meet reporting requirements.
The following unanalyzed conditions affect all three Browns Ferry units:
"On 5/11/2010, it was determined that in the event of an Appendix-R fire, multiple hot shorts affecting reactor pressure instrument loops, Safety Relief Valves (SRV) overpressure logic or ADS [Automatic Depressurization System] logic could cause 2 to 13 SRVs to spuriously open, for certain fire areas. The current Appendix R safe shutdown analysis only assumes 2 SRVs spuriously open. The issue has significant safety impact due to the potential for one fire scenario to result in spurious opening of multiple SRVs, loss of low pressure inventory makeup, and loss of the condensate system for inventory makeup, which would challenge adequate core cooling during performance of Safe Shutdown Instructions.
"On 8/18/2010, it was determined that in the event of an Appendix-R fire, fire induced circuit damage can potentially result in the inability to manually close the following Motor Operated Valves: Residual Heat Removal Heat Exchanger outlet valves and Emergency Equipment Cooling Water pump cross-tie valves. The failure to be able to manually close these valves could result in the loss of decay heat removal function and loss of credited diesel generators to power required safe shutdown equipment. These issues have significant safety impact since the capability to manually close these valves is necessary to ensure adequate core cooling during performance of BFN Safe Shutdown Instructions.
"On 9/30/2010, it was determined that in the event of an Appendix-R fire, fire induced multiple hot shorts could cause both Inboard and Outboard RHR test return valves, and Drywell Spray and Suppression Pool Spray valves to spuriously open due to damage to the valve control circuit cables. This could result in draining of the Pressure Suppression Chamber Head Tank and the affected low pressure Emergency Core Cooling System loop piping (RHR or CS). Consequently, the discharge pipe in the credited Residual Heat Removal (RHR) loop may not be filled and vented when the Safe Shutdown Instructions (SSIs) call for the RHR pump to be started. The resulting water hammer could result in piping system damage resulting in loss of core cooling and decay heat removal functions and loss of suppression pool inventory. Additionally, single spurious actuation of Core Spray (CS) test return valves due to fire damage to their control circuits could have the same results. These issues have significant safety impact since they would challenge the ability to provide adequate core cooling during performance of Safe Shutdown Instructions.
On 8/22/2011, two unanalyzed conditions were discovered:
First, "it was determined that, in the event of an Appendix-R fire in certain areas, fault propagation due to loss of the breaker control circuit in conjunction with power cable damage could result in de-energization of the associated 4kV Shutdown Board. This potential exists since some 4kV Shutdown Board load breakers are not equipped with separate fuses for trip circuits extending beyond the board. This condition could result in a loss power to credited safe shutdown equipment that would challenge the ability to provide adequate core cooling during performance of BFN Safe Shut down Instructions.
Second, "it was determined that in the event of an Appendix-R fire in certain areas, Multiple Spurious Operations (MSO) could result in the Main Steam Isolation Valves failing to close, or to re-open. This potentially results in a challenge to control inventory loss during performance of Safe Shut down Instructions.
The following unanalyzed condition only affects Unit 2:
"On 8/18/2010, it was determined that in the event of an Appendix-R fire, fire induced circuit damage can potentially result in the inability to manually close certain Main Steam Drain Line Motor Operated Valves. The current Appendix R safe shutdown analysis credits manual closure of these valves. Failure to close these valves results in loss of suppression pool inventory which could challenge adequate core cooling during performance of BFN Safe Shutdown Instructions."
Compensatory actions in the form of fire watches to mitigate all these conditions are in place in accordance with the BFNP Fire Protection Report. The licensee will make the required 60-day written reports in accordance with 10CFR50.73(a)(2)(ii)(B). These events were entered into the licensee's Corrective Action Program.
The licensee has notified the NRC Resident Inspector.