05000458/LER-2006-001
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 01-5-2006 |
|---|---|
| Report date: | 03-06-2006 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4582006001R00 - NRC Website | |
Establishing reactor water level control is a time-critical function required to occur within ten minutes of a main control room evacuation in order to meet the Appendix R safe shutdown performance goal of maintaining reactor coolant inventory to prevent core damage.
Until this condition is resolved, interim compensatory actions have been taken.
Abnormal Operating Procedure (AOP)-0031, "Shutdown From Outside the Main Control Room" has been revised to add an action that, upon confirmation of an MCR fire, an operator will be dispatched to open the circuit breaker which powers E51-MOVF063. The intent of this action is to remove power from the valve before it can spuriously close.
The required safe shutdown position for the valve is open. Establishing this action as a compensatory measure is consistent with the guidance provided in Regulatory Issue Summary (RIS) 2005-07, "Compensatory Measures to Satisfy the Fire Protection Program Requirements." Also, a prohibition on hot work within the MCR has been put in place pending the resolution of this issue.
CAUSAL ANALYSIS
Development of the original post-fire safe shutdown analysis methodology assumed that, for each fire area, each and every spurious actuation would occur individually. The analysis evaluated each potential fire induced spurious actuation, and identified the single worst case situation. After having selected the worst case spurious actuation, the analysis developed a mitigating action to overcome the malfunction of the fire damaged component. In the case of the MCR fire, RBS determined that a stuck-open reactor safety-relief valve (SRV) was the single worst case spurious actuation. The basis for deciding on a stuck-open SRV as the worst case spurious was the potential for uncovering the reactor core and damaging the fuel cladding. Using the stuck open SRV assumption, it was calculated that the operators had approximately ten minutes to align the RCIC system at the Division 1 remote shutdown panel in order to keep reactor water level above the top of active fuel. Without the stuck-open SRV, the minimum time needed to start the RCIC system is significantly greater than the ten minutes calculated.
A loss of offsite power and the failure of the Division 2 DG were also assumed during the MCR fire. No concurrent spurious actions in addition to the open SRV were assumed.
When RIS 2004-03, "Risk-informed Approach for Post-fire Safe Shutdown Associated Circuit Inspections," was issued, it provided clarification of the position that multiple, simultaneous spurious actuations are to be included during implementation of the post- fire safe shutdown analysis. It was during the development of the RBS response to RIS 2004-03 that the reported condition was discovered.