ENS 42243
ENS Event | |
|---|---|
15:30 Jan 5, 2006 | |
| Title | Unanalyzed Condition Involving Rcic Operation During Mcr Evacuation |
| Event Description | During an engineering assessment, a condition was found which does not meet the assumptions of the River Bend post-fire safe shutdown analysis. 10CFR50 Appendix R states that for alternate shutdown capability (i.e. shutdown from outside the main control room), reactor coolant system process variables shall be maintained within those predicted for a loss of normal AC power, and the fission product boundary integrity shall not be affected. Generic Letter (GL) 86-10, 'Implementation of Fire Protection Requirements,' states that the following assumptions are required for evaluation of a control room fire: 1) fire-induced spurious operation of safe shutdown components has occurred; 2) offsite power is lost; and, 3) the emergency diesel generators (DGs) do not automatically start.
Based on the conservative assumptions imposed by GL 86-10, the following control room fire scenario must be addressed. A fire is assumed to cause motor-operated valve E51-MOVF063, the inboard steam supply to Reactor Core Isolation Cooling (RCIC) turbine to close. The same fire requires the main control room (MCR) to be evacuated, and during relocation to the Division 1 Remote Shutdown panel, offsite power is lost. The post-fire safe shutdown analysis has evaluated RCIC to be available from the Remote Shutdown Panel in order to maintain reactor water level, and that the Division 1 and 3 DGs are started locally. The Division 2 DG is not analyzed to remain free of damage caused by the MCR fire. Since valve E51-MOVF063 is powered from Division 2, and there is no Division 2 power available to re-open the valve, steam would not be available to power the RCIC turbine. E51-MOVF063 is located in the drywell, making manual operation of the valve impractical. Therefore, RCIC is postulated to not be available to maintain reactor level. Establishing reactor level control is a time-critical function that is required to occur within ten minutes of MCR evacuation in order to meet one of the Appendix R safe shutdown performance goals. This condition involves compliance with 10CFR50, Appendix R. Plant equipment remains operable. The scope of this analysis deficiency is limited to the MCR fire scenario, with three concurrent failures. The MCR Is continuously manned. The affected cables in the MCR under-floor area are protected by fire detection and automatic suppression systems, which would rapidly detect and smother a fire. Introduction of ignition sources, such as work involving welding or grinding, is strictly controlled by station procedures. While the assumptions of the post-fire safe shutdown analysis are not met for this scenario, it has been verified that the components required to properly align the Division 1 Residual Heat Removal system in the low pressure coolant injection mode would be available at the Division 1 Remote Shutdown Panel. Control of three safety-relief valves is also available at the Division 1 Remote Shutdown Panel to depressurize the reactor vessel for low pressure injection. An analysis is under way to determine the response of reactor water level, given these conditions. The licensee notified the NRC Resident Inspector. |
| Where | |
|---|---|
River Bend  Louisiana (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+0.23 h0.00958 days <br />0.00137 weeks <br />3.15054e-4 months <br />) | |
| Opened: | Glenn Krause 15:44 Jan 5, 2006 |
| NRC Officer: | Jeff Rotton |
| Last Updated: | Jan 5, 2006 |
| 42243 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |