ENS 43379
ENS Event | |
|---|---|
17:31 May 21, 2007 | |
| Title | Potential Division 1 Edg Damage Due to Loss of Service Water Cooling During Control Room Fire |
| Event Description | During a review of an Operating Experience issue (LO-GLO-2006-0090 CA5), a condition was found which is not consistent with 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) support systems (service water cooling) for critical post-fire safe shutdown components must remain free from fire damage. Generic Letter 86-10, 'Implementation of Fire Protection Requirements' state 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) loss of automatic starting of the onsite AC generators as well as the automatic function of valves and pumps whose circuits could be affected by a control room fire.
In addition to loss of automatic start of the emergency diesel generators, the post-fire safe shutdown analysis must also evaluate the consequences if the diesel generators do start concurrent with fire induced multiple spurious actuations. Since control circuits for motor operated valves for the standby service water system are routed in the control room, fire induced shorts could place these valves in a position that would prevent service water from cooling the Division 1 emergency diesel generator. In the time required for Operations personnel to evacuate the control room and re-establish control of the standby service water system at the Division 1 Remote Shutdown panel, thermal damage to the diesel generators could render the Division 1 generator incapable from performing its post-fire function. The RBS [River Bend Station] post-fire safe shutdown analysis is based on the assumption that the diesel generator high temperature trip function would remain functional based on the fact that the trip logic is located outside of the main control room and therefore would remain free from fire damage. The investigation performed during the OE review uncovered the fact that at RBS when the emergency diesel generator is started in the emergency mode the non-safety trips (such as high temperature) are by-passed. The loss of off-site power starts the diesel generator in the emergency mode; therefore the high temperature trip is by-passed. With the non-safety trips by-passed, the diesel generator will continue to run even without sufficient cooling. This condition involves compliance with 10CFR50, Appendix R. Plant equipment remains capable of performing the remaining design functions. The scope of this analysis deficiency is limited to the Main Control room fire scenario, with multiple concurrent failures. The Control Room is continuously manned. The affected cables in the MCR under-floor area are protected by automatic 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. Furthermore Standing Order #193 Revision 3 limits hot work in the main control room during Modes 1,2 and 3. 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:+1.77 h0.0738 days <br />0.0105 weeks <br />0.00242 months <br />) | |
| Opened: | Vern Carlson 19:17 May 21, 2007 |
| NRC Officer: | Jeff Rotton |
| Last Updated: | May 21, 2007 |
| 43379 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |