ENS 44814
ENS Event | |
|---|---|
19:25 Jan 28, 2009 | |
| Title | Unanalyzed Condition Related to a Postulated Appendix R Fire Scenario |
| Event Description | A postulated Appendix R fire scenario has been identified which could result in the plant being in an unanalyzed condition that may degrade plant safety. The unanalyzed condition involves a potential loss of power to the credited train of fire safe shutdown equipment for postulated fires in two areas of the Auxiliary Building.
Safety-related loads on the 6.9KV Shutdown Boards (Centrifugal Charging Pumps, Safety Injection Pumps, Containment Spray Pumps, Motor-Driven Auxiliary Feedwater Pumps, and Residual Heat Removal Pumps) are equipped with local control switches to allow starting or stopping the pumps from the Auxiliary Building. The DC control circuit wiring for these local switches is routed in the same area as the power cables for pump motors. If the fire damages the control circuit cables, the control circuit fuses may fail, resulting in loss of trip capability for the associated 6.9KV breaker. If the breaker is already closed (due to a spurious signal or a previous valid start signal), then the breaker could be disabled in the closed position. If the fire damages the power cables resulting in a phase-to-phase fault with the load breaker trip capability disabled, then the Shutdown Board feeder breaker is designed to trip open on overcurrent to provide backup protection. This could result in the shutdown board being de-energized. In two areas in the Auxiliary Building (elevation 669 and 690 common areas), the above scenario could result in a condition which is outside the fire safe shutdown analysis due to loss of power to the credited train of fire safe shutdown equipment (e.g. Centrifugal Charging Pump, Essential Raw Cooling Water Pump, and motor-operated valves). As a result of this condition, Sequoyah has entered the Fire Protection Report Limiting Condition for Operation 3.7.12 for inoperable fire barriers. In accordance with this LCO action, the operability of fire detectors in the affected areas has been verified and an hourly fire watch has been established in the affected areas. This issue has been entered into the corrective action program. A permanent resolution is being evaluated. The NRC Resident Inspector has been notified. |
| Where | |
|---|---|
Sequoyah  Tennessee (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+-1.42 h-0.0592 days <br />-0.00845 weeks <br />-0.00195 months <br />) | |
| Opened: | Mike Brubaker 18:00 Jan 28, 2009 |
| NRC Officer: | Bill Huffman |
| Last Updated: | Jan 28, 2009 |
| 44814 - NRC Website | |
Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 544872020-01-22T03:18:00022 January 2020 03:18:00
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