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| Entered date | Event description | |
|---|---|---|
| ENS 45395 | 30 September 2009 15:38:00 | Voluntary notifications, a press release, and a webinar are being made to various government agencies and the media to provide information regarding the installation of temporary structures on top of earthen embankments of the Fort Loudoun, Tellico, Cherokee and Watts Bar dams. These dams are on the Tennessee River System. Recent upgraded flood modeling indicates that there is a possibility for overtopping to occur on these dams during a hypothetical extreme flooding scenario in the winter/spring period. As a precautionary measure, TVA is effectively raising the height of some of the dams in certain areas. These precautionary measures ensure that the TVA nuclear sites (Sequoyah, Watts Bar and Browns Ferry) will remain within their original licensing basis. Currently, Sequoyah Units 1 & 2 (DPR-77 & 79) and Browns Ferry Units 1 & 3 (DPR-33 & DPR-68) are operating at 100% power, Browns Ferry Unit 2 (DPR-52) is in Mode 4. Watts Bar Unit 1 (NPF-90) is shutdown for refueling. The licensee has notified the NRC Resident Inspectors at each of these sites. The licensee's corporate management is issuing a press release. |
| ENS 44814 | 28 January 2009 18:00:00 | 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. |