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| Entered date | Event description | |
|---|---|---|
| ENS 47510 | 8 December 2011 13:30:00 | During Operating Experience (OPEX) review of Browns Ferry Fire Protection ENS 47374, 'Deficiency Identified in Transition to Performance Based Standard for Fire Protection,' a similar condition was identified at Clinton Power Station. During site review, it was determined that original plant wiring design for the station battery ammeter contains a 'shunt' in the current flow from each direct current (DC) battery. Bolted on the shunt bar are two IEEE 383 qualified leads to a current meter in the main control room (MCR). The small difference in voltage between the two taps on the shunt is enough to deflect the current gauge in the MCR when current flows from the battery through the shunt. The ammeter wiring attached to the shunt does not have fuses, and if one of these ammeter wires shorts to ground at the same time another DC wire from the opposite polarity on the same battery also shorts to ground, a ground loop through the unfused ammeter cable could occur. With enough current going through the cable, the potential exists that a fire in the raceway system or MCR could occur wherever the cable is routed. This design condition exists in Divisions 1, 2, 3, and 4. This condition is reportable in accordance with 10CFR50.72(b)(3)(ii)(B), 'Any event or condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety.' Compensatory fire watch measures have been implemented for affected areas of the plant. The NRC Resident Inspector has been notified. |