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On April 23, 2008, at 3:56 p.m. CDT, power … On April 23, 2008, at 3:56 p.m. CDT, power was lost on the reactor protection system (RPS) bus 'B'. The plant was operating at 100 percent power at the time. The loss of RPS bus 'B' interrupted power to the containment isolation actuation circuitry. This caused the Division 2 containment isolation valves in various balance-of-plant systems to automatically close, as designed. Plant operators implemented recovery procedures to shift RPS 'B' to its alternate power supply, and restore the systems affected by the isolation to service. The containment isolation valves were confirmed to have actuated as required. Plant (generating) capacity was not interrupted by the containment isolation signal.</br>The investigation of this event did not conclusively determine the cause of the loss of RPS bus 'B'. At the time of the event, scheduled maintenance was in progress to replace a relay which had contacts in the RPS 'B' circuitry. It is postulated that during this work, the technician inadvertently contacted part of the relay case while re-terminating the wiring, causing a short-circuit which blew a fuse in the circuit. This caused the output breaker on the RPS 'B' motor-generator set to trip, which de-energized the bus.</br>This event is being reported in accordance with 10CFR50.73(a)(2)(iv)(A) as an invalid actuation of the Division 2 containment isolation actuation system.</br>The loss of RPS 'B' also caused a half-scram signal to be generated.</br>The licensee has notified the NRC Resident Inspector.e has notified the NRC Resident Inspector. +
20:56:00, 23 April 2008 +
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13:27:00, 9 June 2008 +
20:56:00, 23 April 2008 +
On April 23, 2008, at 3:56 p.m. CDT, power … On April 23, 2008, at 3:56 p.m. CDT, power was lost on the reactor protection system (RPS) bus 'B'. The plant was operating at 100 percent power at the time. The loss of RPS bus 'B' interrupted power to the containment isolation actuation circuitry. This caused the Division 2 containment isolation valves in various balance-of-plant systems to automatically close, as designed. Plant operators implemented recovery procedures to shift RPS 'B' to its alternate power supply, and restore the systems affected by the isolation to service. The containment isolation valves were confirmed to have actuated as required. Plant (generating) capacity was not interrupted by the containment isolation signal.</br>The investigation of this event did not conclusively determine the cause of the loss of RPS bus 'B'. At the time of the event, scheduled maintenance was in progress to replace a relay which had contacts in the RPS 'B' circuitry. It is postulated that during this work, the technician inadvertently contacted part of the relay case while re-terminating the wiring, causing a short-circuit which blew a fuse in the circuit. This caused the output breaker on the RPS 'B' motor-generator set to trip, which de-energized the bus.</br>This event is being reported in accordance with 10CFR50.73(a)(2)(iv)(A) as an invalid actuation of the Division 2 containment isolation actuation system.</br>The loss of RPS 'B' also caused a half-scram signal to be generated.</br>The licensee has notified the NRC Resident Inspector.e has notified the NRC Resident Inspector. +
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46.688 d (1,120.52 hours, 6.67 weeks, 1.535 months) +
20:56:00, 23 April 2008 +
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