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While restoring power to the 3C 480V Load … While restoring power to the 3C 480V Load Center following planned maintenance, the 3A safety related 4KV Bus was deenergized by the 3A Sequencer. This resulted in a valid actuation of the emergency diesel generator. The plant was in Mode 5, depressurized, with reactor coolant system level at approximately the vessel flange level. This resulted in a temporary loss of residual heat removal flow which was restored within approximately seven (7) minutes. Reactor coolant system temperature increased from 113 degrees F to 140 degrees F.</br>Reactor coolant system level and temperature were stabilized at pre-event values.</br>At this time the licensee is preparing to restore off-site power to the 3A Bus and put the emergency diesel generator in standby. The licensee is also investigating the cause of the power loss to the 3A safety related 4KV Bus.</br>The licensee will notify the NRC Resident Inspector.</br>* * * UPDATE FROM G. RICHARDSON TO M. RIPLEY 2248 EST 03/09/06 * * *</br>In response to questions regarding the cause of the loss of the 3A 4KV bus, the following information is provided: </br>The 3C 480 volt Load Center was de-energized for maintenance and was being restored at the time of the event. One of the maintenance activities associated with the 3C Load Center involved replacement of the 480V feeder breaker for the load center. A rotating cam inside the auxiliary switch for the replacement breaker was misaligned. The misaligned cam caused the switch contacts to operate in reverse, such that normally open contacts would be normally closed and vice versa. One of the auxiliary contacts on the 3C Load Center 480V feeder breaker provides input to the A-train Emergency Diesel Generator (EDG) Load Sequencer. With this contact operation reversed (closed vs. open with the breaker open), the Load Sequencer sensed undervoltage on the 3C Load Center, when the 4kV feeder breaker for the load center was closed. The contact being open would normally block the undervoltage signal, until the 480V feeder breaker was closed and the bus was energized. Once the A-train Load Sequencer sensed the undervoltage condition, the 3A 4kV bus was stripped and then re-energized from the 3A EDG.</br>The licensee notified the NRC Resident Inspector. Notified R2DO (Fredrickson)nt Inspector. Notified R2DO (Fredrickson)
20:53:00, 8 March 2006 +
22:38:00, 8 March 2006 +
20:53:00, 8 March 2006 +
While restoring power to the 3C 480V Load … While restoring power to the 3C 480V Load Center following planned maintenance, the 3A safety related 4KV Bus was deenergized by the 3A Sequencer. This resulted in a valid actuation of the emergency diesel generator. The plant was in Mode 5, depressurized, with reactor coolant system level at approximately the vessel flange level. This resulted in a temporary loss of residual heat removal flow which was restored within approximately seven (7) minutes. Reactor coolant system temperature increased from 113 degrees F to 140 degrees F.</br>Reactor coolant system level and temperature were stabilized at pre-event values.</br>At this time the licensee is preparing to restore off-site power to the 3A Bus and put the emergency diesel generator in standby. The licensee is also investigating the cause of the power loss to the 3A safety related 4KV Bus.</br>The licensee will notify the NRC Resident Inspector.</br>* * * UPDATE FROM G. RICHARDSON TO M. RIPLEY 2248 EST 03/09/06 * * *</br>In response to questions regarding the cause of the loss of the 3A 4KV bus, the following information is provided: </br>The 3C 480 volt Load Center was de-energized for maintenance and was being restored at the time of the event. One of the maintenance activities associated with the 3C Load Center involved replacement of the 480V feeder breaker for the load center. A rotating cam inside the auxiliary switch for the replacement breaker was misaligned. The misaligned cam caused the switch contacts to operate in reverse, such that normally open contacts would be normally closed and vice versa. One of the auxiliary contacts on the 3C Load Center 480V feeder breaker provides input to the A-train Emergency Diesel Generator (EDG) Load Sequencer. With this contact operation reversed (closed vs. open with the breaker open), the Load Sequencer sensed undervoltage on the 3C Load Center, when the 4kV feeder breaker for the load center was closed. The contact being open would normally block the undervoltage signal, until the 480V feeder breaker was closed and the bus was energized. Once the A-train Load Sequencer sensed the undervoltage condition, the 3A 4kV bus was stripped and then re-energized from the 3A EDG.</br>The licensee notified the NRC Resident Inspector. Notified R2DO (Fredrickson)nt Inspector. Notified R2DO (Fredrickson)
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00:00:00, 9 March 2006 +
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