On September 29, 2006, at 1:33 pm
CDT, a safety-related 120VAC distribution panel was inadvertently de-energized during a planned shift of its power supply. The plant was operating at 100 percent power at the time. The loss of power resulted in the automatic closure of
primary containment isolation valves in the
reactor water cleanup and the suppression pool cooling/cleanup systems. This event is being reported in accordance with
10CFR50.73(a)(1) as an invalid actuation of the containment isolation valves affecting more than one system.
This event occurred during a planned shift of the inverters that supply the distribution panel. This shift was being performed to support post-maintenance testing of one of the inverters. The operators performing the shift were utilizing the appropriate procedure. At a certain point in the procedure, the off-going inverter was deenergized, and the operators discussed the expected equipment response. Following that discussion, a step was erroneously performed out of sequence, resulting in the loss of power to the 120VAC distribution panel. The primary containment isolation signal was actuated as designed, and the appropriate valves responded correctly.
Reactor power was not affected by the containment isolation signal. The pertinent response procedures were implemented, and actions were taken to restore the distribution panel to service. This was completed at 5:31 pm CDT that day.
The licensee will notify the NRC Resident Inspector.
