On January 15, 2005, at 2:12 a.m.
CST, while the plant was operating at 100 percent power, a
manual reactor scram was initiated. This action was procedurally required in response to an alarm received at 2:10 a.m. which indicated a ground fault in the main generator. The plant shutdown proceeded normally, and safety systems responded as required. This event is being reported in accordance with
10CFR50.73(A)(2)(iv)(a) as a condition that required the manual actuation of the
reactor protection system.
Reactor water level was adequately controlled by the main
feedwater system. No actuations of
emergency core cooling systems, reactor
safety relief valves, or standby diesel generators were required. The ground fault alarm relay was found to be overly sensitive to a low ground current, causing it to actuate early. Absent an intrusive internal examination of the generator, the most likely cause of the ground leakage current is deposition of
copper oxide in the
rectifier banks. These deposits resulted from an abnormally low dissolved
oxygen concentration in the
stator water cooling system due to a small
hydrogen leak into the system. There were no safety systems out of service at the time of the event. This event was of minimal safety significance.