Two nuclear plants ended outages as the Monticello plant in Minnesota restarted following a reactor trip and Georgia’s Hatch 2 reactor completed a maintenance project.
At Monticello, northwest of Minneapolis, full power came back online Monday morning. The General Electric type-3 boiling water reactor shut down automatically on Oct. 21 following the lockout of an auxiliary power transformer, according to a Nuclear Regulatory Commission event report. Xcel Energy later reported a cable failure caused the transformer problem, interrupting power to part of the site.
Two emergency diesel generators started automatically, but the NRC report indicated “the 11 ESW [emergency service water] pump (cooling for the #11 emergency diesel) failed to develop required pressure.” The report said the generator ended up tagged as out of service.
The plant’s safety systems functioned as designed, but the event also prompted operators to notify state regulators after exceeding rules on the temperature rate of change at the reactor’s discharge canal.
Unit 2 at Southern Co.’s Hatch plant near Baxley, Ga., resumed electrical generation on Saturday. The GE type-4 BWR was down for seven days while workers replaced a relief valve inside the dry well of its containment, according to a company release.