Arizona Public Service's 1,406-MW Palo Verde-2 nuclear reactor in Wintersburg, Arizona, remained shut Thursday automatically tripping at 11:28 am MDT (1728 GMT) Wednesday after a control rod dropped into the core during testing, company spokesman Alan Bunnell said.
"No major equipment was inoperable prior to the event that contributed to the event. The cause of the reactor trip is under investigation," said an event report filed with the US Nuclear Regulatory Commission.
"The event did not adversely affect the safe operation of the plant or the health and safety of the public," the report added.
Bunnell said the unit is expected to connect to the grid and return to 100% of capacity over the Memorial Day weekend.
The unit was operating at 100% of capacity early Wednesday, the NRC said in a daily reactor status report.
The adjacent 1,402-MW Palo Verde-1 and 1,405-MW Palo Verde-3 reactors were each operating at 100% of capacity early Thursday, according to the NRC.
