The Ginna nuclear power plant in Wayne County, NY, returned to full service Monday morning, four-and-a-half days after going off line.
The plant suffered an unplanned shutdown when its generator went down. That caused control rods to automatically insert into the reactor, halting the nuclear reaction.
The problem with the generator was with an incorrectly set protective electrical relay, officials said.
Workers wrapped up repairs Sunday morning, said Maria Hudson, a spokeswoman for plant owner Constellation Energy Nuclear Group. Power production gradually ramped up and reached 100 percent of capacity about 3 a.m. Monday, she said.
Workers disabled the troublesome relay so it will not mistakenly shut down the reactor, said Neil Sheehan, a spokesman for the U.S. Nuclear Regulatory Commission (NRC).
Workers will repair or replace the relay during the next refueling and maintenance outage. Nuclear plants undergo these routine outages every 18 months; the last one at Ginna was in the fall of 2012.
“The NRC has no safety concerns with the company’s actions to address the problem or with the restart,” Sheehan said Monday.
Rochester Gas and Electric Corp., which has an agreement under which it can purchase most of Ginna’s output, had been buying replacement power in the New York energy market.