A nuclear reactor at Plant Vogtle that operators shut down last week is back in service and sending power to the electric grid, Georgia Power officials reported Wednesday.

Unit 3 at the nuclear plant south of Augusta, which went into full commercial operation last summer, was taken offline July 8 because of a problem with a valve on one of its three main pumps.

Despite the shutdown, Unit 3 has operated at full power more than 96% of the time since it went into service last July 31. By comparison, the average capacity factor for the U.S. nuclear fleet was 93% last year, according to Georgia Power officials.

Unit 3 and its companion – Unit 4, which went into full commercial operation in April – are the first new nuclear reactors built in the United States since the late 1980s.

The project was delayed by seven years, plagued by a series of cost overruns that drove up the final price tag to about $35 billion, more than twice the original estimate of $14 billion.

Opponents of the nuclear expansion at Plant Vogtle urged the Georgia Public Service Commission (PSC) in vain to cancel the project and instead step up the state’s commitment to expanding renewable energy options.

The PSC voted last August to cap the costs Georgia Power would be allowed to pass on to customers at nearly $7.6 billion, with shareholders picking up the rest.

Georgia Power was a 45% partner in the Vogtle expansion, working with Oglethorpe Power, the Municipal Electric Authority of Georgia (MEAG) and Dalton Utilities.

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