The unit remained offline Sunday while an incident response team explored the cause, Southern Nuclear spokesman Mark Sullivan said.
“We don’t have an exact time when it will be restarted but we expect it will be very soon,” he said, adding that safety systems worked properly and the shutdown was accomplished efficiently and in accordance with site procedures.
The idled reactor is one of two at the site. Unit 2 continues to generate electricity at 100 percent power and was not affected by the outage.
Plant Vogtle, in Burke County, is also undergoing a $14 billion expansion involving the addition of two new Westinghouse AP1000 reactors, scheduled for completion in 2016 and 2017.
The project was licensed in February by the Nuclear Regulatory Commission. About 2,200 workers are involved in the construction.