The Nuclear Regulatory Commission (NRC) will begin a special inspection on the unplanned shut down of the unit 2 reactor on 15 November at Progress Energy’s Brunswick nuclear power plant in the US state of North Carolina.
The NRC said the unit 2 was restarting after a maintenance outage when operators identified unacceptable reactor coolant system leakage.
The unit, which had reached 7% power, was manually scrammed.
The leak rate slowed as the pressure was decreased and the unusual eEvent was terminated after about five hours.
During preliminary leak investigation activities, plant employees determined that the reactor pressure vessel head had not been fully tensioned, the NRC said.
The NRC's resident inspectors at Brunswick immediately began assessing the incident, and are continuing to monitor the licensee's activities.
The on-site portion of the inspection will take several days.