Waterford — As the Unit 3 reactor at the Millstone Power Station began the restart process on Monday, the Nuclear Regulatory Commission announced a special inspection at the nuclear power plant in response to an unplanned outage of both operating reactors last week and complications that occurred at Unit 3 as it was being shut down.

Millstone spokesman Ken Holt said Monday that testing was being done as Unit 3 began the restart process and the return to full power production over the next few days. Unit 2, the smaller, older of the two operating reactors at the site, was restarted Wednesday and returned to full production Thursday.

Holt said a five-member inspection team from the NRC arrived Monday morning and is expected to spend at least a week investigating the shutdowns of the two reactors May 25.

“Their focus will primarily be on Unit 3,” he said. “We will provide them with any information they need to make sure a full inspection is conducted.”

NRC spokesman Neil Sheehan said inspectors will examine the circumstances of the shutdowns but will focus especially on three Unit 3 areas: a pressurized tank for cooling water that ruptured; and the overflows of another tank and of a turbine-driven auxiliary feedwater pump. The pump, part of reactor safety systems, already is the subject of a special inspection that began Feb. 3 after repeated problems. A final report has not yet been released.

The team that arrived Monday is expected to issue a report within 45 days of the inspection, Sheehan said, adding that it is too soon to say whether penalties or fines are possible.

In a news release, the NRC said the inspection would cover the effectiveness of Millstone owner Dominion’s response to the event, equipment performance and the company’s evaluations of what occurred.

“There were developments during the course of the reactor shutdowns that would not be expected and that therefore merit a closer look, with a particular attention on what happened at Millstone Unit 3,” NRC Region I Administrator Bill Dean said.

The shutdown occurred just after 7 a.m. May 25 due to a loss of power off-site. Nuclear plants don’t only send power out to the grid. They also take power from it for operations. The units safely shut down and there were no effects on plant workers or public health and safety, the NRC said. The cause of the power loss subsequently was determined to have been an electrical fault that interrupted the flow of energy from a high-voltage power line, one of three off-site lines feeding Millstone.

An “unusual event” — the lowest of four levels of emergency classifications used by the NRC — was declared by Millstone at 7:15 a.m. The declaration was terminated at 2:14 p.m. after the restoration of power, which occurred at 12:56 p.m.

Millstone Unit 2 did not experience any significant complications as it was shutting down. However, several complications occurred at Millstone Unit 3, the NRC said.

j.benson@theday.com