Waterford — Operators at Unit 2 at the Millstone Power Station declared an "unusual event," the lowest of the four levels of emergency classification used by the Nuclear Regulatory Commission, at 9:30 a.m. Sunday but by 11 a.m. had terminated that declaration.

The issue was a leak of greater than 25 gallons per minute from the reactor coolant system, according to Neil Sheehan, spokesman for the NRC. The leakage involving the shutdown cooling system was halted about 10 a.m

The plant's reactor recently shut down for a planned refueling and maintenance outage. The leak is coming from a relief valve on the plant's shutdown cooling system, which has been isolated from the reactor coolant system to allow for repairs, Sheehan said by email.

One of NRC's resident inspectors was at the site to independently evaluate the response to the event and to assess whether there are any equipment challenges, Sheehan said.

Dominion will still need to determine the cause of the leakage and make repairs.