UPDATE 1-Dominion Conn. Millstone 2 reactor in cold shutdown

(Updates with company comment)

NEW YORK, July 15 (Reuters) - Dominion Resources Inc (D.N) put the 882-megawatt Unit 2 at the Millstone nuclear power plant in Connecticut into cold shutdown from hot standby mode on July 13 to fix a small leak in the reactor coolant system, a spokesman for the company said Wednesday.

He could not say when the unit would return to service due to competitive reasons.

Electricity traders noted hot standby is one of the modes a reactor moves through on its way to returning to service.

Workers identified the leak in the vicinity of a reactor coolant pump while inspecting systems prior to restarting the unit. It is a small leak of about 0.03 gallons per minute, the company told the U.S. Nuclear Regulatory Commission in a report.

The leak did not pose any threat to plant workers or the public.

The unit had been off line since July 3 due to a grid disturbance caused by offsite lightning strikes to the local electric distribution system.

The 2,037 MW Millstone station is located in Waterford in New London County, about 50 miles southeast of Hartford. There are two reactors at the station, the 882 MW Unit 2 (which entered service in 1975) and the 1,155 MW Unit 3 (1986). The NRC renewed the plant's original 40-year operating licenses in 2005 for another 20 years until 2035 and 2045.

The NRC in August 2008 approved of Dominion's request to up-rate the generating capacity of Unit 3 by about 7 percent to about 1,230 MW. Dominion has said it would implement the up-rate during the fall 2008 refueling outage.