UPDATE 1-Constellation reduces Ginna reactor to half power

(Updates with company comment)

NEW YORK, May 18 (Reuters) - Constellation Energy Group Inc (CEG.N: Quote, Profile, Research) reduced the 498-megawatt Ginna nuclear power station in New York to about half power on Sunday due to irregularities in the circulating water system, a spokesman for the plant said Monday.

He could not say when the unit would return to full power since workers were still looking for the problem.

The circulating water system moves water to the two low pressure turbines.

The Ginna station, which entered service in 1970, is located in Ontario in Wayne County about 20 miles east of Rochester, New York. The U.S. Nuclear Regulatory Commission (NRC) renewed the plant's original 40-year operating license in 2004 for another 20 years until 2029.

One MW powers about 800 homes in New York.

Constellation, headquartered in Baltimore, Maryland, owns and operates about 9,000 MW of generating capacity, markets energy commodities in North America, and transmits and distributes electricity to 1.2 million customers and natural gas to 630,000 customers in Maryland. (Reporting by Scott DiSavino)