UPDATE 1-Constellation N.Y. Ginna reactor reduced

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NEW YORK, May 16 (Reuters) - Constellation Energy Group Inc's (CEG.N: Quote, Profile, Research, Stock Buzz) 498-megawatt Ginna nuclear power station in New York was operating at 50 percent of capacity early Friday, the U.S. Nuclear Regulatory Commission said in a report.

A company spokesman said a level control malfunctioned, causing a heater drain pump to shut down. The unit was reduced to 50 percent output to allow work on the level control, the spokesman said.

He declined to say how long the repair would take, but said no problems had surfaced late Friday.

On Thursday, the unit was operating at full power after ramping up this week from a refueling outage that began on April 20.

The Ginna station, which entered service in 1970, is located in Ontario in Wayne County, about 20 miles east of Rochester, New York.

One MW powers about 800 homes in New York.

In 2004, the NRC renewed the plant's original 40-year operating license for another 20 years until 2029.

Constellation, of Baltimore, owns and operates more than 8,000 MW of generating capacity, markets energy commodities in North America, and transmits and distributes electricity to 1.2 million customers and natural gas to 640,000 customers in Maryland. (Reporting by Joe Silha and Eileen O'Grady, editing by Jim Marshall)