UPDATE 1-Gas explosion at Exelon Ill. nuke plant outbuilding

(Updates with company report to NRC)

NEW YORK, Oct 27 (Reuters) - A gas explosion rocked an outbuilding near Exelon Corp's EXC.N 1,734-megawatt Quad Cities nuclear power plant in Illinois early Monday, the company said in a release.

There were no injuries to plant personnel, no damage to equipment and at no time was there any concern for the health and safety of the public, the company said, adding there was no radiological release.

In an event report to the U.S. Nuclear Regulatory Commission, the company said the cause of the explosion appeared to be related to a buildup of some kind of hydrocarbon gas.

Both Quad Cities reactors continued to operate at full power. The outbuilding, about 100 yards from the power generating portion of the plant, houses a rarely used tank and pump for storing floor drainage from the plant.

Plant operators were investigating the cause of the blast.

The explosion prompted the company to declare an “unusual event,” which is the lowest of the NRC’s emergency classifications.

The 1,734 MW Quad Cities station, which entered service in 1972, is located in Cordova in Rock Island County, about 155 miles west of Chicago. There are two 867 MW Units at the station.

Unit 1 continued to operate at 98 percent power.

One MW powers about 800 homes in Illinois.

In 2004, the NRC renewed the plant’s original 40-year operating licenses for another 20 years until 2032.

Exelon's Exelon Generation Co LLC subsidiary operates the station for its owners, Exelon (75 percent) and Berkshire Hathaway Inc's BRKa.N MidAmerican Energy Co subsidiary (25 percent).

Exelon, of Chicago, owns and operates more than 38,000 MW of generating capacity, markets energy commodities, and transmits and distributes electricity to about 5.4 million customers in northern Illinois and southeast Pennsylvania and natural gas to about 480,000 the Philadelphia area. (Reporting by Scott DiSavino; Editing by John Picinich)