NEW YORK - Exelon Corp's 867-megawatt Unit 3 at the Dresden nuclear power station in Illinois started to exit an outage and ramped up to 15 percent power by early Wednesday, the U.S. Nuclear Regulatory Commission said in a report.

The unit shut on Oct. 3 when a main steam valve closed.

The main steam valve controls the flow of steam to the plant's turbine generator and is one of several redundant safety systems.

The 1,734 MW Dresden station is located in Morris in Grundy County about 60 miles southeast of Chicago. The plant's two 867 MW Units 2 and 3 entered service in 1970 and 1971.

Unit 2 meanwhile continued to operate at 98 percent of capacity.

Traders noted Unit 2 would likely shut for a month-long refueling and maintenance outage in early November.

Unit 2 last shut for refueling from about Oct. 27-Nov. 20, 2007. It is on a 24-month refueling cycle.

One MW powers about 800 homes in Illinois.

In 2004, the NRC renewed the plant's original 40-year operating licenses for both units for another 20 years until 2029 and 2031.

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