* Autumn 2012 outages seen at 18,200 MW
* Outages reached 19,900 MW in autumn of 2011
* Five-year autumn outage average 20,400 MW (Adds background, details)
July 25 (Reuters) - About 18,200 megawatts (MW) of nuclear power capacity is expected to be out of service in the United States in the upcoming autumn refueling season, according to Reuters data.
That is roughly 9 percent, or 1,700 MW, below the 19,900 MW of nuclear capacity that was shut last year during mid-October, the height of the autumn refueling season, the data showed.
The data assumes units currently on extended outages -- like the San Onofre reactors in California -- will still be shut in mid-October.
Southern California Edison, the unit of California power company Edison International that operates San Onofre, has not given a return date and so it is still possible though unlikely the reactors could return before the autumn refueling season.
Nuclear outages over the past five years have averaged about 20,400 MW in autumn (2007-2011) and 23,000 MW in spring (2008-2012). See
Since 1999, autumn outages peaked near 27,200 MW in 2009 and bottomed at about 12,300 MW in 2004. Spring outages have peaked at 32,800 MW in 2011 and bottomed at 16,100 MW in 2004.
The 104 U.S. nuclear power reactors are capable of generating almost 101,200 MW of electricity, enough to power about 80 million homes.
Nuclear reactors operate around the clock as baseload facilities, providing some of the lowest-cost power.
Natural gas traders follow the nuclear outages closely because plants burning gas usually make up much of the missing nuclear generation, especially during periods of high demand.
It takes about 200 million cubic feet of natural gas per day to generate about 1,000 MW of electricity. One billion cubic feet of gas could generate about 5,000 MW of electricity. (Reporting by Naveen Arul and NR Sethuraman in Bangalore and Scott DiSavino in New York; editing by John Wallace and David Gregorio)