Source: U.S. Energy Information Administration, based on data from the Form EIA-923, Power Reactor Status Reports.

Note: Nuclear capacity in outage is estimated based on monthly generation data collected by EIA and daily availability data from the Nuclear Regulatory Commission. U.S. Energy Information Administration, based on data from the Form EIA-923, Power Plant Operations Report , and the U.S. Nuclear Regulatory Commission Nuclear capacity in outage is estimated based on monthly generation data collected by EIA and daily availability data from the Nuclear Regulatory Commission.

Outages at U.S. nuclear power plants so far in 2012 are generally higher than in recent years because of extended forced outages at four nuclear power plants. U.S. nuclear reactor operators typically schedule refueling and maintenance outages during the spring and fall to help ensure that reactors are available to meet higher electric demand levels in the summer and winter. The increase in outages at the end of October came as some nuclear power reactors along the East Coast shut down because of safety concerns from Hurricane Sandy.

In 2012, four nuclear power plants had a total of more than four gigawatts of capacity in extended outages:

Southern California Edison's San Onofre Nuclear Generating Station (SONGS) Units 2 and 3 (2,150 MW) near San Diego, California, have both been offline since January 31, 2012, as a precaution after a steam generator tube leak led to the discovery of excessive wear in the plant's new steam generators. The units remain offline while the problems are evaluated and repairs are conducted, which tightened electricity supply for Southern California over the summer. An upcoming Today in Energy article will examine how the local market met demand without these two large units.

Progress Energy Florida's Crystal River Unit 3 (860 MW) has been offline since September 2009 to repair the reactor containment. The plant's future is uncertain at this point, and Progress's handling of the Crystal River repairs became an issue in the company's recent merger with Duke Energy.

Omaha Public Power District's (OPPD) Fort Calhoun reactor (478 MW) has been offline since April 9, 2011, initially due to flooding on the Missouri River. A subsequent inspection by the U.S. Nuclear Regulatory Commission identified additional issues, and OPPD is working through a checklist of repairs and changes to be addressed before restarting the plant. In August, OPPD hired Exelon, a company that operates 17 U.S. nuclear plants, to manage day-to-day operations at Fort Calhoun.

At the Turkey Point plant outside Miami, Florida, Unit 3 (693 MW) went offline in late February 2012 for refueling, then underwent additional repairs through the summer and early fall, and only returned to service in late October.

Because of the low operational cost of producing power at nuclear facilities, these generators are nearly always dispatched whenever they are available. Outages thus have a direct and significant impact on nuclear power generation as well as the mix of total generation in an electric system.