Capacity outages at U.S. nuclear power plants averaged 3.1 gigawatts this summer

Daily capacity outages at U.S nuclear power plants averaged 3.1 gigawatts (GW) during the summer of 2021 (June 1 through August 31), 22% less than the 4.0 GW average in summer 2020. Nuclear capacity outages were lowest in August, when they averaged 1.7 GW for the month.

U.S. nuclear outages are usually at their lowest during summer and winter because electricity demand is high during these seasons and plant operators try to ensure plants are available to meet the increased electricity demand associated with air conditioning and electric heating.

Planned nuclear outages are usually scheduled to coincide with a plant’s refueling cycle. U.S. nuclear power plants typically refuel every 18 to 24 months, mostly in fall and spring when electricity demand is lower. During a refueling outage, plants typically optimize downtime by scheduling facility upgrades, repairs, and other maintenance work while the nuclear reactor is offline.

So far in 2021, the average refueling outage lasted 32 days. Over the last few decades, the average duration of a refueling outage for a nuclear power plant in the United States has decreased—the average duration in 2021 was 27% shorter than the 44-day average in 2000.

Unplanned, or forced, nuclear generation outages can result from equipment failure, operational error, environmental conditions, or external circumstances such as severe weather. So far in 2021, 34 unplanned nuclear outages have occurred, 14 of which occurred over the summer. The mid-June 2021 summer outage peak is partly attributable to unplanned outages at Wolf Creek Generating Station in Kansas, Comanche Peak in Texas, and Edwin I Hatch in Georgia.

Early retirements are also classified as unplanned outages in the data. Early retirements affected the amount of available summer nuclear capacity in 2021. The Indian Point Energy Center in New York retired its last operating reactor (Unit 3) at the end of April 2021, earlier than originally planned, removing 1.0 GW of nuclear generating capacity from the grid.

Our Status of Nuclear Outages page, which is based on data collected by the U.S. Nuclear Regulatory Commission and EIA’s surveys of the electric power sector, provides daily operation information on each commercial U.S. nuclear power reactor.

Principal contributors: Elesia Fasching, Slade Johnson