EIA data show that U.S. nuclear power plants generated 778 million megawatthours of electricity in 2021, which was 1.5% less than the previous year. It was the second consecutive annual decline. Nuclear supplied 19% of U.S. electricity generation across all sectors in 2021, similar to its average share over the previous decade.

Six nuclear generating units with a total capacity of 4,736 MW had retired since the end of 2017 at the time of the analysis. EIA listed three more reactors with a combined 3,009 MW of capacity as scheduled to retire in the coming years. They were Michigan's Palisades, plus one unit each at California's Diablo Canyon in 2024 and 2025.

The retirement of Indian Point Unit 3 in 2021 reduced output, and a higher capacity factor at the remaining fleet offset part of the loss. Capacity factor measures how much of the time a unit operates. The U.S. nuclear fleet has averaged an annual capacity factor of at least 90% in every year since 2012, and the 2021 average was 93%. Nuclear units run more of the time than almost all other electricity-generating technologies.

EIA attributed retirements mainly to financial pressure in competitive wholesale power markets. Four units at two sites in Illinois reversed plans to retire after state incentives supported their continued operation.

The agency's chart pairs nuclear capacity additions and retirements. Vogtle Units 3 and 4 in Georgia, each rated at 1,114 MW, were then under construction and planned to come online by the end of 2023. They would be the first new units since Watts Bar Unit 2 in Tennessee in 2016.

Source: U.S. Energy Information Administration - https://www.eia.gov/todayinenergy/detail.php?id=55027