The Energy Information Administration (EIA) reported summer capacity factors for the nation’s fleet of nuclear power plants. No fewer than 21 nuclear units had capacity factors that exceeded 100%.

And Nine Mile Point Nuclear Station unit 2 in New York topped the list in 2021, with a 111.4% summer capacity utilization factor. Altogether, 93 reactors were in operation at the time.

According to EIA data, 21 reactors achieved a capacity factor above 100% last year:

U.S. reactors have supplied around 20% of the nation’s power since the 1990s and are the largest producer of nuclear energy in world.

According to the U.S. Department of Energy (DOE), nuclear energy provided half of America’s carbon-free electricity in 2021, making it the largest domestic source of clean energy.    

Nine Mile Point’s two reactor units have generation capacity of more than 2 GW. Unit 1 was commissioned in 1969 and is the nation’s oldest commercial power reactor. The plant is operated by Constellation Energy.

Capacity factors measure how intensively a generating unit runs. EIA said it calculates capacity factors by dividing the actual electrical energy produced by a generating unit by the maximum possible electrical energy that could have been produced if the generator operated at continuous full power.

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