More than one-third of the United States’ nuclear power fleet — 21 of 60 facilities that provide low-carbon electricity — will be or could be shuttered in the next decade before their operating licenses expire and replaced primarily by natural gas and coal, according to an analysis released today by the Union of Concerned Scientists (UCS) that assessed the economic viability of the U.S. nuclear power industry. The plants, which are mostly smaller, single reactor plants, provide more than one-fifth of the country’s nuclear power.

According to the report, early nuclear retirements pose no threat to the nation’s electricity reliability and resilience. The threat is the potential replacement of their low-carbon electricity with fossil fuels.

“The United States is facing a dilemma,” said Steve Clemmer, co-author and director of energy research and analysis at UCS. “Nuclear power plants are being squeezed economically at a time when we need every source of low-carbon power we can get to replace retiring coal plants and prevent an overreliance on natural gas. Strong policies can prevent the abrupt closure of nuclear plants that meet stringent safety standards, while we continue to ramp-up investments in renewables, efficiency and other low carbon technologies to drive down emissions.”