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A reactor operator works in the control room at the Exelon Corp. Three Mile Island nuclear power plant in Middletown, Pennsylvania, U.S., on Wednesday, April 11, 2018. On Sept. 30, Exelon Corp. plans to take Three Mile Island offline because it is no longer profitable. Across the U.S., Nuclear plants are having trouble staying competitive in an era of cheap natural gas, a product of the shale boom. Photographer: Michelle Gustafson/Bloomberg via Getty Images

A reactor operator works in the control room at the Exelon Corp. Three Mile Island nuclear power plant in Middletown, Pennsylvania, U.S., on Wednesday, April 11, 2018. On Sept. 30, Exelon Corp. plans to take Three Mile Island offline because it is no longer profitable. Across the U.S., Nuclear plants are having trouble staying competitive in an era of cheap natural gas, a product of the shale boom. Photographer: Michelle Gustafson/Bloomberg via Getty Images