Exelon Generation, operator of the largest nuclear reactor fleet in the United States, intends to downsize that fleet next year by retiring its Byron and Dresden plants. In an announcement released early this morning, Exelon said that the two-unit Byron, located near Byron, Ill., would be permanently closed in September 2021, followed in November by the two-unit Dresden, located in Morris, Ill.

Byron is licensed to operate for another 20 years; Dresden, a much older facility, is licensed for another decade.