For the first time in almost seven years, a new nuclear reactor has started up in the United States. On Monday, March 6, 2023, Georgia Power announced that the Vogtle nuclear reactor Unit 3 has started a nuclear reaction inside the reactor. Technically, this is called “initial criticality.” It’s when the nuclear fission process starts splitting atoms and generating heat. Vogtle’s Unit 3 reactor will be fully in service in May or June 2023. The last time a nuclear reactor reached the same milestone was almost seven years ago in May 2016 when the Tennessee Valley Authority started splitting atoms at the Watts Bar Unit 2 reactor in Tennessee.