Georgia Power announced this week that Unit 4 at the Vogtle nuclear expansion project near Waynesboro, Georgia, has safely reached initial criticality. Initial criticality is a key step during the startup testing sequence and demonstrates that — for the first time — operators have safely started the nuclear reaction inside the second reactor. This means atoms are being split and nuclear heat is being made, which will be used to produce steam. A reactor achieves criticality when the nuclear fission reaction becomes self-sustaining. Achieving initial criticality is necessary to continue the startup of the unit in order to generate sufficient heat for…