Georgia Power has begun the process of loading fuel into the Vogtle plant’s Unit 4 reactor, the company announced yesterday, marking another pivotal milestone toward commercial operation of the second of the facility’s two new units.

The Nuclear Regulatory Commission has authorized Southern Nuclear Operating Company to begin loading fuel into Unit 4 at the Vogtle nuclear expansion site near Waynesboro, Ga., making the unit the second reactor to reach this milestone in the agency’s combined license process—a little less than one year after Vogtle-3. (Prior to 1989, reactors were licensed under a two-step process, requiring both a construction permit and an operating license.)

Georgia Power announced this morning that fuel loading at Vogtle-3 has commenced, marking an important milestone on what has proved to be a long and bumpy road to startup and commercial operation of the first new nuclear power reactors to be built in the United States in more than three decades. (Major work on the Vogtle-3 and -4 project began in 2012, with a price tag of $14 billion and scheduled unit start dates of 2016 and 2017. The project’s total cost is now expected to exceed $30 billion.)