Georgia Power said Tuesday it has ordered the first nuclear fuel load for its Plant Vogtle unit 3 reactor under construction south of Augusta.

The order is the first for a new U.S. reactor "in more than 30 years," the company said in a statement.

The 157 uranium fuel assemblies will be loaded into the unit 3 reactor vessel once it begins operating in late 2021. The 14-foot tall assemblies also will eventually be ordered for unit 4, which is expected to come online in 2022.

However, the Georgia Public Service Commission said in its April review of the project, released Tuesday, that those dates "will be a challenge to achieve." It also said in the review the $17.1 billion project cost could rise if the completion date is not met.

Total employment at the units 3 and 4 construction site have reached 8,000 workers, making it the largest construction project in the state, the company said. When complete, the new reactors will create 800 permanent jobs.

The unit 3 containment vessel top was placed earlier this year during a visit from U.S. Energy Secretary Rick Perry, Gov. Brian Kemp, U.S. Agriculture Secretary Sonny Perdue and all five members of the Georgia PSC.

Roughly one-third of the reactor fuel in units 3 and 4 will be replaced every 18 months during scheduled refueling and maintenance periods, similar to units 1 and 2.

Georgia Power said Tuesday it also has completed placing three low-pressure turbine rotors and the generator rotor inside the unit 3 turbine building. The 200-ton turbine rotors allow steam to spin the generator at 1,800 revolutions per minute to supply electricity to the power grid. The high-pressure turbine rotor will be installed in the coming weeks, the company said.

Georgia Power is the lead owner of the project, which is co-owned by Oglethorpe Power, a supplier of power to electric membership cooperatives; MEAG Power, an electric supplier for city-owned utility companies; and Dalton Utilities, the electric utility for the city of Dalton, Ga.