Courtesy Georgia Power

Unite 4 concrete mat will serve as the foundation for all of the nuclear island structures, including the containment vessel and the shield building.

Workers at the Plant Vogtle nuclear expansion project on Nov. 21 completed placement of basemat structural concrete for the nuclear island at Unit 4, according to plant owner/operator Georgia Power. The utility called the placement "a significant accomplishment in the construction of the project."

Georgia Power, which owns 45.7% of the two planned 1,117-MW units, said the placement of about 7,000 cubic yards of concrete was finished in only 41 hours, which it said "matches the best time achieved worldwide" for similar work on other Westinghouse AP1000 units. Workers placed the basemat concrete for Unit 3 in March.

The basemats will serve as the foundation for the nuclear island structures in both units, including the containment vessel and the shield building.

"The containment vessel bottom head and supporting CR10 cradle are completed and will be placed on the Unit 4 nuclear island following concrete curing," Georgia Power said in a statement. "In parallel, the Unit 4 turbine building foundation has been completed and wall sections are currently being placed that also will take the turbine building to grade elevation."

The Plant Vogtle expansion project is being built by Westinghouse and Chicago Bridge & Iron. In addition to Georgia Power, owners of the project include Oglethorpe Power, with 30%; Municipal Electric Authority of Georgia, with 22.7%, and the municipal utility in Dalton, Ga., with 1.6%. Unit 3 is scheduled to begin commercial operation in the fourth quarter of 2017, with Unit 4 to follow about a year later.