South Carolina Electric & Gas Company has annouced that the concrete basemat for unit 3 of the VC Summer AP1000 nuclear power plant was completed on 4 November.

The milestone comes just seven months after first concrete for VC Summer 2, and brings the number of reactors under construction in the United States to five.

The 6-foot thick concrete basemat provides a foundation for the containment and auxiliary buildings that are within the nuclear island. Around 7000 cubic yards of concrete was needed for the concrete pour, which covered an area of 32,000 square feet.

Nearly 500 people worked for 43 hours and 25 minutes over the weekend of the 2-3 November, continuously pouring the concrete, according to Jeff Benjamin, nuclear power plants senior vice president at Westinghouse Electric Company. Westinghouse and its consortium partner Chicago Bridge & Iron Company (formerly Shaw Group) were awarded an engineering and procurement contract for the two units in 2008.

"Thanks to the lessons we learned from the Unit 2 concrete pour and also from our other construction projects, we were able to complete this milestone safely and even more efficiently," Benjamin said. The concrete pour for VC Summer 2, completed on 11 March 2013 took a total of 51.5 hours.

Benjamin also said that there has been "significant progress" on Summer 2.

"Some of the progress includes the placement of the containment vessel bottom head and placement of the reactor vessel support module, as well as concrete placement that will enable further progress on the nuclear island," Benjamin said.

One of the cooling towers is almost complete, and work continues on major modules, the containment vessel and auxiliary building.

SCE&G and Santee Cooper are planning two 1117 MW Westinghouse AP1000 reactors at the existing VC Summer site in South Carolina. Summer 2 is currently scheduled to be complete in "late 2017 or early 2018," according to SCE&G. It will be followed by Summer 3.

Once the units begin operation SCE&G anticipates its generation mix will be about 30% nuclear, 30% natural gas, and 30% scrubbed coal, with the balance in hydro, solar and biomass.

Photo: Concrete pour for Summer 2 in March 2013. Summer 3 basemate was completed on 4 November (Source: SCANA)