Two reactors under construction at South Carolina's V.C. Summer nuclear plant will come online later than expected, Scana executives said last week.

The completion date of unit 2 was pushed back from March of 2017 to the end of that year or into the first quarter of 2018, Scana Senior Vice President Stephen Byrne said in a call with analysts. Work on unit 3 is six months to a year behind unit 2.

Summer nuclear plant unit 2 containment vessel bowl. Source: ScanaBoth units are Westinghouse AP1000 reactors originally under construction by Westinghouse and the Shaw Group, before the latter company was purchased by Chicago Bridge & Iron. Executives blamed the delay on a former Shaw submodule manufacturing plant in Lake Charles, La., noting that the facility has had some "startup issues," as well as documentation and quality issues that have drawn scrutiny from the Nuclear Regulatory Commission.

Through its South Carolina Electric and Gas subsidiary, Scana owns 55 percent of the project, previously estimated to cost $9.8 billion. Byrne said the delays would cause Scana's portion of that cost to increase by as much as $200 million.

Substantial progress has been made at the site, which recently saw completion of the unit 2 basemat and the placement of the lower containment vessel bottom head (shown at left.) The project remains within a broader time frame approved earlier by state regulators.