But in written testimony filed with the Georgia Public Service Commission, Southern Company officials also said a schedule lapse in recent months has been corrected, and that they remain optimistic that a federal combined operating license will be issued for the $14.8 billion project without long delays.
The testimony from Jeffrey Burleson, Southern Company's vice president of system planning and Pete Ivey, Southern Nuclear's vice president of nuclear development, was filed in response to assertions made June 10 by nuclear engineer William Jacobs, appointed by the commission to monitor the project.
Jacobs warned that unresolved design certification issues with the AP1000 reactors that will be used at the site are among several factors that could inflate costs and create construction delays.
He also cautioned that Southern Nuclear's plan to bring the new units online in 2016 and 2017 are based on the assumption the U.S. Nuclear Regulatory Commission will license the project this year.
Burleson and Ivey said officials expect the NRC to act on the license request this year, but also acknowledged the possibility of delays and higher costs.
"Due to the nature and complexities of this large project, including the fact that it is being licensed and constructed under the Nuclear Regulatory Commission Part 52 licensing process that has never been vetted before, it is possible that Dr. Jacobs' observation - which is that the project may exceed its current schedule and budget - also reflects a possible outcome," they said.
At the time of Jacobs' testimony in June, they added, the schedule for Unit 3 was tracking a few months behind. Since then, those delays have been corrected and the project is now on schedule again.
They also agreed with Jacobs' testimony about the potential of licensing delays that could affect project schedules.
"Despite Congressional and NRC efforts to improve the licensing process, we cannot disagree with Dr. Jacobs that there are challenging uncertainties," they said.
The company has projected commercial operation dates of April 1, 2016, and April 1, 2017, for Unit 3 and Unit 4, respectively.