Completion of the first new reactor at Plant Vogtle may be pushed back into 2017, Southern Co. executives told Georgia regulators Tuesday, although the utility has yet to reach an agreement on the schedule with its contractors.

Speaking before the Georgia Public Service Commission, Southern Nuclear construction support Vice President David McKinney described the current November 2016 and 2017 completion targets as “theoretically achievable,” Georgia Public Broadcasting reported. The Shaw Group and Westinghouse, though, have not committed to that timeline and expect the reactors will be done at least a few months later.

Reasons for the potential delay include worker training, increased project oversight and regulatory requirements, the Atlanta Journal-Constitution reported. Negotiations are ongoing on the estimated completion date, which the contractors put at early- to mid-2017 for unit 3. Unit 4 will come on line a year later. Southern has not yet estimated additional costs associated with a longer timeline.

Significant progress has been made on the reactors' nuclear islands, base mats and modular containment structures. The original completion target for the first unit was pushed back earlier, from April 2016 to November of the same year because of regulatory and other delays.