ATLANTA (AP) — Southern Co. said Thursday it will exceed its original budget to build a first-of-its-kind nuclear plant, a troubling development for an industry long plagued by cost overruns.

The Atlanta-based utility formally asked regulators to raise its budget to build two more nuclear reactors at Plant Vogtle (VOH’-gohl) by about $737 million to roughly $6.85 billion. Additional costs are possible. Companies designing and building the plant have sued the utility seeking $425 million for unexpected project costs, though the utility has filed its own suit and denies responsibility for those expenses.