JACKSON (AP) — After a March 9 tubing leak, Mississippi Power Co. said Thursday that it’s unsure when its $7.1 billion Kemper County power plant will be finished.

With the plant three years behind schedule, Atlanta-based Southern Co. said in a stock filing that it won’t meet the latest deadline of mid-March.

Kemper is designed to capture 65 percent of the carbon dioxide from the burning coal, releasing only as much of the climate-warming gas as a typical natural gas plant does.

Kemper’s two gasifiers convert soft lignite coal mined at the site into a synthetic gas using high pressure and heat. The tubes broke in a cooling unit that reduces the heat of the gas that comes out of the gasifier before piping it into a chemical plant that removes carbon dioxide and other chemicals. The gas is then burned in turbines to generate electricity

Spokesman Jeff Shepard said the company has started repair work and doesn’t have to repair the other gasifier.

“It’s not a design problem,” he said. “It’s repairing some leaks.”

Shepard said Mississippi Power is still evaluating how much longer the delay will set back the plant. Time is money at Kemper: The utility says a month’s delay would force the company to absorb another $25 million to $35 million in losses. Customers, meanwhile, could be asked to pay another $20 million in interest and legal costs.

Southern shareholders have already absorbed $2.8 billion in losses from the plant, while Mississippi Power’s 186,000 customers could ultimately be asked to pay $4.2 billion.

Mississippi Power must submit a rate plan to the state Public Service Commission by June 3. That elected three-member regulatory body will ultimately decide how much the company can recover. The PSC granted Mississippi Power a rate increase in 2015 covering $840 million worth of assets that began generating electricity burning conventional natural gas.