COLUMBIA, S.C.  — The owners of two nuclear reactors under construction in South Carolina decided Monday to cease operations at the project, which has been beset by delays and cost overruns.

While the decision will save customers billions in additional costs, the two utilities may get little to nothing refunded of the billions they’ve already paid for the now-abandoned project.

The reactors were set to be among the first built in the U.S. in decades.

Santee Cooper’s board said the decision to end construction will save customers an estimated $7 billion. The utility had already spent about $5 billion for its 45 percent share of the project, and completing it would have cost an additional $8 billion, plus $3.4 billion in interest. It also likely wouldn’t have been finished until 2024. The first reactor initially was supposed to be online earlier this year.

South Carolina Electric & Gas, which owns 55 percent, announced its plans shortly after Santee Cooper’s unanimous vote. That utility’s executives will brief state regulators Tuesday.

“It became obvious to us” to end construction, said Santee Cooper CEO Lonnie Carter.

Under the approved Santee Cooper resolution, all work will end within six months. How quickly within that timeframe workers at the site will lose their jobs is uncertain.

The project has been shrouded in doubt since earlier this year, when primary contractor Westinghouse filed for bankruptcy protection.

The utilities announced last week that Westinghouse’s parent company, Toshiba Corp., agreed to jointly pay them $2.2 billion regardless of whether the reactors are ever completed.