The chief contractor at a failed multibillion-dollar project to build two nuclear reactors in South Carolina has agreed to pay more than $20 million as part of a cooperation agreement with federal authorities probing the fiasco. Acting U.S. Attorney Rhett DeHart said Monday that Westinghouse Electric Co. will contribute $21.25 million to a program intended to assist low-income ratepayers affected by the project's failure. The company will also be required to cooperate with federal investigators still probing the company's role in the 2017 debacle at the V.C. Summer plant, which cost ratepayers and investors billions and left nearly 6,000 people jobless. Three top-level executives have pleaded guilty as part of a multi-year federal fraud investigation.