MINNEAPOLIS — A contractor is suing Xcel Energy Inc. alleging $45 million in unpaid cost overruns during an 18-month overhaul of the Prairie Island nuclear power plant near Red Wing.

Charlotte, N.C.-based contractor Babcock & Wilcox Nuclear Energy contends Xcel Energy has refused to pay the full cost for replacing a pair of massive steam generators at the plant’s Unit 2. The project was completed last December.

Xcel Energy told Minnesota regulators the project cost $285 million. If the $45 million in disputed charges are added to that, it represents a 16 percent cost overrun.

An Xcel Energy spokeswoman said the lawsuit is solely about claims for additional payment that the company considers without merit. She said Xcel Energy will file a response within 20 days.