The company operating several nuclear power plants in southern Pennsylvania, including Peach Bottom and Three Mile Island, has fired its security company amid an ongoing probe into guards caught sleeping on duty at Peach Bottom.

Illinois-based Exelon Nuclear terminated its contract Friday with Palm Beach Fla.-based Wackenhut Security. The transition will begin in February at the Three Mile Island power plant and be completed by July, said Craig Nesbit, an Exelon spokesman.