Nuclear Regulatory Commission Chairman Gregory B. Jaczko prepares to testify on Capitol Hill in Washington on Thursday, Dec. 15, 2011, at a Senate Clean Air and Nuclear Safety subcommittee hearing. (AP Photo/Susan Walsh)

Photo by: Susan Walsh

Nuclear Regulatory Commission Chairman Gregory B. Jaczko prepares to testify on Capitol Hill in Washington on Thursday, Dec. 15, 2011, at a Senate Clean Air and Nuclear Safety subcommittee hearing. (AP Photo/Susan Walsh)