The Energy Department said Tuesday that scientists at a federal research facility had achieved a breakthrough in research on nuclear fusion, long seen as a potential source of clean, virtually limitless energy and a key tool in efforts to curb climate change.A controlled fusion reaction at Lawrence Livermore National Laboratory in Livermore, Calif., produced more energy than it consumed, Energy Secretary Jennifer Granholm said during a press conference from DOE headquarters in Washington, D.C.Continue reading your article witha WSJ membershipa WSJ membershipAlready a member?Sign In"