Wall Street Journal: As Congress debates whether to limit carbon-dioxide emissions, one of the most vocal supporters of such legislation — the nuclear-power industry — is poised to reap a multibillion-dollar windfall if restrictions take effect. Some nuclear operators are already forecasting how much their profits could increase under various versions of greenhouse-gas legislation that are under consideration. Among the nuclear operators that stand to profit most are Exelon Corp., FPL Group Inc., …