Long-anticipated legislation to pump hundreds of millions of ratepayer dollars into Pennsylvania’s five nuclear power plants is being introduced. Monday’s bill unveiling could usher in heated debate over whether the plants deserve what critics call a bailout. The debate will run up against a June 1 deadline. That’s when Three Mile Island’s owner, Chicago-based Exelon, says it’ll start shutting down the financially struggling plant that was the site of a partial meltdown in 1979.