Sign up for daily news updates from CleanTechnica on email. Or follow us on Google News!. According to the New York Times, Constellation Energy plans to reopen the shuttered Three Mile Island nuclear plant in Pennsylvania, the site of the worst reactor accident in United States history. Three Mile Island became infamous when one of its two reactors partly melted down in 1979. The other reactor kept operating safely for decades until finally closing, for economic reasons, five years ago.