Nuclear power provides clean electricity at a very low cost, and it does not produce greenhouse gases. However, the reaction at the heart of nuclear power produces radioactive wastes. The potential danger from escaped radiation from an accident has given nuclear power a fearsome reputation. Since the near-disaster in 1979 at Three Mile Island, in the United States, and the terrible accident in 1986 at Chernobyl, Ukraine, nuclear-energy producers have taken great strides to make their plants safer. In a world where polluting emissions have become a bigger and bigger concern, nuclear power will be a significant piece of the energy-production puzzle.