Nuclear reactor

Nuclear reactor, device containing sufficient fissionable material to produce a controlled chain reaction of neutrons able to split other nuclei. Many types of reactors exist; all produce neutrons, gamma rays, radioactive fission products, and heat. A fission reactor consists of a fuel, a moderator, and a cooling system. The fragments produced by fission of a heavy nucleus have a large amount of energy, and the heat they produce may be used for carrying out a variety of high-temperature processes or for heating a working fluid (such as steam) to operate a turbine and produce electricity. Nuclear reactors are also used to power ships and submarines. The 1979 accident at Pennsylvania's Three Mile Island reactor—involving a partial fuelcore meltdown and the release of radioactive gases into the atmosphere—brought the issue of nuclear safety to the public. Concern for safety increased with the 1986 explosion and fire at a nuclear power plant at Chernobyl in the former USSR.