The energy liberated by (1) the splitting or fission of an atomic nucleus, (2) the union or fusion of two atomic nuclei, and (3) the radioactive decay of a nucleus (transmutation). For details refer to the following entries; nuclear reaction, fission, fusion, tokamak, radioactivity, ionizing radiation, nuclear chemistry, transmutation, breeder, uranium-235, plutonium, nuclear reactor.See Acceptable Risk.