An inexhaustible supply of energy.
Nuclear energy is a form of energy derived from the radioactive decay of uranium.
Like almost all forms of energy, what the radiation does is to generate heat. The amount of energy available from uranium is many orders of magnitude more that what is available from the equivalent amount of coal. Each is radioactive, but only the 235 U is fissionable in a nuclear reactor. A fast moving neutron bombards the nucleus of a 235 U atom. These neutrons can then bombard other 235 U atoms.