Nuclear fuel is a material that can be consumed in a nuclear reactor to produce energy, sustain a nuclear chain reaction, and/or achieve a desired energy output. Nuclear fuel generally consists of two parts - a fissile material, capable of sustaining a controlled chain reaction, and a fission product, which is a material that absorbs radiation. In the most common reactor designs, the fuel is enriched uranium or plutonium, with an array of the fission product, usually boron or cadmium. When the fuel becomes contaminated with fission products it must be replaced, as it loses its ability to sustain a reaction.

See also: nuclear power, nuclear weapon, fossil energy, nuclear exchange, fossil carbon