Fission image
Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei.

The fission process produces neutrons and gamma photons and releases a very large amount of energy. This energy can be converted to electricity in nuclear power plants.
At the present time fission is the only nuclear reaction which is successfully used to produce commercial electricity.

More details on fission can be found on the page, Essentials of Nuclear Physics