Fissile nuclei are and unstable. They are and decay by alpha decay. However if an extra is incorporated into the nucleus, the nucleus becomes very . It then splits into two or more smaller nuclei, releasing two or more neutrons. The process is called . The neutrons can pass to other nuclei to form a reaction.

The reaction gives off a lot of . If it's uncontrolled, there could be a nuclear explosion. In a , the process is controlled. The reactor acts as a nuclear to turn water into steam to drive a turbine.

Nuclear energy gives off far more heat than the energy in coal.