Fission processes take nuclei (for example, Uranium) and split them. In the process of splitting the atom, a huge amount of energy is released. However, the downside is that the smaller atoms that are formed by the process are typically radioactive. Nuclear reactors can utilize the fission process to generate electricity, and nuclear bombs are simply an uncontrolled fission process driven by a chain reaction.

Fusion processes, on the other hand, take smaller nuclei and combine them together to make a larger nucleus. The fusion process also releases a lot of energy. However, the difficulty with this process is getting two nuclei (both positively charged) to collide and combine. Controlling the fusion process to generate electricity has not yet been demonstrated, although an uncontrolled process can be used in weapons. Also, the appropriate conditions for fusion also exist in extreme conditions such as in stars. For example, the sun's nuclear process is a fusion process.