Fission and Fusion

Nuclear Fission

If the nucleus of a heavy atom–such as uranium–absorbs a neutron, the nucleus can become unstable and split. This is called nuclear fission. Fission releases energy in the form of heat. Although fission can occur naturally, fission as encountered in the modern world is usually a deliberate man-made nuclear reaction.

Typical fission events release about two hundred million eV (200 MeV) of energy. In contrast, most chemical oxidation reactions (such as burning coal) release at most a few eV per event. So, nuclear fuel contains at least ten million times more usable energy per unit mass than does chemical fuel.

Nuclear Fusion

Fusion is the opposite reaction of fission. In fusion, atoms are fused together.
For a fusion reaction to occur, it is necessary to bring two nuclei so close that nuclear forces become active and glue the nuclei together. Deuterium and Tritium, isotopes of hydrogen, are used in fusion reactors. Nuclear forces are small-distance forces and have to act against the electrostatic forces where positively charged nuclei repel each other. This is the reason nuclear fusion reactions occur mostly in high density, high temperature environment.

Recreating that environment is the greatest challenge to producing commercial scale fusion energy, but it’s a challenge well worth pursuing. Nuclear fusion can produce four times the amount of energy as nuclear fission.