Unstable isotopes of uranium are used as fuel for nuclear reactors and as payload for nuclear weapons. Preparing uranium for use as a nuclear weapon requires that it be highly "enriched" by separating the unstable atoms from the more stable U-238 atoms using specialized centrifuges. Uranium can also be enriched (to a lesser degree) for use in nuclear reactors, although not all reactor designs require enriched fuel.
Depleted Uranium is elemental Uranium-238 that is left over after all of the fissile isotopes have been removed from the material. Depleted uranium is used in some types of modern armor-piercing ammunition. It has several properties that make it ideal for penetrating armor:
- High density, giving it greater momentum
- Self-sharpening, maintaining a penetrating point when it fractures
- Pyrophoric, burning at high temperatures when it breaks or deforms