Australian Safeguards and Non-Proliferation Office

Definitions

Natural uranium
- uranium as it occurs in nature, having an atomic weight of approximately 238 and containing minute quantities of 234U, about 0.7%, 235U and 99.3% 238U.  Natural uranium is usually supplied in raw form by uranium mines and concentration (ore processing) plants as uranium ore concentrate, most commonly the concentrated crude oxide U3O8, often called yellow cake.
Depleted uranium
- uranium in which the abundance of the isotope 235U is less than that occurring in natural uranium. E.g. uranium in spent fuel from natural uranium fuelled reactors and tails from uranium enrichment processes.
Enriched uranium
- uranium having a higher abundance of fissile isotopes than natural uranium.  Enriched uranium is considered a special fissionable material.
Low enriched uranium (LEU)
- enriched uranium containing less than 20% of the isotope 235U.  LEU is considered a special fissional material and an indirect use material.
High enriched uranium (HEU)
- uranium containing 20% or more of the isotope 235U.  HEU is considered a special fissionable material and a direct use material.
Uranium 233
- an isotope of uranium which is produced by transmutation of 232Th through irradiating thorium fuel in a reactor.  Uranium-233 is considered a special fissionable material and a direct use material.
Plutonium
- a radioactive element which occurs only in trace amounts in nature, with atomic number 94 and symbol Pu.A produced by irradiating uranium fuels, plutonium contains varying percentages of the isotopes 238, 239, 240, 241 and 242.  Plutonium containing any 239Pu is considered a special fissionable material and, except for plutonium containing 80% or more of 238Pu, a direct use material.
Thorium
- a radioactive element with atomic number 90 and symbol Th.  Naturally occurring thorium consists only of the fertile isotope 232Th, which through transmutation becomes the fissionable 233U.