#GS-03 Science and Technology
- Enriched uranium is a type of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation.
- Naturally occurring uranium is composed of three major isotopes: uranium-238, uranium-235, and uranium-234.
- When uranium is mined, it consists of approximately 99.3% uranium-238 (U238), 0.7% uranium-235 (U235), and < 0.01% uranium-234 (U234).
- The commercial process employed for this enrichment involves gaseous uranium in centrifuges.
- Most reactors are light water reactors and require uranium to be enriched from 0.7% to 3-5% U-235 in their fuel.
- Uranium-235 and U-238 are chemically identical, but differ in their physical properties, notably their mass.
- The nucleus of the U-235 atom contains 92 protons and 143 neutrons, giving an atomic mass of 235 units.
- The U-238 nucleus also has 92 protons but has 146 neutrons – three more than U-235 – and therefore has a mass of 238 units.
- The 1.27% difference in mass between U-235 and U-238 allows the isotopes to be separated and makes it possible to increase or “enrich” the percentage of U-235.
- All present and historic enrichment processes, directly or indirectly, make use of this small mass difference.
- Enrichment processes require uranium to be in a gaseous form at relatively low temperature.
- Hence uranium oxide from the mine is converted to uranium hexafluoride (UF6) in a preliminary process, at a separate conversion plant.
- The two primary hazards at enrichment facilities include chemical hazards that could be created from a UF6 release and criticality hazards associated with enriched uranium.
There are several enrichment processes utilized worldwide. They are:
- Gaseous Diffusion
- Gas Centrifuge
- Laser Separation