Uranium is enriched through a physical process that increases the proportion of the uranium-235 (U-235) isotope relative to uranium-238 (U-238), as U-235 is the isotope that is useful for nuclear fission. Here is how uranium is typically enriched:
- Conversion to Gas: Natural uranium is first converted into uranium hexafluoride (UF6), a gaseous form suitable for processing.
- Gas Centrifuge Method: The UF6 gas is fed into centrifuges that spin at very high speeds. The centrifugal force separates the isotopes because U-235 is slightly lighter than U-238. The heavier U-238 moves toward the outside of the centrifuge, while the lighter U-235 concentrates closer to the center. This process results in slightly enriched UF6 gas near the center and depleted UF6 near the periphery.
- Cascading Centrifuges: This separation is repeated many times in a series of gas centrifuges arranged in cascades, progressively increasing the concentration of U-235 until the desired enrichment level (usually between 3% and 5% for nuclear fuel) is reached.
- Cooling and Compressing: The enriched uranium gas is then compressed and cooled, turning back into a solid or liquid form for further processing into nuclear fuel.
Older methods such as gaseous diffusion, which uses porous membranes to separate isotopes based on molecular weight, have largely been replaced by centrifuge technology due to the latter's greater efficiency. There are also laser-based enrichment methods under development, where isotopes are separated using laser excitation, but these are not yet widely used. In summary, uranium enrichment mainly involves converting uranium into a gas and spinning it at high speeds in centrifuges, which separate the isotopes by mass difference to increase the U-235 content for use in reactors or weapons.
