To make a nuclear fuel, you prepare a cocktail of uranium in a very precise blend. You need a large quantity of uranium 238 and between 3 and 5% of uranium 235. Without this careful dosing of the two, no chain reaction… Zero energy produced.
Because nature does things well, the uranium extracted already contains both isotopes. But not in the right proportions: 99.3% of U238 for just 0.7% of U235. So you have to increase the amount of U235, i.e. enrich it. The uranium must first be converted from its solid form into its gaseous form by heating it at a relatively low temperature.
Then you separate the two isotopes.
By turning the gas in a centrifuge, the heavier U238 migrates to the outside, leaving the U235 in the center. You then simply recover the U235 and add it to the uranium 238. Once you have the ideal proportion, you can make great nuclear fuels.
This process of centrifugation, which is very water and energy efficient, is used by AREVA at its George Besse II enrichment plant. For one ton of uranium processed, you obtain 120 kilograms of enriched uranium – used to fabricate conventional nuclear fuels – and 880 kilograms of depleted uranium which feeds into the production of recycled fuel known as MOX.