Discovered two hundred years ago, uranium is one of the most widely distributed elements on earth. Much like lead, and more so than tin or silver. Uranium is a radioactive element present everywhere in the natural environment: one cubic metre of earth in an ordinary vegetable garden contains around 40 grams of uranium.
Uranium ore is extracted from sites where it is present in high concentrations. The ore is crushed in order to separate the uranium from it. It is then concentrated in multiple stages: purification, precipitation, washing, filtering, etc. The result is a 'yellow cake', which is about 75% uranium. In the yellow cake, only uranium 235 (0.7%) is fissile and can be used to generate electricity in a nuclear power station.
The mix is transformed and enriched in order to increase its uranium 235 content. The result is enriched uranium, containing 3 to 5% uranium 235, which is used to produce the actual nuclear fuel.
