The ore extracted from the mine is often quite low in grade. Uranium from these ores must therefore be concentrated. How? The rocks are crushed and then finely ground and the uranium extracted through a number of chemical operations. This is referred to as processing, and the result is a yellow paste known as “yellow cake”, which contains 75% of uranium oxide.
The “yellow cake” is then purified by a series of chemical transformations and converted into a fluorinated form (UF6: 6 fluorine atoms for one uranium atom). This is called the “conversion” operation. Now free of impurities, the uranium can pass to the next stage: enrichment. In order to fuel nuclear reactors and produce electricity, the natural uranium must be enriched with a higher proportion of uranium-235. The 0.7% of uranium-235 content present in the natural uranium is concentrated to obtain a 3 to 5% content, i.e. 7 times more than that found in “yellow cake”.