FROM NATURAL URANIUM TO URANIUM HEXAFLUORIDE (UF6)

The uranium extracted from mines, concentrated in the form of "yellow cake" and already under the ownership of the electricity customer, cannot be used in this state in nuclear reactors. To be used as a fuel, it must be transformed.
The conversion operations consist of transforming the concentrated ores into uranium hexafluoride (UF6), giving it the purity needed for the fabrication of nuclear fuel.
These operations represent an essential stage in the fuel cycle between mining activities and enrichment of the uranium.
A 2-STAGE PROCESS
The conversion of uranium concentrate obtained from mines is carried out through a process of chemical transformation in 2 stages:
Transformation of natural uranium into uranium tetrafluoride
During the first phase, the uranium is transformed into uranium tetrafluoride (UF4).
The concentrated ore is dissolved by acid, then purified to yield. This generates effluents, treated on site. After precipitation and calcination, uranium trioxide powder (UO3) is obtained, and is thenhydrofluorated using hydrofluoric acid.
It is thus transformed into a green substance with a granular appearance called uranium tetrafluoride (UF4).
These operations are carried out in the COMURHEX-Malvési plant in Narbonne, France.
Transformation of uranium tetrafluoride into uranium hexafluoride
The UF4 is then converted in a second phase of fluorination into uranium hexafluoride (UF6), using fluorine obtained by electrolysis of hydrofluoric acid. Slight changes in temperature cause UF6 to change from a solid state to a gaseous state. At 65 °C, UF6 takes on a gaseous form. It is then ready for enrichment.
These operations are carried out in the COMURHEX plant in Tricastin.

Fuente: http://www.areva.com/EN/operations-757/conversion-the-fluorination-of-uranium-in-2-stages.html