The conversion from uranium oxide to UF₆ proceeds in two main chemical steps:
Step 1: Production of UF₄ (uranium tetrafluoride)
Uranium oxide powder is reacted with anhydrous hydrofluoric acid (HF) at approximately 450 degrees C in a rotary kiln. This produces the intermediate compound UF₄, a green powder sometimes called “green salt.”
Step 2: Production of UF₆ (uranium hexafluoride)
UF₄ powder is then reacted with elemental fluorine gas (F₂) in a fluidised bed reactor. This exothermic reaction produces gaseous UF₆, which is cooled and collected as a solid in steel containers.
Industrial Note: The Pierrelatte facility in France experienced a release of 7 tonnes of hex on 1 July 1977, but this did not lead to a major off-site hazard due to the relatively low radioactivity of hex at natural enrichment.