Radiological Safety Training for Uranium Facilities
Module 102 The Nuclear Fuel Cycle
At this stage in the nuclear fuel cycle, the yellowcake is converted into uranium
hexafluoride (UF6) for enrichment. This is accomplished by:
Conversion of yellowcake to pure uranium trioxide (UO3), called "orange
oxide" or "orange salt," by solvent extraction and follow-up drying.
Conversion of UO3 to uranium dioxide UO2.
Conversion of UO2 to uranium tetrafluoride (UF4) by hydrofluorination
(addition of hydrogen fluoride gas). This product is called "green salt."
Reacting the UF4 with fluorine gas (F2) to form uranium hexafluoride
(UF6), which is a volatile form ready for enrichment. The UF6 is a solid at
room temperature but readily becomes a gas when heated above 56°C.
The enrichment process is necessary to increase the percentage of the 235U
isotope in the uranium to make it suitable for reactor fuel. Natural uranium
contains 0.7%235U. Typically, enriched uranium contains 2-4% 235U. Other
uses may require much higher concentrations up to, or even greater than, 90%
235U. Depleted uranium, which is left over after the enrichment process, has an
abundance of about 0.2% 235U.