A depleted UF.sub.6 processing plant including a first fluidized bed reactor configured to react depleted UF.sub.6 with steam to produce UO.sub.2F.sub.2 and hydrogen fluoride, a second fluidized bed reactor connected to the first fluidized bed reactor and configured to react the UO.sub.2F.sub.2 with steam to produce U.sub.3O.sub.8, hydrogen fluoride and oxygen, a gas cooler configured to cool the hydrogen fluoride generated in the first and second fluidized bed reactors down to 150 to 300.degree. C., and a fluorine fixing reactor containing granular calcium carbonate and connected to the gas cooler to receive the hydrogen fluoride cooled down to 150 to 300.degree. C. from the gas cooler. The fluorine fixing reactor is configured to form granular calcium fluoride from the granular calcium carbonate and the hydrogen fluoride passing through the fluorine fixing reactor.