The uranates and uranyl nitrate from the milling plants are transferred to a refining and conversion facility. This installation also receives other forms of uranium, notably U308.

In this installation, the level of impurities is reduced-- to 0.02% as of 1996. This is the stage of purification or refining.

Then, the purified product is transformed into uranium tetrafluoride (UF4, green salts). The UF4 can serve as a base for the production of either uranium metal or uranium hexafluoride (UF6). In France in the past, a part of the UF4 was converted to uranium metal for UNGG fuel. Today all the UF4 is converted to UF6 in preparation for enrichment.

The procedure consists of the following stages:

We present the wet process, which is generally used:

Dissolution in concentrated nitric acid of the solid uranium materials received at the plant. The liquid obtained is impure uranyl nitrate. If necessary, the uranyl nitrate is filtered during this stage.

Purification of the uranyl nitrate from stage one and of the uranyl nitrate received in that form, "by liquid-liquid exchange between the water-based uranyl nitrate solution and a solution of tributylphosphate (TBP) in dodecane." The liquid obtained is pure uranyl nitrate, which is then evaporated to increase the concentration.

The precipitation of uranyl nitrate by gaseous ammonia. The product obtained is ammonium diuranate (DUA).

The calcination of ammonium diuranate, around 400 degrees Centigrade, to produce UO3.

The reduction of UO3 by hydrogen, obtained thermally by cracking ammonia gas (NH3). The product obtained is UO2.

The hydrofluorination of UO2 by hydrofluoric acid (HF) in a furnace to produce UF4.

UF4 was converted to uranium metal by calciothermic or by magnesiothermic reduction. The UF4 and metallic calcium or magnesium were loaded into a bell jar. In the reaction that followed, under a vacuum and at a high temperature, the uranium melted and came together in a crucible. The byproduct was calcium or magnesium fluoride, sometimes ground and reused, sometimes sold, and sometimes disposed of as a waste.

UF4 is transformed into UF6 by fluorination in a flame reactor. The reactor is composed of a long vertical tube in which solid UF4 spontaneously bursts into flame on contact with gaseous fluorine. The gaseous UF6 is cooled in crystallizers and then liquified and let flow by gravity and under pressure into transport containers. It is allowed to crystallize in the container for storage and transportation.

The Comurhex plant at Malvési carries out the conversion of concentrates to UF4 and has carried out the conversion of UF4 to metal. The Comurhex factory at Pierrelatte converts UF4 into UF6. The Centre du Bouchet, which no longer exists, converted concentrates into metal and into UF4.

To convert the uranyl nitrate that is a product of reprocessing, into UO2 or UF4, the conversion process used at Malvési can be employed, beginning with the stage of precipitation by means of ammonia to obtain ammonia diuranate. Comurhex treated the Repu uranyl nitrate at Malvési by adding it to the solution produced by the dissolution of uranates in nitric acid [BIST ii.64]. The Ateliers pilotes (pilot workshops) of Comurhex at Pierrelatte produce UF4 by the method used at Malvési.

The procedure for transforming uranyl nitrate into U308 then UO2 can be adapted by changing the conditions of calcination. The TU2 workshop of Cogéma at Pierrelatte produces U308 by carrying out the calcination of ammonium diuranate at 700 degrees Centigrade under air and then obtains UO2 by reduction of U308 in a furnace at between 650 and 700 degrees Centigrade in the presence of hydrogen.

Cogéma’s TU5 workshop at Pierrelatte produces UF4 and U308 by other processes (see TU5 under Pierrelatte).

The conversion of UF4 to UF6 is carried out by fluorination in a flame reactor. This stage is a stage of partial purification. A major part of the transuranians and fission products remain in the wastes. Comurhex uses a distinct installation for the uranium from reprocessing, the Ateliers pilotes at Pierrelatte.