The further processing of the uranyl nitrate solution, which in some plants is postpurified with silica gel, is directed towards further enrichment of the uranium. If this is not worthwhile due to a too low ²³⁵U-content, the product is converted into uranium(Ⅵ) oxide, a storable compound. This can serve as a starting material for possible later utilization in fast breeder reactors. The uranium(Ⅵ) oxide is either produced indirectly by way of ammonium diuranate or by direct calcination. If further enrichment is foreseen, uranium(Ⅵ) fluoride or uranium(Ⅳ) fluoride is produced, the latter being fluorinated in the enrichment plant to uranium(Ⅵ) fluoride.

Plutonium is usually precipitated in reprocessing plants as its oxalate, which is converted into plutonium(Ⅳ) oxide from which mixed oxide fuel elements for light-water reactors or fast breeder reactors can be manufactured. Considerable knowledge over the manufacture of mixed oxide fuel elements has been built up over the years in the USA, France, Great Britain, Japan, Belgium and the Federal Republic of Germany. Thus up to the end of 1993, just in the Federal Republic of Germany, 4.5t of fissile plutonium had been incorporated into more than 100,000 fuel rods, mainly for utilization in light-water reactors. The 26,000 fuel rods destined for use in the fast breeder reactor at Kalkar, have not been able to be used.