The coprecipitation and conversion of mixed actinide oxalates for aqueous-based reprocessing of spent nuclear fuels

Oxidation as an Early Stage in the Multistep Thermal Decomposition of Uranium(IV) Oxalate into U3O8

“…Finally, it is also involved in the reprocessing scheme of composite (Th, 233 U)O 2 -(Th,Pu)O 2 fuels planned to be used in advanced heavy water reactors (AHWR) 8,9 . In all these examples, the selectivity of the oxalic precipitation for some actinides, according to the conditions of precipitation, enables an additional level of control on the nature of the metal cation present in the oxide 10,11 .…”

“…8,9 In all of these examples, the selectivity of the oxalic precipitation for some actinides, according to the conditions of precipitation, enables an additional level of control on the nature of the metal cation present in the oxide. 10,11 Thermal decomposition of metal oxalates was studied for decades, leading to several reactive pathways proposed in the literature. 12−16 Nevertheless, none of these mechanisms could properly summarize the numerous specificities observed, such as the presence of different carbonates and oxo-carbonates intermediates, or the finely divided state of a metal at the end of the reaction leading to pyrophoric effect.…”

“…As such, plutonium­(IV) is currently precipitated as Pu­(C 2 O 4 ) 2 ·6H 2 O in the back end of the French PUREX partitioning process, then calcined into PuO 2 to further refabricate fresh (U,Pu)­O 2 MOx fuels . Oxalic route is also envisaged in order to operate the coprecipitation of uranium, plutonium and/or minor actinides, with the aim to prepare advanced fuels for fast-neutron reactors. , Finally, it is also involved in the reprocessing scheme of composite (Th, 233 U)­O 2 -(Th,Pu)­O 2 fuels planned to be used in advanced heavy water reactors (AHWRs). , In all of these examples, the selectivity of the oxalic precipitation for some actinides, according to the conditions of precipitation, enables an additional level of control on the nature of the metal cation present in the oxide. , …”

From Nd(III) and Pu(III) Oxalates to Oxides: Influence of Nitrilotris(methylenephosphonic acid) on Chemical Composition, Structure, and Morphology

“…Oxalic conversion is a well-known process to obtain metal oxide from cations in solution. − In the nuclear field, the recovery of valuable actinides requires, first, to dissolve the spent fuel, then to partition the elements, and finally to recover the valuable actinides into a solid form by means of a conversion step that can be achieved by oxalic precipitation. This process leads to the precipitation of solid actinide oxalates used as oxide precursors .…”