The dissolution of spent nuclear fuel is an essential first step in its reprocessing. The kinetics of irradiated (U,Pu)O2 (MOX) dissolution currently hinders industrial-scale reprocessing and therefore requires a better understanding of the mechanisms involved in order to overcome this industrial obstacle. However, studying the dissolution of irradiated MOX fuel in order to identify and model the various stages and mechanisms involved is hampered by the high radiotoxicity of such material and the representativeness of the available samples. In order to simplify these studies and establish representative models, numerous tests have been carried out on model compounds (e.g., non-irradiated UO2 and MOX). Among these, SIMfuel (U,Pu)O2 compounds doped with up to 11 fission products aim to represent the chemical complexity of irradiated fuels. The conventional approach to manufacturing SIMfuel by mixing solid-phase reagents requires sintering of fuel pellets at high temperatures (>1600°C). In order to reproduce the behavior of fission products (reduction-oxidation, distribution, etc.) for irradiated fuels at lower temperatures, an alternative approach has been developed based on the synthesis of oxides via the hydroxide route. This method allows for the simultaneous and homogeneous precipitation of numerous metal cations and significantly lowers the sintering temperature. This approach has already enabled the study of SIMfuel incorporating rare earths, platinoids, and molybdenum under representative conditions. However, this approach has never been implemented for the synthesis of SIMfuel containing both plutonium and all fission products relevant to the study of dissolution.
The objective of this thesis is to implement such syntheses, based on recent results obtained concerning the synthesis of MOx by the hydroxide route. To this end, SIMfuels will be synthesized to represent spent MOx-type fuels (SIMMOx). To represent the different zones present in spent fuel, SIMMOx with different Pu/(U+Pu) ratios will be considered. These SIMMOx will undergo dissolution tests to characterize their behavior during this stage.