Dissolution in nitric acid is a key step in the recycling of spent nuclear fuels. In the case of MOx fuels (U,Pu)O2, it generates complex solid residues containing potentially recoverable actinides and fission products, some of which are critical metals of strategic interest for technologies such as semiconductors, photovoltaics, and fuel cells. A second oxidative dissolution step is currently being investigated to enable their recovery. However, the nature and physicochemical properties of these residues remain difficult to study due to their high radioactivity and limited availability.
The objective of this PhD thesis is to establish and validate a methodology for developing surrogate materials representative of the residues generated during the dissolution of MOx fuels.
The first step will consist of reviewing the literature to establish a comprehensive overview of the main physicochemical characteristics of actual residues, including their composition, particle size, and the nature and structure of the phases present, as well as the oxidation states of the cations. Dissolution experiments on simulated MOx fuels (simMOx) will then be carried out to produce residues that can be characterized using techniques that are difficult to apply to irradiated materials. These results will be used to define the properties to be reproduced when developing the surrogate materials. Their representativeness will be assessed by comparison with actual residues and those obtained from the dissolution of simMOx. Finally, their behavior during oxidative dissolution will be compared with that of actual residues and simMOx-derived residues, in order to validate their relevance as experimental model materials.
At the end of the PhD, the candidate will have acquired strong expertise in the study of complex systems, the physicochemical characterization of materials, and the critical analysis of literature and experimental data. This multidisciplinary training will open up a wide range of career opportunities in academic research and industrial R&D, both within and beyond the nuclear sector.