Reprocessed uranium (RepU), derived from the reprocessing of spent nuclear fuel, represents a material whose reuse in power plants would allow for the sustainable management of energy resources. Accordingly, the CEA is supporting the nuclear industry to evaluate the feasibility of enriching this RU via the laser route. This technology requires, as a process input, uranium in the form of a metallic alloy. Consequently, an upstream process for the synthesis of metallic uranium must be developed and optimized to build a sovereign RepU sector.
One of the routes under study for synthesizing metallic uranium is the electrolysis of uranium oxide, previously dissolved in high-temperature molten fluoride salt media. This synthesis, which was previously implemented in the United States using the aluminum synthesis process, now requires a re-appropriation and optimization of experimental conditions.
In a first phase, the PhD student will conduct a systematic study of the electrolyte, in order to understand the influence of key parameters—salt composition, temperature range, redox environment, material compatibility, and oxide solubility—on the behavior of the electrolysis bath. For each parameter, targeted tests will be conducted: thermochemical characterization of the salt (melting point, volatility, purification, etc.), evaluations of the kinetics and the solubility limit of uranium oxide in the bath (a crucial point of the process), electrochemical tests aimed at identifying redox systems of interest, as well as studies on the resistance of materials when in contact with the molten salt and liquid metal. All of these investigations will make it possible to define the optimal experimental conditions for the controlled implementation of metal synthesis by oxide electrolysis.
In a second phase, once these conditions are established, the work will focus on the formation of the metal at the electrode, its recovery, and its characterization. The quantity and quality of the metal produced after electrolysis will be the major criteria for validating the selected experimental parameters.
All acquired data will be utilized for the design of pilot and industrial scale electrolyzers, and will feed into future digital models that will be developed. The results obtained may be the subject of presentations at international conferences and publications.
These studies will be carried out at the laboratory scale using active material, with work phases on simulants to grasp the implementation of the process and scaling up. The host laboratory, which operates in both these environments, specializes in the implementation of thermal processes and pyrochemical tests.
The candidate should ideally have a Master 2 or engineering school degree in chemistry or physics.
At the end of this thesis work, the PhD student will have acquired expertise in experimental techniques related to metallic synthesis by electrolysis, from the design of electrochemical devices to the multi-scale characterization of materials. Furthermore, their involvement in a sovereign project focused on strategic metals will open up numerous employment prospects in academic research or industrial R&D, both in the nuclear sector and in other fields of chemistry and materials.