CEA Valduc operates processes involving molten salts. These salts, based on chloride compounds, can exhibit corrosive properties, particularly in the presence of impurities that lead to oxygen contamination. This results in the degradation of materials used in these processes. The study proposed here aims to understand these degradation mechanisms in order to identify the materials that best meet the needs of CEA Valduc. Beyond the specific requirements of CEA Valduc, this study also fits more broadly within ongoing research efforts to understand and mitigate corrosion in high-temperature molten salts environments, a major technological challenge for advanced modular reactors (AMRs).
The proposed work aims to study and compare various refractory materials in contact with chloride salts. Oxide materials (MgO, Y2O3, Ta2O5) and carbides (TaC) will be investigated in contact with CaCl2, NaCl, and KCl salts. The solubility of these materials in different molten salt media will be measured. The ultimate goal is to evaluate the behavior of these materials under aggressive conditions and to understand the mechanisms of their degradation.
Several studies have highlighted the predominant role of the material microstructure in relation to chemical durability. Initial characterization of the materials will be carried out using the facilities of Institute Jean Lamour (SEM/TEM, XRD). A thermodynamic study using the FactSage software will also be performed to predict material behavior and possible chemical reactions. The core of the thesis will consist of corrosion tests. Solubility constants of these different materials in chloride salts will be measured, followed by an investigation of phenomena occurring at the salt/material interface on sintered samples. Literature underscores the crucial influence of oxygen content on the corrosive nature of molten salts. Precise control and in situ measurement of oxygen levels is therefore critical for this work. To this end, the PhD candidate will have access to CEA’s facilities that enable work under inert atmosphere and analytical electrochemical measurements. Post-corrosion elemental analyses (ICP-AES/MS, UV-Vis spectroscopy) of the salts will be combined with microstructural characterizations of the samples to propose corrosion mechanisms for each material.
All experiments will take place at the CEA Valduc site, with occasional travel required to the IJL facilities in Nancy.