In France, nuclear power plants generates approximately 68% of the country’s electricity, with a very low carbon footprint. However, it produces various types of radioactive waste throughout its life cycle, including so-called high-level waste resulting from spent fuel reprocessing. These wastes are confined within a borosilicate glass matrix whose structure allows for the incorporation of a large number of chemical elements at the atomic level, ensuring excellent long-term performance properties. Future challenges facing the industry may lead to changes in nuclear fuels and their burn-up rates, as well as adaptations to processing and recycling methods, which could alter the nature and chemical composition of waste solutions intended for vitrification.
Among these elements, gadolinium (Gd) — used as a neutron absorber in nuclear fuels — is of particular interest due to its complex behavior in solid solution and its potential to form crystalline phases (e.g., silicate apatites) when interacting with other rare earth elements (La, Nd) or actinides (Am). These crystalline phases could profoundly alter the structure of the glassy matrix and affect the material’s properties (chemical durability, radiation resistance. This thesis therefore aims to understand and quantify the synergistic effects between gadolinium and other rare earth elements in simplified borosilicate glasses, in order to better understand the crystallization affinities among the various elements. It will thus enable the identification of the nature, structure, size, and concentration of the various phases that may form. Their structural changes induced by alpha irradiation will also be studied to simulate the effects of actinides, particularly the swelling of crystalline phases and its impact on the material.
The PhD student will benefit from the recognised skills of the host laboratory in glass formulation as well as the study of their physico-chemical properties. All of the resources made available will enable a global approach to the subject, working on a fast-growing topic with major industrial and societal implications. The experience acquired during this interdisciplinary work will be useful in the field of materials.