Development and characterization of a new matrix for immobilizing lead and lead-bismuth waste stream

The advancement of the nuclear industry drives the development of new reactor designs focused on improved safety, efficiency, and sustainability. Among the new designs under evaluation, this study focuses on lead-alloy cooled fast reactors, which use lead or leadbismuth as a coolant. The advantage of using this type of coolant is that it can operate at very high temperatures while maintaining single-phase cooling under normal pressure. The development of this new type of reactor generates a new category of nuclear waste, which sustainable management is a major environmental challenge. This thesis aims to propose an alternative to the use of Ordinary Portland Cement (OPC) as a waste immobilization matrix. Indeed, the use of this type of cemented matrix is the most common immobilization technique, but has the disadvantage of producing a significant amount of carbon dioxide. The aim of this thesis is therefore to develop and characterize a new immobilization matrix containing vitrified bauxite residues (VBR) as a partial replacement for OPC. To do so, two Fe-rich matrix formulations, containing 20 wt.% and 17 wt.% VBR respectively, were studied. Their rheological behavior, mechanical properties, and chemical stability were analyzed and compared to those of a reference mortar. Next, the characteristics of the lead and lead bismuth waste to be incorporated into the matrix were studied. Finally, lead and lead-bismuth waste was also incorporated into these matrices to evaluate the interaction between the waste and the matrix. This has demonstrated that the iron-enriched matrices investigated in this thesis offer numerous advantages for the immobilization of lead and lead-bismuth waste. The addition of VBR resulted in improved mechanical properties, higher viscosity, and better resistance to leaching. However, waste corrosion remains a major problem, preventing effective long-term immobilization of the waste.