Résumé
Highly focused research programs on nuclear waste vitrification are still underway in the CEA. The main issues facing us today are to accommodate new types of wastes and increase waste loading, while enhancing the glass quality and increasing the production capacity and robustness of plants. This requires an extensive knowledge on glass melting processes and physicochemical of vitreous materials. Fundamental research supported by a modelling approaches together with experiments are conducted from laboratory-scale and mock-up, to full-scale non-radioactive facilities. The latest developments on the chemical mechanisms that can occur at high temperature during vitrification, such as denitration, crystallization, demixing, and dissolution, together with the associated thermodynamic and kinetic parameters (activation energy for denitration, dissolution, crystallization), will be presented in this talk. An insight on the influence of the microstructure (nature of crystalline and separated phases – fig.1) and morphology (polyhedral, dendritic, and spherical) on the physicochemical properties, specifically on viscosity and electrical conductivity, of the molten glass will be also done. In the last section, we will focus on Magneto-Thermo-Hydraulic (MTH) simulation, improved by taking into account the chemical, thermal, and rheological laws and relevant parameters to predict the vitrification of uranium oxide-type waste. Simulation case will be given for simple and more complex crucible geometries.