Structural approach of molten fluorides of nuclear interest: NMR and EXAFS at high temperature

摘要

Our objective is to describe the local structure of molten fluoride mixtures involved in Molten Salts Reactors, or in the pyrochemical treatment of spent nuclear fuels. We use an experimental approach combining twospectroscopy both sensitive to the microstructure of solid or liquid materials: NMR for the light cations (~(27)Al, ~(23)Na,~7Li) and anions (~(19)F, ~(17)O) and EXAFS for the heaviest such as rare earths, La, Y, Nd, and actinides, Thorium andUranium nuclei. The knowledge of the different species existing in the melt, and their proportions depending onthe composition and the temperature is of major importance for a better understanding of the properties of moltenfluoride mixtures. Because of their strong reactivity at high temperature (up to 1500°C for fluorides) towards a great number of materials, the experimental analysis of molten fluorides is extremely difficult and requires specific developments.