Advances in Measurements of the Melting Transition in Non-Stoichiometric UO2

This work presents a study of the melting behavior of the UO2+x system. Self-crucible pulsed-laser melting at high pressure is realized, further improving the recently developed experimental approach. Thermograms of the heated surface of the sample, recorded by a fast pyrometer, show thermal arrests and/or points of inflection corresponding to the phase transformations. A further probe laser beam is focused onto and reflected by the sample surface, and the reflected light intensity is used to detect the exact instants at which melting/freezing transitions occur. Furthermore, a model was developed describing the complex process of laser-induced melting in a system where a solubility gap accompanies the formation of liquid, and a corresponding numerical simulation of the melting-freezing process was performed in order to depict the heat and matter transport phenomena involved. Finally, liquidus and solidus lines are proposed for the system UO2+x in the range 0≤x≤0.21.