XAS Study of homogeneous (U,Nd)O2 solid solutions vs temperature and firing conditions

The study of the prevailing factors impacting the dissolution kinetics of UO2-based compounds is of primary importance to forecast the behavior of the SNF during its reprocessing. Using Nd as surrogate for minor actinides and fission products, our goal is to study the impact of the U speciation and O vacancy formation on the dissolution kinetics and mechanisms of U1-yNdyO2-x solid solutions. Our first results revealed a much lower chemical durability of U1-yNdyO2-x samples compared to UO2. A 100-fold increase in dissolution rate was found between samples prepared at 700 and 1200°C suggesting important differences in U valence states and O vacancies concentrations. In this aim, HEFRD-XANES measurements will provide us crucial information on the U speciation in the prepared solids (various temperatures and operating atmospheres), especially in terms of U(IV)/U(V) ratio. In the meantime, the analysis of U and Nd environments by EXAFS will allow us to confirm the presence of O vacancies.