Characterization of phases of interest for corium : chernobylite and oxide based solid solutions

During severe nuclear accident, the loss of cooling leads to HT reactions between UO2 and surrounding materials, forming corium and containing Zr1-xUxO2 phase. When contact with concrete, it can produce chernobylite (Zr1-xUxSiO4). To fill the poor knowledge of U-Zr-O and UO2-ZrO2-SiO2 systems, an international collaboration has been launched to prepare and characterize both phases through advanced structural analyses and thermodynamic measurements. The aim of the proposal is to understand the formation conditions, incorporation limits and thermal stability of both Zr1 xUxSiO4 and Zr1-xUxO2, to finally predict phases formed in the corium. HR-PXRD analyses will allow a finer structural characterization of the solid solutions whereas HERFD-XANES and EXAFS analyses of chernobylite will allow the analysis of U-speciation in the zircon structure. Those characterizations will be of prime interest in linking this approach to solubility experiments and thermodynamic data determinations.