Time-resolved structural and chemical investigations of metal oxide - water systems under conditions of extreme temperature, pressure and radiation

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In situ x-ray and Raman spectroscopic techniques will be used to directly probe the structure and composition of selected metal oxide-water systems in hydrothermal diamond anvil cells at conditions of extreme temperature (300-700 degrees C), pressure, and radiation. The proposed experiments will address three important questions pertaining to corrosion and corrosion product transport in supercritical water cooled reactors. These are: (1) What is the solubility of chromium(III) oxide (eskolaite) in hydrogen peroxide-bearing supercritical water? (2) How might metal oxide nanoparticles participate in corrosion product transport? And, (3) What is the effect of irradiation on the structure and stability of aqueous transition metal complexes in supercritical water? Time-resolved, energy-dispersive x-ray absorption spectroscopy (ED-XAS) will be used in this study for the first time to monitor (with microsecond resolution) the effects of synchrotron x-ray induced radiolysis on the local structure and valence state of transition metal ions in supercritical water. X-ray absorption spectroscopy will also be used to investigate the reaction between Cr and Fe nanoparticles and transition metal aqua ions in supercritical water. Synchrotron x-ray fluorescence spectroscopy (SXRF) will be used to directly determine the composition of fluids at elevated temperatures and pressures in the hydrothermal diamond anvil cell. The anticipated results will significantly advance our understanding of the interaction of aqueous fluids with candidate materials and the transport of corrosion products in aqueous fluids at conditions relevant to GEN IV operating conditions. The research will also provide new thermochemical data for a database that is needed to quantitatively predict and control water chemistry in order to minimize material degradation and corrosion product transport at high temperatures.