In Situ X-Ray Absorption Spectroscopy Study of Radiolysis-Induced Redox in Chromium Nitrate Aqueous Solution Under Supercritical Condition

Abstract

The radiolysis-induced redox in a chromium aqueous solution was observed based on synchrotron X-ray absorption spectroscopy (XAS) measurements. The in situ Cr K-edge XAS spectra were acquired for a chromium nitrate aqueous solution with the concentration of Cr(III) at 1000 ppm from room temperature up to 500oC. The radiolysis in such a fluid sample within a specifically designed hydrothermal diamond anvil cell (HDAC) caused the oxidation of Cr(III) to Cr(VI) at temperature above 300oC, and the reduction of Cr(VI) to Cr(III) at 500oC. The two components of the pre-edge peaks of the K-edge spectra were fitted using an established fitting model (tetrahedral and octahedral) and applied to identify the presence of Cr(VI) in the solution. The influence of the high basicity ligand, i.e. Cl-, on the electronic environment of the Cr center is also discussed. Knowledge of the local structure of Cr aqua ions under conditions of extreme temperature and radiation is important for understanding of corrosion product transport in advanced nuclear reactors.