Doctoral Preliminary Oral Defense – Shinhyo Bang

About the event

Speaker:  Shinhyo (James) Bang

Group:  Professor Guo

Title:  A Study on the Impact of Dopants on Uranium Dioxide Degradation

Abstract:  This proposal aims to explore the effects of dopants on UO2, its degradation products, and a final immobilized waste form of U, from structural and thermodynamic perspectives. The outcomes of my project will be fundamentally important in understanding the degradation processes of spent nuclear fuel (SNF). Specifically, my work will focus on the thermal oxidation of Zr-doped UO2 (for dry-storage of SNF) and the high-pressure phases of U-Th orothosilicate, uranothorite (relevant for SNF degradation phase and ceramic waste form for deep geological repository). In situ high temperature x-ray diffraction (XRD) of Zr-doped UO2 has revealed the segregation of multiple phases including monoclinic ZrO2 from higher U oxide phases and dissolution into U3O8. In situ Raman spectroscopy and XRD of U-doped ZrO2 provide crucial insights into the intermediate phases formed during oxidation. High-temperature oxide solution calorimetry on Zr-doped UO2 and U3O8 is planned to experimentally determine the thermodynamic mixing models for binary systems identified in the U-Zr-O diagram. In situ high pressure XRD and Raman experiments have revealed the pressure-dependent properties of uranothorites, namely the bulk moduli, anisotropic parameter, and Grüneisen parameters. XRD has indicated a puzzling phase stability in U-rich uranothorite similar to that of thorite instead of coffinite, despite uranothorite, thorite, and coffinite are all isostructural. To address this anomaly, a hypothesis of nanosized heterogeneity will be examined by high-resolution transmission electron microscopy (HRTEM). Furthermore, the Gibbs free energy of formation at the high pressure will be calculated based on current thermodynamic parameters.