Understanding thermodynamics, (local) structure and electronic evolution of uranium-bearing solids under reactive or extreme environments is essential for predicting their behavior in nuclear fuel cycles. In this talk, I will discuss the use of calorimetry, X-ray absorption spectroscopy and related techniques, and first-principle calculations on probing chemistry and stability of two uranium solid-state systems: UO2 and USiO4. Two case studies will be covered.
First, lanthanide (Ln)-incorporated UO₂ solid solutions were examined as analogues for mixed-oxide and spent nuclear fuels. XAS provides insight into how Ln substitution perturbs the uranium oxidation state and local lattice environment, offering mechanistic understanding of f-element binary (or multi-component) mixing systems that are relevant to long-term fuel evolution. In the second case, USiO4 (coffinite), and its isostructural zircon-type solid solutions (uranothorite, and chernobylite) are studied for thermodynamic stability. This is related to respository application and disaster site assessment.
