In the rare event of nuclear reactor core meltdown, uranium dioxide fuel reacts with its Zircaloy cladding to produce eutectic melts which can subsequently be oxidized by coolant water. Understanding the atomic interactions at these extreme conditions to help improve reactor safety and design accident-tolerant fuels poses many experimental challenges. Here we use aerodynamic levitation combined with laser heating to enable experiments on ceramics at high temperatures in excess of 3000 degrees Kelvin, eliminating the possibility of contamination with a furnace container. High energy x-ray diffraction provides a direct probe into the atomic structure and local disorder within materials, that can be directly compared to molecular dynamics simulations. Together these tools provide a powerful insight into structural interactions at the atomic level that are responsible for a material's macroscopic behavior, and the relation to properties such as thermal expansion, density and viscosity. Examples of high temperature crystallography on uranium dioxide, liquid state structure measurements using pair distribution function analysis, as well as deviations from stoichiometry at high temperatures will be discussed. I will also present studies on atomic scale interactions in corium, the so-called Chernobyl “lavas”, that form when the molten fuel and its cladding material combine during core meltdown, which are important for modeling severe accident studies.
Argonne Physics Division Colloquium Schedule