SimFuels are synthetic UO2 materials that contain specific radionuclides or non-radioactive analogs that can be used to conduct research in the absence of irradiated fuel like spent nuclear fuel (SNF). For this research, uranium oxide pellets are pressed and doped with cesium and iodide and heat-treated under various stimuli to examine the chemical behavior of the defects with respect to the uranium oxide chemistry. Cesium-137 is a high-yielding, high-energy gamma emitter with a half-life of about 30 years, often present as a mixed oxide or dissolved inside the [U,Pu] fuel matrix, while Ioide-131 is a short-lived, high yielding fission gas. We hypothesize the possibility of CsI forming in spent fuel in small quantities, and while there hasn’t been any physical proof of CsI in spent fuel, this research aims at providing evidence that CsI can exist in the fuel matrix. The UO2 pellets are pressed with various concentrations of CsI and heated under various stimuli, including high temperatures and in different atmospheres. We further reduce the concentration of CsI to try to mimic SNF to the best of our ability. Another important aspect of this research is the use of density functional theory (DFT) to help validate experimental findings. DFT has confirmed that CsI is stable in a UO2 matrix, but this doesn’t explain how it can be formed. Further analysis is required, but the data collected so far, both experimentally and via DFT, are going to be used to help support a machine learning program we are creating that utilizes Bayesian probability, where the goal of the program is to provide a probability to a hypothesis given prior probabilities, i.e., those gathered from experiment and theory.

High-temperature reactions of simulated uranium oxide pellets doped with cesium and iodide matrices

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ACS Fall 2022

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