Attaining fundamental understanding of fuel performance requires detailed characterization of irradiated fuels under variety of irradiation conditions. In order to improve the overall viability of MOX fuels, it is necessary to develop a comprehensive knowledge of the fuel evolution and the effects on the macroscale properties. The objective of the proposed research is to utilize advanced characterization techniques to conduct detailed microstructural examination of the next in a series of available MOX fuel burnups. The microstructure of high burn-up mixed oxide fuel with local burn-up of 6.7% fissions per initial metal atom (FIMA) will be examined. Characterization will focus on understanding the effects of radial position on the fuel pellet, which will be focused on documenting the effects of irradiation conditions on the local microstructure of the fuel. The proposal will conduct microstructural characterization of the fuel using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to observe grain morphology, fission product distribution, and dislocation densities, among other features.

Technical relevance of the proposal is directly related to the Department of Energy Office of Nuclear Energies mission to advance nuclear power as a resource capable of meeting the nation’s energy, environmental, and national security needs, and the mission to develop next-generation advanced nuclear fuels. The proposed project will benefit the Fuel Cycle Technology (FCT) program, funded by DOE NE and Advanced Fuel Cycle Initiative. The detailed investigation proposed in this project is aimed towards obtaining experimental results for critical first step in understanding of the fuel performance throughout life, mechanisms of HBS formation, and the effects of irradiation conditions on the local microstructure of the oxide fuel. The results will provide critical input for ongoing modeling efforts conducted through NEAMS program at INL. The experimental data will provide direct benchmarking of the MARMOT code by evaluating the fidelity of physics, materials science principles and models, and the coupling of multi-physics solutions. The three dimensional structure of irradiated fuels is largely unknown, which is a limiting factor for being able to accurately model the thermal behavior of the fuel. Therefore, the data obtained through this proposal will provide valuable input to ongoing modeling efforts on irradiated fuels. The project is going to take a critical step towards determining the fundamental fuel performance characteristics of mixed oxide fuel.