Developing Microstructurally Accurate Finite Element Meshes for Nuclear Fuels from 3D FIB Tomography Data

Generation IV reactor designs are exploring fuel designs beyond conventional uranium dioxide (UO2), which will require extensive experimental and computational efforts to ensure the fuel is qualified for commercial use. Unlike UO2, empirical models are not feasible due to the lack of extensive commercial operating data. Given this limitation, recent efforts have focused on developing multi-scale mechanistic fuel performance models, utilizing underlying physics and microstructural knowledge of the fuel system rather than empirical correlations to predict fuel performance. These models, while offering greater flexibility in fuel performance modeling, will likely face challenges during licensing activities regarding how the simulated microstructure used in the models can be experimentally validated. Creating concrete connections to bridge the gap between mechanistic models and experimental data is crucial to the success of mechanistic approaches in fuel performance modeling. This study seeks to address this gap by developing finite element meshes of an irradiated mixed oxide (MOX) fuel microstructure obtained directly from 3D focused ion beam (FIB) tomography data. The data consists of backscatter electron (BSE) micrographs captured between consecutive FIB millings of a 24.6 µm x 17.8 µm x 26.2 µm MOX cube lifted out from an irradiated fuel pin, as shown in Figure 1. Electron backscatter diffraction (EBSD) and energy dispersive x-ray spectroscopy (EDS) were collected alongside the BSE data to inform grain orientation and chemical distribution, respectively. To reconstruct the pore structure in three dimensions, image segmentation using the morphological active contours without edges method is applied to separate pores from the fuel matrix. Fast Fourier Transform (FFT) filtering is used to mitigate curtaining artifacts that arise during FIB milling. Data between image slices is generated using second-order spline interpolation to create a continuous 3D volume that captures pore morphology (see Figure 1). EBSD and EDS data is then used to develop the microstructure of the fuel matrix. Mesh generation techniques are then used to create a model for finite element analysis (FEA) of the mechanical behavior of the volume in response to stresses that would arise during reactor operation. By creating a mesh of the microstructure directly from experimental data and demonstrating FEA on this mesh, this work demonstrates a pathway for bridging the gap between experimental and modeling efforts in microstructure-based fuel performance models.