Development of an EDS-Based Grain Segmentation Method for MIMAS-MOX Nuclear Fuels

MOX (uranium-plutonium mixed oxide) nuclear fuels are generally manufactured using a MIMAS (micronized master blend)-type process resulting in ceramics presenting a microstructure composed of agglomerates of different plutonium contents. To allow for phase-dependent grain size analysis, we developed an SEM (scanning electron microscopy) method based on simultaneously collected EDS (energy dispersive X-ray spectroscopy) and EBSD (electron backscattered diffraction) maps. Posttreatment of the EDS/EBSD data allows constructing maps of plutonium-rich agglomerates, grain boundaries, and porosities, which are then combined in a single dataset. We then propose and discuss a criterion that can be applied for the attribution of each grain to the plutonium-rich or uranium-rich agglomerates. To validate this criterion, the EDS/EBSD results are compared to better chemically resolved mapping that can be obtained through EPMA (electron probe microanalyzer). Compared to the EPMA-/EBSD-based method previously reported in the literature, the EDS/EBSD method we present offers a simple and convenient way to gain insights about the interdependence between microstructural and chemical features, such as measuring grain size in the different phases present in MIMAS-type MOX fuels.