Texture analysis of AGR program matrix materials

•Ellipsometry can be used to measure texture of graphite matrix material in HTGR integral fuel forms.•Processing influences texture with alignment of graphite flake to normal to pressing direction.•Overcoating results in local texture and alignment of graphite flake normal to particle outer surface. The fuel form for high-temperature gas-cooled reactors consists of tristructural isotropic (TRISO) particles embedded in a matrix of graphite flake and carbonized resin. The process of overcoating particles prior to compacting yields a circumferential orientation of the graphite flake surrounding the TRISO particles, which is modified to varied extents when overcoated particles are pressed into the final fuel form. As graphite is highly anisotropic, the texture may impact the properties and performance of the fuel. Ellipsometry was used to measure the texture of the matrix for fueled compacts and unfueled “matrix-only” samples. Results indicated local texture related to the spherical particles in compacts associated with overcoating versus a more linear layered structure in “matrix-only” samples.