The optical texture of PGA, Gilsocarbon, NBG-18, and IG-110 nuclear graphite

Abstract

Graphite will be used as a structural and moderator material in high-temperature gas-cooled reactors. While the microstructure of nuclear graphite, such as filler particles and porosity, has been intensively studied, little attention has been paid to the optical texture. The optical texture, which means the appearance of carbon under polarized light, describes the arrangement of graphite crystallites in terms of the shape, size, and orientation of the domains. It controls the properties of coke and is a classic concept in the field of carbon materials. This study reports the optical texture characterization of nuclear graphite: PGA, Gilsocarbon GCMB, NBG-18, and IG-110. Under polarized light, some previously unnoticed structural features, such as flour particles in PGA and Gilsocarbon GCMB, binder barrier with fused coarse mosaic in Gilsocarbon GCMB, granular domains, and isotropic carbon matrix in NBG-18 are reported and discussed. Point-counting method was applied to polarized light images to quantitatively determine the volume faction of each structural component in nuclear graphite. Updated structural models based on quantitative optical texture analysis will provide a better understanding of the structure-property relationship of nuclear graphite.