Microstructural analysis of nuclear grade graphite materials

Graphite materials under nuclear services undergo very significant irradiation effects including dimensional instability and modifications in various thermo-physical and mechanical properties^(1-4). Because these changes are resulting from the irradiation-induced structural changes the graphite in nano-, micro- and meso-scopic scales, it is essential to adequately characterize the materials' structures before and after neutron irradiation and to correlate the structural changes with the evolving macroscopic properties. Objective of this work is to characterize the microstructures of the as-fabricate fine-grained nuclear graphite manufactured by Tokai Carbon Co., Ltd. The graphite consists of filler cokes, binder, pores, and inherent cracks. The characteristic microstructures of the fine-grained isotropic graphite were determined by focusing on the attributes of these elements. Specifically, the sizes, shape factors, and the crystallographic anisotropy were evaluated so that these properties may be correlated with the thermophysical properties, macroscopic anisotropy, fracture properties, and the irradiation effects on them. In future work, these materials will be examined for various properties and microstructural changes by the neutron irradiation in the High Flux Isotope Reactor, Oak Ridge National Laboratory. This paper gives the initial results of microstructural evaluation for the pre-irradiated materials.