| Abstract Scope |
Commercial grade graphite used for core components in nearly all High Temperature Reactor (HTR) graphite-core designs is composed from a complex composite mixture of carbonized and anisotropic graphene-like phases, with a healthy amount of porosity thrown into the microstructure. Yet the (bulk) material properties display a near isotropic response even though graphite is composed from graphene-like structures which respond anisotropically. On one hand, the atomic length-scale irradiation response is nearly completely anisotropic with atomic displacement imposing shrinkage in the a-axis crystallographic direction and expansion within the c-axis direction. On the other hand, the irradiation macroscopic (bulk) response is near-isotropic. This discussion will review this unique irradiation material behavior, discuss crystallographic versus macroscale response, and speculate on how the microstructure may be influencing the overall isotropic behavior. New information and the latest thoughts on how this complex mixture of disparate phases can account for the odd behavior will be discussed. |