Effects of Nanocrack Behavior on Radiation-Induced, Elastic Modulus Changes in Nuclear Graphites

The elastic responses of nuclear graphites depend not only on the graphitic content itself but are largely dictated by the microstructural constitution of the material. The types of raw materials combined with the manufacturing processes used to produce the graphite yield the microstructural content which primarily includes graphite filler, graphitized pitch binder, and voids/defects that typically occupy approximately 20% of the volume. Among these microstructural components, porosity, microcracking (considered to be part of voids/defects) and intracrystallite nanocracking (Mrozowski cracks) heavily influence the overall properties of the material including the elastic moduli. Models describing the elastic moduli of porous, polycrystalline graphite materials have been developed to interpret experimental determinations of Young's modulus and shear modulus in oxidized graphites, and these include the effects of nano/microcracks. This work will demonstrate the role that the effects of neutron irradiation on Mrozowski cracks could have on the phenomenon of turnaround in nuclear graphites and will present directions to be pursued to account for microstructure-related effects that generally occur as a result of neutron irradiation.