Topography changes and microstructural evolution of nuclear graphite (IG-110) induced by Xe26+ irradiation

The microstructure of nuclear graphite, a key material in nuclear reactors, is affected by the high-flux irradiation. The damage to the graphite by irradiation is important for reactor safety. To understand the damage of nuclear graphite by irradiation, IG-110 nuclear graphite, a representative nuclear graphite, was chosen to investigate the change in morphology and microstructure caused by 7 MeV Xe26+ irradiation with peak damage doses of 0.1-5.0 displacements per atom (dpa) for samples of a size of 40.0 mm×40.0 mm×2.0 mm. The topography and microstructure of IG-110 were characterized by SEM, AFM, grazing incidence XRD, Raman spectroscopy and nano-indentation. Results indicate that after 7 MeV Xe26+ irradiation at a dose of 0. 11 dpa, a ridge-like structure appears on the surface of the IG-110 graphite, mainly in the binder region, and the surface roughness increases slightly. With a further increase of the irradiation dose, the ridge-like structure also appears in the filler region. At a dose of 0.55 dpa, pore shrinkage increases accompanied by pore closure, and the surface roughness also increases. The changes in topography and microstructure caused by irradiation are attributed to the expansion of graphite along the c-axis direction. With increasing irradiation dose the defect density and the degree of in-plane disorder in the graphene sheets increases, while the modulus and hardness of the graphite first increase and then decrease. Their increase is caused by dislocation pinning and closure of fine pores, while their decrease is attributed to an increase in porosity and the generation of an amorphous structure.