Irradiation resistance study of binderless nanopore-isotropic graphite for use in molten salt nuclear reactors

Binderless nanopore-isotropic graphite (NPIG) produced from mesocarbon microbeads by isostatic pressing method was irradiated with 7 MeV Xe26+ to a total peak dose of 0.1, 0.5, 2.5 and 5.0 dpa. The effect of the irradiation on the microstructure and physical properties of NPIG was then evaluated and compared against the performance of isostatic nuclear graphite (IG-110, TOYO TANSO CO., LTD). Ion-irradiation has a different effect on the microstructure (crystallinity, crystallite size) and mechanical properties (hardness, Young's modulus) of NPIG and IG-110 graphite. At lower irradiation doses, the surface morphology of NPIG was fragmented in a similar way to that of IG-110, but the NPIG gradually balled at 5 dpa. X-ray diffraction results show that NPIG has a lower degree of graphitization than IG-110. Raman studies indicated that NPIG reached saturation at lower doses. The nanoindentation showed that the hardness and Young's modulus of the NPIG and IG-110 increased after irradiation. Transmission electron microscopy images also provide clear evidence for an irradiation-induced increase in the number of basal dislocations and defects. Thus, although NPIG is generally more sensitive to irradiation than IG-110, its hardness is actually less affected.