The effect of Ar ion beam irradiation on mesocarbon microbead-densified graphite as the matrix of fuel elements in molten-salt nuclear reactors

Mesocarbon microbeads (MCMBs) were added to the precursors of a traditional matrix A3-3 graphite to increase its density for use as the matrix of fuel elements to inhibit the impregnation of liquid fluoride salt in molten salt reactors. The physical properties of the densified graphite (MDG) obtained using MCMBs with different sizes were compared with those of the A3-3 graphite. Ar ion-beam irradiation by a 4 MV accelerator was used to obtain surface damage to ~1 μm depth in the specimens. Results show that the median pore sizes of the MDGs increase from 530 to 644 nm with the size of MCMBs increasing from 2 to 16 μm, but all are smaller than that of the A3-3 graphite (924 nm). The density is increased by adding MCMBs. The MDG prepared from MCMBs with a size of 2 μm has the highest resistance to irradiation hardening. Both the A3-3 graphite and the MDGs become amorphous at an Ar ion beam dose of 1.47 dpa.