Preparation of binderless nanopore-isotropic graphite for inhibiting the liquid fluoride salt and Xe135 penetration for molten salt nuclear reactor

Mesocarbon microbeads and the isostatic pressing method were used to prepare binderless nanopore-isotropic graphite (NPIG) as a neutron moderator and reflector, to inhibit liquid fluoride salt and Xe135 penetration during use in a molten salt nuclear reactor. The microstructure, thermophysical, and other properties of the NPIG were studied and compared with isostatic graphite (IG-110, TOYO TANSO CO., Ltd., Japan). A high-pressure reactor and a vacuum device were constructed to evaluate the molten salt and Xe135 penetration in the graphite, respectively. The results indicated that NPIG possessed a graphitization degree of 74% and excellent properties such as a high bending strength of 94.1 ± 2.5 MPa, a high compressive strength of 230 ± 3 MPa, a low porosity of 8.7%, and an average pore diameter of 69 nm. The fluoride salt occupation of IG-110 was 13.5 wt% under 1.5 atm, whereas the salt gain in NPIG remained steady even up to 10 atm with an increase of <0.06 wt%, demonstrating that the graphite could inhibit the liquid fluoride salt infiltration effectively. The helium diffusion coefficient for NPIG was 8.76 × 10−5 cm2/s, much less than 1.21 × 10−2 cm2/s for IG-110. The NPIG could effectively inhibit liquid fluoride salt and Xe135 penetration.