Equipment design and experiment of compatibility test of nuclear graphite and molten salt

[Background] Thorium molten salt reactor (TMSR) is a nuclear fission reactor using nuclear graphite as neutron reflector and moderator and molten 2LiF-BeF₂ (FLiBe) salt as primary coolant. In TMSR, graphite is directly in contact with the molten salt. Given the porous nature of graphite, molten salt may penetrate into its pores in molten salt reactor environments, which may change graphite's thermal and mechanical properties. [Purpose] This study aims to verify whether the FLiBe salt penetrates into candidate nuclear graphite and to test the amount of infiltrated molten salt, which is of vital importance to the safety in operation of the reactor. [Methods] An equipment used for static infiltration tests was developed to investigate the infiltration rate of molten FLiBe salt into graphite materials under different pressures. Effects of temperature and duration on the molten salt infiltration behaviors of graphite materials were also studied. [Results] The threshold pressure for FLiBe salt infiltration for TMSR candidate graphite T220 was between 600 kPa and 700 kPa at 700℃. The higher the infiltration pressure, the greater the infiltration rate, while the increase amplitude decreased gradually. The infiltration rate of three grades of graphite after infiltration tests in different temperatures (600℃. and 700℃.) and durations (20 ∼ 2000 h) showed no significant difference. [Conclusion] FLiBe salt could not penetrate into graphite T220 in TMSR environments ( < 500 kPa). Both factors of temperature and duration had little effects on infiltration behaviors of graphite materials.(authors)