Transient analysis of tritium transport characteristics of thorium molten salt reactor with solid fuel

Tritium management is a vital factor that needs to be considered before a molten salt reactor (MSR) or fluoride-salt-cooled high-temperature reactor (FHR) is constructed. The analysis of tritium transport characteristics under steady and transient conditions is essential in the conceptual design of MSRs and FHRs. In this study, tritium transport characteristics analysis is conducted for a fluoride-salt-cooled pebble bed reactor, i.e., thorium molten salt reactor with solid fuel (TMSR-SF) under accident conditions. The tritium transport characteristics analysis (TAPAS) code is improved with a power model and heat-and-mass transfer model to adapt to TMSR-SF. The transient responses of the tritium transport characteristics of TMSR-SF under the unprotected reactivity insertion accident (URIA) and unprotected overcooling accident (UOC) are determined. It is found that the amount of tritium fluoride (TF) adsorbed on graphite varies, indicating the dynamic equilibrium between the TF adsorption and desorption on graphite. Due to the nuclear density variations of Li-6 and Be-9 in the fluoride salt under the accident conditions, the tritium production rate increases and decreases under the UOC and URIA conditions, respectively. Generally, under these two accident conditions, the tritium permeation rates are lower than that of the normal operation condition. In these cases, it is unnecessary to develop extra safety facilities for tritium control. This study contributes to the tritium management of TMSR-SF.