Abstract
The Mark 1 pebble bed fluoride-salt-cooled high-temperature reactor (Mk1 PB-FHR) is a promising kind of molten salt reactor (MSR) design that is cooled with molten salt, fueled with TRISO-based fuel, and equipped with the advanced direct reactor auxiliary cooling system (DRACS) for decay heat removal. The use of molten salt endows the reactor can be operated at low pressure while at very high temperatures. Additionally, the excellent natural circulation capability of the molten salt makes the FHR features passive safety, which can remove the decay heat without an external power supply. However, the freezing point of molten salt is much higher than the ambient, which arises a new risk of coolant solidification accidents. The hot molten salt was cooled by the cold water in the DRACS which is highly susceptible to the coolant solidification accidents. The failure time of the DRACS after the reactor shut down is critical for the safety of the reactor system. In this study, a transient solidification model was employed and coupled with the ASYST code to investigate the complete failure time of the DRACS. Besides the conventional design of DRACS, two different optimal designs were applied to investigate the solidification behavior of the molten salt. On the premise of satisfying the limited temperature of the reactor system, the optimal design was obtained according to the principle of as long as possible the failure time.
