Numerical and experimental investigation of a new conceptual fluoride salt freeze valve for thorium-based molten salt reactor

Abstract

To improve the reliability and reduce energy consumption, a conceptual design of a freeze valve is proposed for the thorium-based molten salt reactor (TMSR) concept. Fins were utilized in this new design to enhance heat transfer and realize passive shut-off function, which could not be realized by the previous design. An experimental apparatus using the fluoride salt FLiNaK was constructed to conduct a series of preliminary solidification and melting experiments. In addition, the enthalpy-porosity method of ANSYS® Fluent solver was applied to simulate the solidification process of the salt at a specified operating temperature. Temperature distributions of the fluoride salt, solidification/melting time, and frozen plug effect were analyzed under natural convection heat transfer in an open space. The calculated salt temperatures exhibited good agreement with the experimental values. The results indicated that the range of effective operating temperature is 530–600 °C for the finned freeze valve. In this study, the ideal set operating temperature of the finned freeze valve was chosen as 560 °C to achieve competent performance. Moreover, 560 °C is additionally the highest set operating temperature for maintaining excellent cooling performance and sustaining deep-frozen condition of the salt plug. At this set operating temperature, the simulation data indicated that the molten salt in the flat part of the finned freeze valve will completely solidify at 10.5 min. The percentage of solid salt in the flat and lower transitional parts of the valve reaches 29.60% in 30.0 min. Furthermore, the surface temperature of the proposed freeze valve is 11.10% lower compared with that of the TMSR freeze valve at a cooling gas supply of 173 m3/h. Therefore, the new freeze valve was proven to be capable of reducing the energy consumption and realizing the passive shut-off function.