Molten salt reactor is a promising type of reactor with excellent safety and economy, benefiting from the stable properties of its molten salt coolant at high temperatures. However, the freezing point of molten inorganic salt is usually high enough to pose a risk of coolant freezing, which could plug the pipelines when flowing through a relatively cold place.

This study aims to present the process of the molten salt filling cold pipe with solidification-melting behaviors and estimate the mushy zone effect of molten salt with temperature near the freezing point.

The commercial CFD (Computational Fluid Dynamics) code ANSYS Fluent was used to numerically simulate the process, and the solidification-melting behaviors were solved by the enthalpy-porosity model, in which the mushy zone constant (Amush) was an important influencing parameter. By monitoring the velocity change of the characteristic interface, a set of penetration distances was simulated at different Amush values (5×10³~5×10⁵), and an existing experiment was used to deduce the mushy zone constant for molten salt.

Simulation results show that penetration distance is sensitive to variations in the mushy zone constant. Based on the existing experimental value of penetration distance,Amush=5×10⁴ is suitable to mushy zone influence estimation for molten salt.

Based on the method proposed in this study for determining the mushy zone constant, proper selection of mushy zone constant is very much necessary to accurately solidification-melting process prediction when using the enthalpy-porosity model whilst the freezing point of molten inorganic salt is usually high enough presenting a risk of coolant freezing which could plug pipelines when flowing through relative cold place.