Molten salt reactor is a promising type of reactor in the fourth generation advanced nuclear reactor system due to its excellent safety and economy. However, as the coolant for the molten salt reactor system, lithium fluoride beryllium (FLiBe) has a melting point of 460 ℃, which is much higher than the ambient temperature, so there is a risk of coolant solidification in the system.

This study aims to establish a one-dimensional solidification model with mushy zone effect based on energy conservation and enthalpy porous medium model.

Firstly, based on the energy conservation equation, a solidification layer thickness model was established and a source term model with mushy zone was established based on the enthalpy porous medium model. The velocity and temperature distribution models were obtained on the basis of the boundary layer theory. Secondly, the molten salt solidification experiment was designed to verify these models. Finally, the system safety analysis program ASYST-SF was employed to simulate the filling behavior of FLiBe coolant in the pipe.

The experimental verification results show that the overall model error is less than ±10%, meeting the requirements of reactor system safety analysis. The evolution behavior of fluid temperature, solidification layer thickness, and pressure drop of the pipe filling behavior under typical working conditions are observed.

The model and calculation results are of great significance for improving the operational safety of molten salt reactors.