The liquid-fueled molten salt reactor (MSR) is one of the focuses of nuclear energy research, and the emergency fuel salt drain system is its unique and important safety system.

This study aims to analyze the effects of heat exchange element thimble leakage on thermal transfer characteristics of the water-cooled fuel salt drain system of MSR.

First, the molten salt reactor experiment (MSRE) water-cooled emergency fuel salt drain system was taken as the research object, and the computational fluid dynamics (CFD) simulation was conducted to establish a multiphase heat transfer flow model including cooling water boiling and molten salt solidification. Then, based on this model, the heat transfer and flow phenomena of the heat exchange element after the thimble leakage were analyzed. Subsequently, sensitivity analyses of leak size in the range of 2~7 mm, leak locations above the bottom of thimble in the range of 0.01~1.25 m, and the pressure difference between the annular gas space and the fuel drain tank (ranging from 20 684 Pa to 48 258 Pa) were investigated.

The analysis results indicate that the molten salt flows into the annular gas space in a short time after the leakage of thimble, resulting the heat exchange power of the heat exchange element increases and the natural circulation rate accelerates. When the leak size is below a critical threshold of 5 mm, the molten salt is frozed in the annular gas space, preventing further leak of the molten salt. Otherwise, the molten salt flows out of the annular gas space and the mass flow rate of cooling water in the bayonet tube oscillates periodically. In addition, the leak location and pressure difference also affect the mass flow rate of the cooling water and heat exchange capacity of the bayonet tube.

Results of this study provide valuable data for the engineering design of the fuel drain system for liquid-fueled MSRs.