Effects of bayonet tube leak on the heat transfer characteristics of fuel drain system in molten salt reactor

<bold>Background</bold>The liquid-fueled molten salt reactor (MSR) is one of the candidates for the Generation IV reactor technologies, and the fuel drain system is a special safety design.<bold>Purpose</bold>This study aims to investigate the influence of inner barrier leak of one heat exchange element of MSR on heat transfer characteristics.<bold>Methods</bold>Firstly, the fuel drain system of Molten Salt Reactor Experiment (MSRE) was taken as the research object, and computational fluid dynamics (CFD) simulation methods were employed to construct heat transfer and multiphase flow models to analyze the heat transfer and flow phenomena under normal operation and bayonet tube leak scenario. Then, the sensitivity analyses of key influencing parameters, such as the leak size (3~8 mm), leak location (10~1 500 mm above the lower end of the heat exchange element) and pressure in the annular gas space (ranging from -13 788 Pa to 13 788 Pa), were carried out.<bold>Results</bold>The analysis results show that 18.4% of cooling water flows out from the leak location through the annular gas space when bayonet tube leak occurs and the power of one single heat exchange element increases to 29.434 kW. In addition, the lowest abnormal temperature appears in the thimble near the leak location. The sensitivity analysis results present that the heat transfer varies with the leak size, leak location and pressure of annular gas space and is most sensitive to leak size.<bold>Conclusions</bold>These analysis results of this study are valuable to the engineering design of the fuel drain system for MSRs.