The gas-lift pump has been adopted to enhance the natural circulation capability in the type of lead-bismuth alloy cooled reactors such as ADS and LMFR. The natural circulation ability and the system safety are obviously influenced by the two phase flow characteristics of liquid metal-inert gas. In this study, the numerical research has been performed to evaluate the natural circulation capability of lead-bismuth cooled ADS with gas-lift pump. The drift flow theory, void fraction prediction model and friction pressure drop prediction model have been adopted in this numerical simulation. The effects of the gas flow rate, the bubble diameter and the height of ascension pipe on natural circulation capability of gas-lift pump have been analyzed. The results showed that in bubbly flow pattern, for a fixed value of gas volume flow rate, the natural circulation capability increased with the decrease of the bubble diameter. In the bubbly flow, slug flow, churn flow and annular flow pattern, with the gas volume flow rate increasing, the natural circulation capability initially increased and then declined. As the height of ascension pipe increased, the natural circulation flow rate went up. Besides, the flow parameters influenced the thermal hydraulic characteristics of the reactor core obviously. Therefore, in the practical engineering application, the suitable gas volume flow rate, bubble diameter and the height of ascension pipe are important parameters to the capability of natural circulation in lead bismuth alloy loop of this research. The present work is helpful for revealing the law of enhancing the natural circulation capability by gas-lift pump, and providing theoretical basis of the optimization design of cooling and system safety.

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