Characterization of oxygen transport in a lead-bismuth natural circulation loop

To investigate the oxygen mass transfer characteristics of a lead-bismuth natural circulation loop, numerical simulations of flow, heat transfer, and oxygen mass transfer processes were conducted using COMSOL software. The study found that during the start-up phase of natural circulation, the temperature and flow fields in the expansion tank underwent significant changes. While the oxygen concentration in bismuth could be adjusted dynamically and effectively by setting an appropriate H 2 /H 2 O partial pressure ratio, the mass transfer during this phase accounted for only a small proportion of the overall process. Using a computational model with coupled multiphysics fields, the flow velocity, temperature distribution, and oxygen mass transfer in the liquid bismuth recirculation circuit were calculated. Results indicated that oxygen control, achieved by adjusting the H 2 /H 2 O partial pressure ratio, facilitated both oxygen enrichment and reduction processes. Additionally, the average mass transfer coefficient of interfacial oxygen concentration was positively correlated with heater power and the secondary-side temperature of the heat exchanger. The coefficient changed abruptly when the initial oxygen concentration approached the interfacial oxygen concentration, primarily due to the dominant role of diffusion at that stage. It was further observed that the average mass transfer coefficient remained constant when there were large differences in oxygen concentration, providing valuable insights for predicting the mass transfer efficiency of the entire loop. This study quantitatively analyzed the flow, heat transfer, and oxygen mass transfer characteristics of a lead-bismuth natural circulation loop, offering critical data for experiments and system design. • Developed a multi-physics field model for gas-phase oxygen control of a liquid lead-bismuth natural circulation recirculation loop • A loop oxygen concentration prediction model was developed for the stable mass transfer coefficient stage