Sparging-based fission gas separation technology for molten salt reactor

Abstract

Thorium molten salt reactor is one of the GEN-IV Molten Salt Reactors currently developed in China. The online removal of fission gases like Xenon and Krypton is a crucial technique to achieve high burnup of the liquid nuclear fuel. One of the promising candidates for practical application is the bubble sparging method, where tiny bubbles are first introduced into the liquid fuel, then the fission gases migrate to the carrier bubbles by interfacial mass transfer, and finally, a gas–liquid separator is used to remove the carrier bubbles along with the absorbed fission gases from the liquid. A thorough understanding of the mechanism and accurate modeling for the three sub-processes mentioned-above, namely bubble generation, mass transfer, and gas–liquid separation, are necessary for quantitative control of the fission gas removal performance.As for the bubble injection, the microbubble generating approach based on turbulent fragmentation mechanism is proposed, the predicting model of bubble diameter and the design criterion of bubble generator were established, constructing a generation and control technology of microbubbles for molten salt medium. For the mass transfer process, a novel numerical method simulating the interfacial migration of dissolved gases in bubbly flow is developed. Besides, a compact gas–liquid reactor with enhanced mass transfer efficiency applied to nuclear installations is proposed. In terms of the separation of bubbles, the separation length and stability of the swirling flow gas–liquid separator are investigated, and a solution of gas–liquid separation with ultra-high separation efficiency under extremely low gas fraction conditions is proposed. The feasibility and efficiency of the fission gas separation technology integrating all three procedures have been evaluated experimentally, providing a solid foundation for the future online post-processing of both off-gas and liquid fuel.