Research progress on gas-liquid separation experimental technology for thorium molten salt reactors

Liquid-fuel thorium molten salt reactors (LF-TMSRs), as a candidate technology for Generation IV advanced nuclear reactors, offer significant advantages such as enhanced safety, non-proliferation, and reduced nuclear waste. However, fission gases generated during operation, such as xenon and krypton, reduce reactor efficiency and stability. To mitigate the accumulation of neutron poisons, techniques such as helium injection, mass transfer, and bubble separation are employed. Consequently, gas-liquid separation has become a critical technology in the operation of LF-TMSRs, with the swirl vane gas-liquid separator serving as a key component in the gas removal system. This study summarizes experimental approaches for evaluating separation performance and investigating separation mechanisms in swirl vane gas-liquid separators, providing guidance for future research.

Gas-liquid separation experiments in TMSRs can be divided into separation characteristic experiments and flow field characteristic experiments. This paper reviews recent studies in both categories, summarizes the features of experimental systems and techniques, and provides suggestions for future research. Separation characteristic experiments focus on evaluating parameters such as separation efficiency and critical back pressure to assess separator performance and determine optimal operating conditions. The experimental setup typically includes subsystems for bubble/liquid supply, flow and pressure regulation, parameter measurement, and liquid circulation. Flow field characteristic experiments utilize visualization systems to analyze two-phase dynamics, including air core morphology, bubble trajectory and morphology, and liquid phase velocity fields, using advanced technologies such as high-speed imaging and particle image velocimetry.

The different forms of the gas phase, such as the air core and bubbles, serve as visual indicators of separation performance. Ideally, a stable, rod-like gas core forms within the separator, and the bubbles concentrate along the central axis before discharge. However, factors such as back pressure, Reynolds number, and swirl number can cause deviations in air core morphology. Additionally, the bubble axial separation length, measured from initial injection to final coalescence into the air core, reflects the difficulty of separation. Shorter separation lengths usually correspond to higher separation efficiency, indicating satisfactory design or operating conditions. To further understand the microscopic separation mechanism, studies have examined swirl flow velocity distribution and bubble morphological evolution. Quasi-Rankine vortices dominate the flow structure, with swirl intensity initially increasing and then decreasing. As bubbles approach the central axis of the separator, their shapes flatten and eventually form asymmetric cap or cashew-like morphologies due to centrifugal and pressure gradient forces induced by the swirl flow.

Given the complexity of the flow dynamics within the separator, extensive experimental studies have evaluated separator performance and investigated underlying mechanisms. Future research should focus on extending experiments to hot-state conditions, collaboratively optimizing guide vane parameters, and developing a unified theoretical model to describe the complex bubble interactions, thereby advancing the understanding of gas-liquid separation mechanisms in LF-TMSRs.