Study On Extraction Characteristics Of Tritium Column From Liquid Lead Lithium Based On Bubble

The liquid lead lithium(PbLi) tritium breeding blanket has many significant advantages such as simple structure,high tritium breeder ratio,high thermoelectric conversion efficiency,and online tritium extraction and material exchange,which makes it one of the most promising liquid blanket designs for fusion reactors.The safe and efficient extraction of tritium from liquid PbLi alloys is an important guarantee for the feasibility of the design solution for the liquid PbLi tritium breeding blanket.The bubble column is a continuous gas-liquid contact reaction equipment,which is chosen to extract tritium from liquid PbLi alloy due to its simple structure and high heat and mass transfer efficiency.The gas-liquid two-phase flow and mass transfer characteristics in the bubble column are the main focus of the research to design and optimize the bubble column.Due to the high cost of tritium and the strong permeability and radioactivity of tritium,it is difficult to experimentally study the gas-liquid two-phase flow and mass transfer characteristics in the bubble column.Therefore,the purpose of this paper is to conduct a simulation study on the gas-liquid two-phase flow and mass transfer characteristics in a bubble column to provide a new method for the design and optimization of bubble column.Numerical simulation of gas-liquid two-phase flow and mass transfer characteristics in a bubble column is carried out in three steps:First,in this paper,a single bubble in a bubble column is selected as the object of study,and the simulation of single bubble motion and tritium transport process between gas-liquid phases is carried out based on the level set coupled dilute matter transfer model using COMSOL Multiphysics 5.6 software.The simulation results show that the initial stationary helium bubble starts to rise in liquid PbLi under the buoyancy effect.The tritium concentration inside the bubble starts to increase while the tritium concentration in the liquid PbLi around the bubble decreases,and finally the bubble reaches the gas-liquid interface and merges with the helium above the vessel and exits through the top outlet of the vessel to extract tritium from the liquid PbLi.The simulation results better verify the feasibility of using the level-set coupled dilute matter transfer model to study the gas-liquid two-phase flow and tritium transport process.Secondly,the He inlet is introduced on the basis of the single bubble motion model,and the tritium in liquid PbLi is continuously extracted by blowing helium into the liquid PbLi to generate bubble populations.The effects of different He flow rates on the local flow field and gas content of the bubble column and the effects of different thermodynamic parameters(inlet helium flow rate,initial tritium concentration in PbLi and liquid PbLi filling height)on the local tritium extraction efficiency of the bubble column were analyzed based on the simulation results.The results of the analysis show that increasing the inlet helium velocity increases the liquid phase circulation rate and the gas holdup in the bubble column.Appropriately increasing the helium inlet velocity of the bubble column is beneficial to improve the tritium extraction efficiency of the bubble column.The tritium concentration in the initial liquid PbLi has a slight effect on the tritium extraction efficiency of the bubble column.Increasing the liquid PbLi filling height leads to a decrease in the tritium extraction efficiency of the bubble column.Finally,based on the simulation study of tritium extraction process in the local model of the bubble tower,the simulation study of tritium extraction process in the global model of the bubble tower was carried out,and the design scheme of the multi-stage tandem tritium extraction system in the bubble tower was given.The results show that the fluid inside the bubble tower is unevenly distributed along the radial direction,and there is a serious wall flow effect,and the tritium extraction efficiency is only 20.8%.In the tandem operation mode,the total tritium extraction efficiency of the bubble tower will reach 95% when the number of bubble tower tandem stages is 13.