| The method of subliming solid materials and transporting them to the process system is often used in the process system,because these materials are easy to sublimate by heating.In the nuclear industry system,the feeding method of uranium hexafluoride sublimation is widely used in the UO2 fuel production process due to its simple operation and easy implementation.However,the control of uranium hexafluoride sublimation rate mainly relies on heat transfer test and worker’s operating experience,so there is a large margin to ensure safety.In this paper,the numerical simulation is used to calculate the sublimation rate of uranium hexafluoride using CFD technique,and the factors affecting the sublimation rate of UF6 are comprehensively explored through the joint simulation of one-dimensional system program and three-dimensional CFD program.First of all,there are three mass transfer equations that are common used in phase change simulation.They are Lee model,effective film theory and Langmuir equation,which are analyzed in this paper from three aspects:the applicability of calculation,the difficulty of obtaining calculation parameters,and the stability of calculation.According to the solid form of uranium hexafluoride,the numerical calculation model for CFD simulation of uranium hexafluoride sublimation process is devided into comparing the porous media model,the VOF model and the quasi-steady state model.Since the uranium hexafluoride solid obtained by freezing in the liquid state may be granular as a porous medium,simple two-dimensional calculations can be carried out through the porous media model.Considering that the sublimation process of uranium hexafluoride is very slow,uranium hexafluoride solid mainly exists in the form of agglomerated solids forming of gas de-sublimation.Also,comparing the simulation calculation results with the experimental results,the final simulation model is determined mainly from three aspects:the relative error of the calculation results,the calculation stability,and the calculation resources.Secondly,this paper analyzes the factors that may affect the sublimation rate from three aspects of thermodynamic analysis,kinetic analysis and heat and mass transfer analysis,and explores the effects of related factors through designed simulation experiments.Then a one-dimensional system simulation program is established for the control valve.Using this one-dimensional system and the three-dimensional CFD program to comprehensively explore the influence of the downstream pressure on the sublimation rate in the sublimation cylinder is described in this paper.Finally,this paper conducts simulation experiments in five aspects:the heating method of the wall heating temperature,the maximum wall heating temperature,the model the uranium hexafluoride container,loading volume of uranium hexafluoride,and the outlet pressure of the uranium hexafluoride container.Meanwhile,the sublimation rate,total sublimation time and energy consumption are considered to evaluate the numerical experimental results in this paper.The study finds out that using a non-linear heating method,increasing the maximum wall heating temperature 5-10K and higher outlet pressure can increase the sublimation rate,shorten the total time required for sublimation,and reduce the energy consumption in the production process.These are the suggestions given for the factory to optimize the uranium hexafluoride sublimation process and save production costs. |
