Numerical Simulation Of Steam Condensation In Oscillation Region And Analysis Of Influencing Factors

Because of the strong condensation heat transfer ability of steam jet condensation process,it is widely used in advanced passive reactor safety system.For example,in a pressurized water reactor,when a large LOCA accident occurs in the containment of the reactor,a large amount of coolant vaporizes due to the pressure drop.As an effective method to prevent the overpressure failure of the containment,a large amount of steam is discharged into the spent fuel pool through the containment pressure relief pipeline to trigger the condensation and pressure relief process,and the steam jet condensation process is used to condense a large amount of steam,which is effective Reduce the pressure in containment.However,the pressure relief process is accompanied by strong pressure oscillation,which causes severe impact on the reactor fuel rod bundle assembly and the inner wall of the reactor containment.Steam condensation is a typical direct contact condensation phenomenon,which involves two-phase flow,gas-liquid phase transition and other complex processes,and the related research needs to be carried out in depth.In this paper,the steam condensation phenomenon in the oscillation region is simulated by numerical simulation.The main contents and conclusions are as follows:Based on the basic conservation equation,some key models,such as mass exchange model of bubble boundary layer,bubble control equation model,calculation model of steam pressure in bubble and pressure calculation model at any position in the pool are established,and the thermal hydraulic model for simulating the process of steam bubble cold condensation oscillation in water tank under high undercooling is constructed.The model of bubble radius and pressure in the pool was established to obtain the variation of bubble radius and pressure with time.Based on the high undercooling model,the non-spherical growth model of bubbles and the interference calculation model between bubbles are added.The steam energy equation in the bubble is used to calculate the average temperature of the vapor in the bubble.The expressions of the momentum conservation equation and the bubble control equation in the presence of the interference effect between bubbles and the non-spherical growth of bubbles are modified.A thermal hydraulic model was established to simulate the steam bubble condensation oscillation process in a pool with low subcooling.Based on the hypothesis of the model,the stability analysis method of steam condensing oscillation system based on the thermal hydraulic model in this paper is derived and presented,and the method is verified by specific experiments.Based on the low undercooling model and the high subcooling model,the influence factors of pressure oscillation amplitude and oscillation frequency are analyzed.The results show that the subcooled water temperature and outlet mass flow rate have significant influence on the amplitude of pressure oscillation of underwater steam jet,and the outlet mass flow rate is the main factor The oscillation frequency decreases with the decrease of supercooled water temperature or outlet mass flow rate.In this paper,the related thermal hydraulic model and influencing factors of steam condensation phenomenon in the oscillation region are studied,which provides technical reference for the study of steam condensation oscillation and system safety evaluation under nuclear reactor accident.