Numerical Study Of Impurity Distribution In Two-phase Flow On The Secondary Side Of Steam Generator

During the operation of nuclear power systems,leakage accidents of primary and secondary condensers are prone to occur,causing seawater to enter the secondary circuit,and impurities such as chloride ions enter the steam generator together with the water supply in the secondary circuit,and enrich near the heat transfer tube.It is easy to cause wear and corrosion of the heat exchange tube of the steam generator,threatening the safe operation of nuclear power plants.At present,the numerical simulation methods of impurity migration and diffusion and impurity particle deposition under the first and second side-coupled heat transfer conditions are not mature enough.Numerical studies on flow heat transfer,impurity migration and particle deposition under multi-tube coupled heat transfer conditions of steam generators are carried out to provide a scientific basis for the design,optimization and operation of steam generators.In order to study the migration and diffusion process of impurity chloride ions on the secondary side of the steam generator,a three-dimensional multi-tube physical model of fluidsolid coupling heat transfer on the primary side of the steam generator and the secondary side of the U-shaped heat transfer tube was established.By numerical simulation of fluid flow and heat transfer between U-shaped bundles,the DPM model reveals the distribution law of key parameters such as vapor fraction,temperature,velocity,and pressure between U-shaped bundles.By simulating the diffusion and migration of chloride ions in two-phase flow,the influence of thermal-hydraulic parameters on the secondary two-phase flow of impurity migration and the effective diffusion coefficient of chloride ions on the concentration distribution of chloride ions was studied.By simulating the movement and deposition process of impurity chloride ion particles,the Reynolds mainstream number was studied.Effect of bending radius on particle deposition on wall surface of U-shaped heat transfer tube.The calculation results show that the numerical model adopted in this paper can accurately simulate the flow field distribution under the coupled heat transfer condition of the primary and secondary side of the steam generator in the actual operation process,and the flow boiling characteristics and pressure variation law of the primary and secondary side of the steam generator under the design condition are obtained.Through the impurity migration model chosen,the migration law of chloride ions on the secondary side and the distribution of chloride ions on the secondary side in the coupled heat transfer process of the primary and secondary sides of the steam generator are obtained.The synergistic effect of the boiling intensity and turbulence intensity of the coolant affects the migration and diffusion of chloride ions.Chloride particle deposition occurs mainly in the bend area of the heat transfer pipe.The influence of mainstream Reynolds number on particle deposition is mainly reflected in the difference in deposition amount.Particle diameter affects particle deposition.With the increase of particle diameter,particle deposition thickness peaks at different bending pipe positions under the influence of particle stress.Overall,the deposition amount of the lower wall surface is greater than that of the upper wall surface,and the deposition amount of the side wall surface is also at a low level.In addition,the deposition thickness of particles increases as the bending radius of the U-shaped heat exchange tube decreases.Unlike the influence of the mainstream Reynolds number,the particle St number will change the deposition morphology of particle facies,and then change the deposition position and thickness of particles on the wall.This research method is of great significance for the prediction of impurity deposition area under two-phase boiling flow of steam generator,and also provides a reference for the structural optimization design of a U-shaped heat transfer tube under chloride ion corrosion environment.