Study On The Phennomenon Of Turbulent Penetration In Pressurizer Surge Line And Analysis Of Thermal Fluid Solid Coupling

In the operation process of PWR nuclear power plant,the pressure of the main pipeline is large.In order to ensure the smooth operation of the whole nuclear power pipeline system,it is necessary to install a pressurizer on the main loop to maintain the pressure constant.The surge line of the pressurizer is a section of pipeline connecting the main loop and the pressurizer,which is generally T-junction.The fluid in the main pipe and the pressurizer flows in and out through the surge line.Because of the particularity of its structure and function,there is a mixture of high-speed and low-speed,high-temperature and low-temperature fluid in the surge line.Therefore,the flow and heat transfer state of the fluid in the tube is very complex,resulting in turbulent penetration phenomenon,leading to the fluctuation of the pipeline temperature causes the thermal deformation and thermal fatigue,which threatens the safety of the whole nuclear power system.The main research of this paper is as follows:(1)The flow and heat transfer of the flow field in the pressurizer surge line are simulated by the large eddy simulation method,and the theoretical analysis of the simulation results is carried out to explore the influence of momentum ratio,temperature difference,pipe diameter ratio and other factors on the turbulent penetration phenomenon in the tube.(2)According to the results of flow field simulation,using the CFD-FEM coupling method,the finite element analysis of the solid domain of the pipeline is carried out,and the temporal and spatial distribution law of the thermal deformation,thermal stress and other parameters of the pipeline under the turbulent penetration condition is obtained.(3)Using the fatigue theory,the stress fluctuation information is analyzed,and the fatigue life of the pressurizer surge line under different constraint conditions is obtained.The coupling calculation results show that:the momentum ratio and diameter ratio of the main and branch pipes have a significant impact on the turbulent penetration phenomenon,while the temperature difference between the main and branch pipes has a relatively small impact;the turbulent penetration phenomenon will cause thermal fatigue of the pipeline,the structure of the surge line will affect the fatigue life of the pipeline,and the fatigue life of the parallel structure is higher than the vertical structure.In this paper,based on the previous studies,the flow and heat transfer state of the fluid,the thermal stress and the thermal fatigue of the pressurizer surge line are theoretically analyzed and explored by the CFD-FEM coupling method.A series of conclusions are drawn,which provide a certain basis for the fatigue safety of the pressurizer surge line.It has a certain reference value for the optimization of the pipe structure of the surge tube.