Numerical Simulation On Thermal Striping Of Pressurizer Surge Line At PWR Nuclear Power Plants

Surge line thermal striping indicates a phenomenon of hot and cold fluid interface fluctuation in pressurizer surge line.Reactor heat up processes is the important period of thermal striping phenomenon.Because of hUnigraphics NXe difference between fluid in primary pipe and pressurizer,slight oscillation in the fluid field will results in temperature field change observably.It will result in the changes of cyclical thermal stress of pipe contacted with the interface,which will lead to the fatigue of surge line,the generation of crack and penetration of the pipe wall,and will threaten the integrity of the primary loop at PWR.In this thesis,numerical studies were applied for the investigation of thermal striping,the following conclusions can be made:(1)Numerical simulation results on thermal stratification of the M310 pressurizer surge line were compared with the experiment.Dynamic Smagorinsky eddy viscosity model is more reasonable to the simulation of the temperature filed and the flow filed distribution in surge line than two equation turbulent models based on ? equation;(2)From the numerical simulation results,the thermal striping phenomenon can be observed obviously during reactor heat up processes.The study shows that the main reason of thermal striping in surge line is Kelvin-Helmholtz instability;(3)The method which could evaluate intensity of thermal striping in surge line was proposed in this study.Firstly,conducted fast Fourier transformation on transition temperature distribution in surge line which obtained by computation fluid dynamic code.Then,using simulation results in frequency domain and frequency response function which has been proposed could evaluate intensity of thermal striping in surge line.;(4)Intensity of thermal striping in surge line will increase with the increasing of temperature difference of coolant in pressurizer and hot leg.The intensity will also increase with the increasing of inlet velocity of hot leg.Intensity of thermal striping in surge line will first increase and then decrease when outlet velocity of pressurizer change from 0.013m/s to0.07m/s;(5)When the horizontal angle between surge line and hot leg changes from 0° to 0.5°,the intensities of the monitoring sections in surge line closed to hot leg will increase.Changing the diameter of surge line under the condition of constant outlet flow of pressurizer,and the outlet velocity at 0.013m/s or 0.052m/s,the intensity will decrease.By using CFD method,the mechanism of thermal striping in surge line and the factor which will influence the thermal striping in surge line are revealed.The method for evaluating the intensity of thermal striping proposed by this study can provide a theoretical basis of the evaluation of thermal striping which will contribute to the scheme improvement of surge line geometry design.