Numerical Simulation On Temperature Fluctuation Of Liquid Sodium Near Outlet Of The Core In SFR Based On A 7-assembly Model

The sodium fast reactor(SFR)core is composed of fuel assemblies with different fuel enrichment levels,which in turn are composed of different rod bundles,such as fuel rods,control rods,and so on.In the core outlet of sodium fast reactor,mixture of hot and cold flow from different fuel assemblies can induce temperature fluctuation of liquid sodium near the central measure column.The temperature fluctuation of liquid sodium may cause high-frequency thermal fatigue of the central measure column,which may result in damage to the central measure column.In order to evaluate the thermal fatigue caused by fluid temperature fluctuation,the amplitude and frequency of temperature fluctuation are needed.This kind of temperature fluctuation must be studied for design and safety analysis of the central measure column.In the previous researches,limited by experimental conditions and computer capability,only very simplified models are used for experimental or simulation calculation.In the early stage,the researchers applied the parallel two-jet model and the parallel triple-jet model to carry out experiments and calculations,and obtained the two-dimensional temperature fluctuation results.Later,the coaxial jet model was used to study the temperature fluctuation in three dimensions.Recently,researchers have applied a 3-assembly model to simulate calculations.But all of them cannot fully reflect the real characteristic of the temperature fluctuation of liquid sodium near the central measure column.In order to obtain more credible simulation on the nature,it is necessary to increase the number of assembly for modeling.In this paper,a 7-assembly model is proposed to simulate the temperature fluctuation and flow behaviors of liquid sodium at the core-outlet district near the central measure column.Compared with the computational results from the 3-assembly model,many new characteristics appeared from the 7-assembly model.Since the 7-assembly model is more realistic,the calculation results from the7-assembly mode are more reliable.In addition,the influence of inlet flow on temperature oscillation is analyzed by comparing the calculation results of various working conditions.The velocity and temperature distributions of the flow field are analyzed along the radial direction,axial direction and different azimuth angles respectively.The time domain and frequency domain graphs are compared to analyze the variation rules of the temperature oscillation frequency and amplitude.It is found that the temperature oscillation is more intense when the flow rate at the inlet of the center-side operating head is consistent and the flow rate is higher.