Numerical Investigation Of Thermal-Hydraulic Characteristics Of Sodium Cooled Fast Reactor Once-through Steam Generator With Coupled Heat Transfer From Primary To Secondary Side

As the heat exchanger of secondary loop sodium and tertiary loop water in sodium cooled fast reactor(SFR),steam generator(SG)is a crucial equipment of nuclear island.Thermal hydraulic characteristics are the foundation of structural mechanics analysis,material analysis and hydrochemistry analysis,thus thermal hydraulic characteristics are one of the most crucial research contents of SG.In this study,integral and localized SFR SG thermal-hydraulic characteristics are investigated by numerical simulation and theoretical analysis.Micro-characteristics including turbulence and vortex of crucial construction parts are researched.Meanwhile,further understanding of flow and heat transfer characteristics of liquid metal are obtained.The study will establish foundation to SG safety analysis and structural optimization.Firstly,based on the structure characteristics of SFR SG and analyzation of SG thermal hydraulic characteristics,this study develops a thermal hydraulic calculation model with coupled heat transfer based on porous media model.SST k-? turbulence model is adopted to calculate the turbulent flow of primary side,and resistance models of tube bundles and the tube support plates(TSPs)are established.In order to calculate the flow boiling heat transfer characteristics precisely,secondary side is divided into four regions,i.e.,subcooled water,saturated boiling,film boiling and superheated steam.Secondary,grids of TSPs,primary side plenums and overall SG are generated by the bottom-up approach.The average value of elements quality is higher than 0.9.High-precision discretization schemes of governing equations are adopted to calculate the integral and localized three-dimensional thermal hydraulic characteristics of SG.The relative error of China Experimental Fast Reactor(CEFR)operating parameters between calculation result and design value is less than 0.1%.Thirdly,local hydraulic characteristics calculation of TSPs based on fine gird is analyzed.The results show that the cross flow energy of fluid peaks at the front of TSP and decreases rapidly because of the resistance of tubes.Vortex at the behind of TSP induces the rapid enhancement of turbulence intensity.The possibility of flow induce vibration of tubes is much higher in these two regions.Viscous resistance coefficients and inertia resistance coefficients of different TSPs are acquired by analyzing pressure drops of fluid flowing through TSPs when inlet velocities are at the range of 1~3m/s.The calculation results of primary side plenum hydraulic characteristics show that the throttling device can suppress the strong turbulent in annular chamber effectively,so that fluid in inlet plenum can flow through flow distribution device and enter tube bundles region steadily.Flow in outlet plenum is relatively steady.In both plenums,fluid is distributed evenly in radial direction.But the flow distribution in axial direction is non-uniform,and tubes of outer layers suffer scouring severely.Finally,overall SG thermal hydraulic characteristics are obtained by integral calculation based on porous media model.The high cross flow energy of primary side continue to influence downstream fluid.Pressure in tube bundles region decreases gradually along the flow direction.Velocity changes violently at the connections of annular chambers and connecting pipes,causing the high pressure drop there.Heat transfer characteristics of SG are influenced by temperature distribution and heat transfer coefficients on both side.Temperature difference in evaporator is relatively high,and boiling heat transfer will enhance the heat transfer ability of secondary fluid.Average heat transfer coefficient of evaporator and superheater is 3460.88W/(m2·K)and 1889.2 W/(m2·K)respectively.The heat transfer efficiency of evaporator is much higher than superheater.However,heat transfer coefficient and temperature difference will enhance significantly in nucleate boiling region when power decreases.And heat flux will rise rapidly in this condition,which may cause severely damage to SG.Based on the above work,the numerical investigation results in this paper can establish the foundation to mechanical analysis.Meanwhile,the results can provide references for further optimization of structural design.SG thermal parameters design and safety analyzation also need the calculation results as input value.The research has important significance for ensuring safe operation of SG.