Numerical Study Of Subcooled Boiling In Pwr Rod Bundle Channels

In this research,spacer grid is installed in the fuel assembly and the core of Pressurized Water Reactor(PWR).This fixes and supports the fuel rod bundle and affects the thermal and hydraulic performance of the fuel assembly.This spacer grid is generally divided into three types: the simple spacer(SS),the non-mixing vanes(NMV)and the spacer with mixing vanes(MV).It was observed that the installation of spacer grid in the springs,dimples and mixing vanes changes the original coolant flow direction.This makes the coolant flowing between fuel bundles flow in a transverse manner,increasing the thermal efficiency between the coolant and the fuel bundle.This results in an enhanced thermal hydraulic performance of the whole fuel assemblies.However,there are small components in the spacer grid that obstruct coolant flow.Hence,increasing the pressure drop of the coolant.Traditionally,most of the numerical simulation and experimental studies done on the core bundle channel of PWR tend to simulate the heat transfer of single-phase flow under high temperature and high pressure.However,there are only few studies performed on sub-cooled flow boiling in the core.In the quest to improve the power output and safety performance of PWR,some new improvements and designs have been made to allow a little sub-cooled boiling two-phase flow heat transfer to occur in the core of PWR.Therefore,this research seeks to perform CFD numerical study of fuel rod bundles under the condition of sub-cooled flow boiling.This research can provide references for related researches in the future and save research costs.First of all,based on Euler-Euler two-fluid six-equation model,this paper compares the single-channel sub-cooled boiling two-phase flow heat transfer test data and numerical calculation data in the round tube and PSBT international benchmark test,and verifies the reliability of numerical calculation.Secondly,using Solid Works modeling software,a reasonably simplified geometric model was built using CFD analysis and ICEM CFD software to make model grid mesh.Reasonable mesh size was chosen to achieve both optimum precision requirement and a reduction in computational time and resources.This is because mesh size greatly influences the accuracy of CFD results during computational calculation.Finally,computational fluid dynamics(CFD)method was used to compare the effect of different bending angles of the mixing vanes(MV)to the heat transfer performance of fuel assembly,and a reference optimal bending angle of mixing vane was obtained.Based on this,the influence of springs,dimples and different arrangement of mixing vanes on the flow heat transfer of rod bundle channel was analyzed and studied.In the reactor core,fuel rods have different spatial power distribution along different sections,heights on the same fuel rod.Also,based on the different location of the fuel rod in the fuel assembly,the fuel rod may have different power distribution.However,in this numerical research,a single spacer grid was used to provide a simplified approximation of even and un-even power distribution in the MV radial section of fuel rod,influence of different vanes bending angle on the heat exchange performance of fuel components.In addition,to investigate the influence of installation springs,dimples,different mix vanes configuration mode on the axial and radial power distribution.