Research On The Performance Of PWR Core Via CFD Analysis

To optimize the design and ensure the safety & economy of a nuclear reactor core,the deep insight of the nuclear thermal-hydraulic mechanism should be obtained.Then the regularities can be summarized and utilized.In addition,the effective cooling of the reactor core,the power uprate,and the extension of the lifetime will also be realized easily.However,the system and sub-channel analysis codes are widely used in the current thermal-hydraulic analysis.These codes belong to the large scale codes.The resolution of their meshes are still very course.Furthermore,they also rely on the experimental correlations,semi-empirical correlations,and assumptions with big safety margin.Therefore,it is difficult to reflect the status and regularity of the single phase,two phase,swirling flow,turbulence flow,flow mixing,velocity gradient,temperature gradient,and other key physical parameters in a fuel spacer grid,mixing vane,and other complex structures in a reactor core.The small scale analysis is in great need to catch the distribution of the flow velocity,pressure,temperature,and other key parameters for the thermal-hydraulic analysis.Meanwhile,the small scale analysis also supplies the fine thermal-hydraulic date for the neutron physics,chemical curd& corrosion,irradiation damage,flow-induced vibration,and other multi-physical processes in reactor core.Then the whole lifetime performance of a reactor core can be understood deeply.The computational fluid dynamic(CFD)analysis technology can catch the small scale characteristics of geometry,flow,and heat transfer.That means CFD analysis can supply the detailed information for the thermal-hydraulic analysis.However,the CFD mesh resolution is much higher,the cell number is also in great need,and the quality of CFD analysis is closely related with the multi-physical data feedback.Therefore,this research has been carried out to resolve the these problems.This research is based on the analysis and utilization of the thermal-hydraulic characteristics,it is also based on the discovery and application of the CFD regularities,and its main focuses are as follows.(1)Research on the applicability and efficiency of the CFD analysis for PWR core,which contains: 1)Establishment of the quantitative estimation scheme for the efficiency of CFD analysis.This research focus is used to compare the efficiency of the CFD schemes in theinternational scope,then it can guide the scheme design and choice for the CFD analysis.2)Establishment of the suitable and efficient CFD meshing schemes for the typical structures of PWR core.This research focus is used to test different mesh types(such as tetrahedron,polyhedron,triangular prism,quadrangular prism,polygon prism,etc.)for the typical structures of PWR core(such as mixing vane,dimple,spring,etc.),then it can suggest the suitable and efficient meshing schemes to save the computing resources and time.3)Establishment of the suitable and efficient turbulence computing schemes.This research focus tried the hybrid application of multiple turbulence models in a CFD analysis,then it can apply the optimal turbulence model for each local region of a PWR core,which can improve the analysis suitability and save the computing resources & time.4)Establishment of the simplified CFD scheme for the thermal-hydraulic analysis.This research focus is used to realize a further improvement of the efficiency.(2)Research on the optimization for the design of thermal-hydraulic experimentsTo optimize the experimental design and the application of the experimental data,reduce/modify the experimental errors from the experimental solid boundaries to the lateral flow,turbulence flow,flow resistance,etc.,and choose the suitable experimental domains(fuel bundles like 3×3,5×5,etc.),this research has done some work to analyze the effect from the flow boundaries and domain sizes to the thermal-hydraulic status.Some regularities have been found,and they were used to design the utilization of the experimental data and the experimental domain size.(3)Research on the multi-scale application of CFD analysisThe improvement of the accuracy of the high-scale thermal-hydraulic analysis can improve the accuracy of the local boundary for the CFD analysis,then the CFD analysis will be more suitable for the thermal-hydraulic status of the local research region in a PWR core.Therefore,some work was done to optimize the high-scale thermal-hydraulic models from the CFD analysis.In the research,sub-channel code was chosen as the example of the high-scale code,and the flow mixing status and regularities were summarized for the lateral flow between the adjacent sub-channels,adjacent parts in one assembly,and adjacent parts between two assemblies.(4)Research on the multi-physical application of CFD analysisThe consideration of the interactions between the thermal-hydraulic status and other physical statuses(such as neutron physics,fuel performance,chemistry,mechanics,etc.)can obtain the multi-physical feedbacks to improve the suitability of the CFD analysis for the real performance in a PWR core.Some work was done to realize the mesh mapping and data transfer in the parallel computing condition for the thermal-hydraulic filed and neutron physical filed.These two fields are just as the representation for the research of the coupling technology.The coupling technology can also be suitable for other physical fields,because the differences in mesh type,mesh size,mesh arrangement are the general problems for the multi-physics in PWR core.In addition,the influence from the meshing schemes and data transfer are also analyzed for the coupling computation,and some regularities have been found.