Numerical Investigation Of Impact Caused By Spacer Grid To Flow And Heat Transfer In Fuel Assemblies

The thermal hydraulic performance of the reactor core mostly depends on the spacer grid in the fuel assemblies. The development of independent and localization fuel assemblies may need totally understand the impacts to flow and heat transfer in fuel assemblies caused by spacer girds. Compared to the experimental tests which are long and costly, CFD has become one of the most important research methods as its safety and rapidity. Using CFD method to analyze flow and heat transfer characteristics in fuel assemblies has become more and more valuable in engineering issues.Relevant literatures about flow and heat transfer in fuel assemblies were reviewed. The main research contents were determined based on the current study process. First of all, numerical analysis methods of modeling of a typical5×5rod bundles were introduced, including simplification of the geometry, generation of the mesh and its sensitive analyses. Secondly, the performance of various turbulence models, including eddy viscosity models and Reynolds stress models, were evaluated. At last, impacts caused by feature structure and mixing vane to flow and heat transfer characteristics were achieved.Based on above research contents, three calculation models have been built including single-span spring and dimple model, single-span simplification model and multy-span model. After a reasonable simplification to the geometric model, numerical mesh was generated using ICEM software. Flow features, pressure drop and Nu numbers were calculated using ANSYS CFX. Three dimensionless factors including swirl factor, cross-flow factor and turbulence intensity factor were introduced to describe the complex flow field characteristics further. The proper turbulence models to simulate flow and heat transfer in rod bundles were suggested based on the comparison to the similar experimental results. The results of one-span model indicate the spring and dimple may improve the cross flow and heat transfer, as well as the pressure drop. Flow features and heat transfer of multi-span model were obtained. In the discussion of the impact caused by mixing vane, different bending angles and two different types of mixing vane were simulated. The research results provide a detailed technique support and data reference to the development of independent and localization fuel assemblies.