Abstract: The time and cost for the analysis and design can be decreased greatly by using of Calculation Fluid Dynamic （CFD） methodology in thermal performance analysis of fuel assemble and the design of spacer grid. In the middle of 1990s, the commercial CFD code has been used to analyze the 3D flow and temperature fields of the fuel in foreign countries. It was successful to design the spacer grid with the verified methodology. In the Laboratory of Bubble Physics and Natural Circulation, the CFX code was employed to calculate the fluid field of a rod bundle with spacers in the end of 1990s. The structure simulation of complex small size geometry, the selection of the proper boundary conditions and the evaluation of CFX applicability have been studied and problems were solved. Then the calculation of flow field of the single-phase and air-water two-phase has been carried out and compared with experiment results. The steam-water two-phase flow has been studied and the design of new spacer has been carried out. It is desired to develop a CFD analysis and design methodology, which can predict not only the flow and temperature fields in rod bundle with spacers, but also the surface temperature of the rods.
The results show that it can compare the turbulence, eddy and fluid temperature near rod of single-phase flow to evaluate the mixing characteristics of a spacer to fluid. The spring and dimple of the spacer have evidently effect on flow and it is necessary to simulate. In order to ensure the correctness of prediction results, it suggests to take a benchmark exercise before the analysis of CFD thermal hydraulic analysis for a fuel assemble with spacers.