Research on Thermal Diffusion Performance of Fuel Assembly Spacer Grid Based on Numerical Methodology

As one of the most important parameters in subchannel analysis codes used in core thermal-hydraulic design, Thermal Diffusion Coefficient (TDC) is generally acquired by single phase thermal-hydraulic tests, which are costly in time and economy. Based on the mechanism and model of the turbulent mixing, this paper expounds the simulation method of TDC in subchannel code, corrects the problem that TDC was obtained only by temperature field calculation in the past, and puts forward the thermal diffusion factor that characterize the temperature exchange between hot and cold channels. As a result, the whole TDC evaluation method based on CFD technology is formed, and the simulation results are compared to the test results. The results of comparative analysis show that the relative deviation between the results of numerical method and the experimental results is less than 10%, which are in good agreement. Considering certain conservative punishment, it can basically replace the related experiments and greatly improve the efficiency of design and development. Besides, the influences on the TDC of relative parameters, such as thermal hydraulic conditions, grid structure, number of grids, grid spacing, are analyzed. The results demonstrate that the TDC characteristics of fuel assemblies are largely related to the grid structure, and are less affected by thermal parameters.