Session: 08-05: Computational Fluid Dynamics (CFD) and Applications - V

Paper Number: 135170

135170 - Numerical Simulation Study on Axial Mixing Characteristics of Fuel Assembly 

Abstract: 

Because the power in the reactor is distributed in cosine, the CHF is usually not located at the exit. In order to accurately predict the CHF point and increase the accuracy of the reactor safety analysis, it is necessary to conduct in-depth research on the axial mixing coefficient distribution of the fuel assembly. This study used the CFD method to investigate the flow mixing of the rod bundle and spacer grid of fuel assembly. Establish a geometric model for the rod bundle and spacer grid, select the SST model for calculation, complete the mesh sensitivity analysis, and obtain the temperature distribution of sub-channel at different axial positions under rated operating conditions. Using the sub-channel analysis program in conjunction with numerical simulation data, determine the mixing coefficients at different axial positions of rod bundle and spacer grid. The calculation results of the rod bundle indicate that if the mixing phenomenon at the entrance is considered as local mixing, it can be observed that as the influence of local mixing weakens, the mixing coefficient shows a trend of approaching 0 as the axial length increases. There is no significant difference in the axial mixing coefficient calculated by selecting 16 central channels and selecting all subchannels. The mixing at the entrance is caused by the development of the thermal boundary layer, not by the flow distribution at the entrance. The calculation results of the spacer grid show that the cell type spacer grid has an enhanced effect on the flow mixing of fuel assembly. The mixing coefficient is obviously higher at the front end of the heating segment than at the same position of the rod bundle. As the influence of the cell type spacer grid is weakened, the variation of the mixing coefficient along the axial direction is the same as that of the rod bundle.  The strip type spacer grid inhibited the flow mixing of fuel assembly. Specifically, at the front end of the heating segment, the mixing coefficient was significantly lower than that at the same position in the rod bundle. However, due to the influence of the strip type spacer grid, the mixing coefficient at the front end of the heating segment decreased at a lower rate than that in the rod bundle. As the influence of the strip type spacer grid is weakened, the axial variation of the mixing coefficient is the same as that of the rod bundle.

Presenting Author: Junhan Wei China Institute of Atomic Energy

Presenting Author Biography: Zhao Minfu, works at the China Institute of Atomic Energy and is mainly engaged in the research of reactor thermal hydraulic.

Authors:

Xiaoyang Zhang China Institute of Atomic Energy
Junhan Wei China Institute of Atomic Energy
Minfu Zhao China Institute of Atomic Energy