Single-phase computational fluid dynamics applicability for the study of three-dimensional flow in 5′ 5 rod bundles with spacer grids

Abstract

Spacer grids play an important role in pressurized water reactor (PWR) fuel assembly in that they have significant influence on the thermal-hydraulic characteristics of the reactor core. But so far, the numerical studies are performed without regarding dimple and spring of spacer grids, just considering mixing vane. Moreover, these studies use k-ɛ turbulence model without considering the suitability of the other turbulence models upon the different spacer grids flow. A study is carried out to understand the 3-D single-phase flow in AFA-2G 5×5 rod bundles with spacer grids based on numerical method. In order to investigate the suitability of different turbulence models, k-ɛ model and k-ω model, the influence of different parts of spacer grid on the fluid flow is also predicted. By using second-order upwind scheme, hybrid grids technique, and improved SIMPLEC algorithm, the Reynolds averaged mass conservation and momentum conservation equations are solved, and the pressure and velocity field of flow are obtained. The numerical simulation results are compared with experiment results and the agreement is satisfactory. The simulation results show the influences of the spring, dimple and mixing vane, and the different characteristics of the k-ɛ model and k-ω model. Comparing with the experiment results, the simulation results suggest that the k-ω model is suitable for the simulation of the rod bundle flow with spacer grids; the spring and dimple are the main causes of the pressure loss in the spacer grid channel. The friction coefficient of the channel with spring and dimple is 1.5 times the coefficient of the channel with the vane. These results are beneficial to enhance the simulation ability of spacer grids flow and optimization design ability of spaces grid.