Study on the Effects of Mixing Vane Configurations on Flow Field in Rod Bundle

Abstract

In most PWR designs, spacer grids are proposed to keep the fuel rods in fixed positions. Mixing vane grids (MVGs) contribute to inter-subchannel mixing as well as providing structural support, which has been demonstrated by both experiments and numerical simulations. The mixing vane configurations in the MVGs have significant influence on flow redistribution. The mixing vane configurations will lead to flow redistribution among neighboring subchannels. Appropriate mixing vane configuration designs in the MVG will result in expected flow redistribution coupled with the power distribution of the rod bundle. This paper analyzes the effects of different types of mixing vane configurations in the MVGs on the flow field in the 5×5 rod bundle using the improved mixing vane grid model in the subchannel code. In the improved model, source terms related to the MVGs performance were developed and some geometrical parameters of mixing vanes (such as the length, angle, area and configurations of the mixing vanes) were examined and brought in to improve the capability of subchannel code in predicting actual MVGs performance. This paper gives a brief introduction to both the original spacer grid model and the improved mixing vane grid model in subchannel analysis, and focuses on analysis of the effects of the mixing vane configurations. In this paper, different types of mixing vane configurations are considered for the comparison of hydraulic performance in the 5×5 rod bundle under uniform axial heating conditions. The calculation results applying the original model are also presented for the comparison analysis, and the calculation results without the MVGs are provided as the basis of the comparison. Both the qualitative and quantitative analyses are presented, and the hydraulic performance of different types of mixing vane configurations are evaluated. The analysis indicates that the improved MVG model can reflect the mixing vane configuration information, and could provide a reference for mixing vane configuration designs in the MVG as well as the experimental design related to the MVG performance study.