General flow sweeping mixing model for subchannel analysis and application to three rod bundles with different typical spacer methods

Abstract

Subchannel analysis is one of the most essential methods in the thermal design of nuclear reactor cores and transient safety analysis. Spacers are arranged to maintain proper geometrical configurations of rod bundles and contribute to crossflow mixing in rod bundles. In this work, a general flow sweeping mixing model is introduced for subchannel analysis, and the model is applicable for rod bundles with arbitrary spacer types. Applications of this model to the mixing vane spacer grid rod bundle, the helical fuel rod bundle, and the wire-wrapped rod bundle are discussed. The degenerate crossflow rates downstream of the mixing vane spacer are accurately predicted, demonstrating the superiority of the GFSM model. When applied to the helical fuel rod bundle, the refined subchannel division approach should be utilized together. The GFSM model can predict twist angle-dependent crossflow rates, showing better agreement with CFD results compared to the existing flow sweeping model. Furthermore, the crossflow rates predicted by the GFSM model in the wire-wrapped rod bundle exhibit higher prediction accuracy. This work provides a new approach to develop the flow sweeping mixing model and unifies the model forms for different rod bundle types.