CFD investigations of the flow in a 5x5 rod bundle with mixing vane spacer grid were performed with single-phase and two-phase flow conditions. A non-linear k-epsilon model was used to simulate secondary flow and non-isotropic turbulence. A detailed analysis of the results showed that mixing vane induced swirling flow strongly affects the cross-flow. A model was developed to predict the forced cross-flow between the sub-channels and implemented into the sub-channel analysis code COBRA-FLX
