Analysis of inter-channel sweeping flow in wire wrapped 19-rod bundle

Helical wire spacers are widely used in sodium cooled fast reactors. One of the main effects of wire spacers is enhancing the inter-channel cross flow in triangular arrayed rod bundles. To study the characteristic of sweeping flow rate across the gaps between the sub-channels, the computational fluid dynamics (CFD) method is used in the present study to analyze the flow field in a 19-rod bundle with wire wraps. This CFD work only considers the fluid zone of one section of the rod bundle. The height of the CFD model with periodic inlet and outlet boundary conditions is one wire pitch. The k-omega SST model is used as the turbulent model. The wire effect on the velocity distribution of the flow across the interface between two sub-channels is investigated in the CFD study. Based on the force balance equation between the wire wake force and the surface friction force of rods in the circumferential direction, a theoretical model for estimating the average swirling flow rate driven by one single wire is proposed. The simulation shows that the ratio of rod pitch (P) to rod diameter (D) has a strong effect on the velocity of the sweeping flow. The flow rate increases with the P/D ratio. The simulation agrees well with the proposed model. In addition, the effect of the ratio of wire pitch (H) to rod diameter has also an influence on the cross flow rate: A small H/D ratio leads to higher cross flow rate. A correlation as a function of both P/D ratio and H /D ratio is proposed to predict the sweeping flow velocity by the present study.