Thermal-hydraulic effect of wire spacer in a wire-wrapped fuel bundles for SFR

The computational fluid dynamics (CFD) investigation is carried out over the full-scale experimental facility of SIENA's 7-pin fuel assembly using commercial CFD code, CFX. The purpose of this research is to understand the effect of wire spacer on flow and temperature fields in fuel bundle by comparing the CFD analysis with wire spacer and without wire spacer. Thermal-hydraulic phenomena in a fuel bundle have been investigated by Reynolds Averaged Navier-Stokes (RANS) flow simulation based on the shear stress transport (SST) turbulence model. Calculated pressure drop in the fuel bundle agrees well with Cheng & Todreas model. When the turbulent Prandtl number in the CFD analysis is adopted with 0.02, Nusselt number of the CFD analysis results has a good agreement with Mikityuk model, Graber and Rieger model, and Borishanski et al. model. Based on the CFD investigation, the wire spacers locally induce a tangential flow by up to about 13% of the axial velocity. The tangential flow in the corner and edge sub-channels is much stronger than that in the interior sub-channels. The flow with a high tangential velocity is periodically rotating in a period of wire lead pitch. Pressure drop value without wire spacer is about 6% less than that with wire spacer over the various range of Reynolds number. The cross flow due to the wire spacer can achieve to enhance heat transfer characteristics up to about 50%. Furthermore, the wake regions due to helically wrapped wire spacers are developed nearby the counter rotating position of wire spacers. These wake regions have the peak temperatures in the sub-channels. In this analysis case, we found that the temperature uncertainty of sub-channel is about 5% of temperature difference between inlet and outlet of the test section.