Abstract
This paper presents a possible path for developing a RANS (Reynolds Averaged Navier-Stokes simulation) based CFD (Computational Fluid Dynamics) methodology applicable to real scale 217-pin wire wrapped fuel assembly of the KAERI (Korea Atomic Energy Research Institute) PGSFR (Prototype Gen-IV Sodium-cooled Fast Reactor). In this study, a RANS (Reynolds Averaged Navier-Stokes simulation) based CFD (Computational Fluid Dynamics) analysis using the General Grid Interface (GGI) function and innovative grid generation method was implemented in the 7-pin and 37-pin wire-wrapped fuel assembly, which use the general-purpose commercial CFD code, CFX. The RANS based CFD methodology can be successfully extended to the real-scale 217-pin wire-wrapped fuel assembly of the KAERI PGSFR. Complicated and vortical flow phenomena in the wire-wrapped fuel bundles were captured by a shear stress transport (SST) turbulence model, and by a vortex structure identification technique based on the critical point theory. The CFD results show good agreement with the friction factor correlation model, which can consider the number of wire-wrapped pins in the fuel assembly. The wire spacers induce a secondary flow by up to about 16 % of the inlet mean velocity magnitude. The secondary flow in a corner and edge sub-channel is much stronger than that of an interior sub-channel. The axial velocity, which is averaged in the corner and edge sub-channels, is about 30% higher than the axial velocity averaged in the interior sub-channels. Three-dimensional multi-scale vortex structures start to be formed by an interaction between secondary flows around each wire-wrapped pin. Large-scale and small-scale vortex structures are generated in the corner and edge, and the interior sub-channel, respectively. The behavior of the large-scale vortex structures in the corner and edge sub-channel are closely related to the relative position between the hexagonal duct wall and the wire spacer. It is expected that the multi-scale vortex structures in the fuel assembly play a major role in the convective heat transfer characteristics.
