Assessment of RANS Based CFD Methodology Using JAEA Fuel Assembly Experiment

Abstract

This paper presents an assessment results for the developed 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). 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 JAEA experiment with the 127-pin wire-wrapped fuel assembly. The JAEA experiment study was implemented using water for validating pressure drop formulas in ASFRE code. The edge vortex structures are longitudinally developed, and have a higher axial velocity than corner vortex structures and wakes nearby pins and wires. The wire spacers locally induce a tangential flow by up to about 16 % of the axial velocity. The tangential flow in the corner and edge sub-channels is much stronger than that in the interior subchannels. The large-scale edge vortex structures have higher turbulence intensity and lower vorticity than the small-scale wakes. The corner vortex structures have lower turbulence intensity and vorticity than the small-scale wakes. The driving forces in the X-, Y-, and Z-directions are not only dependent on the axial velocity, but also significantly dependent on the angular position between the wire-spacer and rod, and the relative position between the wire-spacer and duct wall.