CFD Investigation of Heat Transfer in Supercritical Water-Cooled Flow Through 3×3 Fuel Rod Bundles

Abstract

CFD investigation of heat transfer in supercritical water-cooled flow through fuel rod bundles has been carried out, using commercial software STAR-CD 4.02 with specific ad hoc user routines for modeling physical property of supercritical water. The configuration considered is a typical core assembly of 3×3 fuel rod (round tube) bundles inside solid square box, as seen in the nuclear reactor. After priori mesh convergence studies, investigations are focused on key characteristics of flow and heat transfer performance, notably the wall temperature distributions, the mass flux and the secondary flow patterns in the cross-section. It is found that the rod wall temperature distributions exhibit highly non-uniform feature near the domain exit with very high wall temperatures: about 625°C observed on the corner rod and about 562.5°C on the border rod, respectively. It is believed that the appearance of the extremely wall temperature may be related to the non-uniform distributions of mass flux in the cross-section of the bundles as the low mass flux co-existing with the high wall temperature. Further analysis of the secondary flow in the cross-section reveals wider spectrum of vortex flow structures, more complicated than previously noted by the sub-channel analysis. To verify the influence of turbulence models on the secondary flow, both linear and non-linear k-ε models are applied and results are quite similar. This finding indicates that the cause of the secondary (cross) flow might not be solely due to the anisotropic property of turbulence as suggested by other researchers. The present 3D CFD study provides more complete database of 3×3 rod bundle flows and will be useful to improve the industry practice of applying the sub-channel analysis.