CFD simulation of heated tight-lattice rod bundles for an IAEA benchmark

The International Atomic Energy Agency (IAEA) organizes Coordinated Research Projects (CRP) to facilitate the development and validation of computer codes for design and safety analysis of nuclear power plants. Canadian Nuclear Laboratories (CNL) participated in such a CRP that included Computational Fluid Dynamics (CFD) benchmark exercises for heated rod bundles. This paper presents the CNL benchmark results for the 4 × 4 tight-lattice rod-bundle experiment (pitch-to-diameter ratio P/D = 1.08) performed at Korea Atomic Energy Research Institute (KAERI). The KAERI experiment comprised of upward flows of water through the rod bundle configuration that included twisted-vane spacers and eight support grids along the length of the heated rod bundle. The commercial CFD code STAR-CCM + v 9.02.007 was used to simulate the flow and heat transfer in the entire bundle geometry including the supporting grids and vane spacers. Turbulence was accounted for using a k-ω turbulence model and conjugated heat transfer was included in the analysis to account for the effect of heat conduction on the fuel-rod wall temperature. The CFD predictions were assessed against the experimental data for the circumferential variation of the rod wall temperature at four different axial positions relative to the twisted-vane spacers. It was observed that the CFD model tends to overpredict the wall temperature, and the extent of overprediction is larger at lower measurement positions than at higher measurement positions.