Thermal-hydraulic study on the VHELP rod bundle of China initiative accelerator driven system

Wire-wrapped rod bundles are candidate fuel assembly forms for the Lead–Bismuth Eutectic (LBE) cooled reactor of China initiative Accelerator Driven System (CiADS). The hydraulic experiment of the 19-rod bundle has been completed on the Visual Hydraulic Experimental Loop Platform (VHELP) of CiADS. It is necessary to study the thermal–hydraulic behavior of VHELP 19-rod bundles, providing a reference for the safety design of CiADS. Since the wire structure forces the LBE coolant having low Prandtl number heat transfer characteristics to cross mixing in the channel, a turbulent heat transfer model that can simulate reasonably the Reynolds stress and Reynolds heat flux is needed in the numerical calculation. In the present work, an isotropic four-equation model, which considers the difference between the velocity field and the temperature field of LBE and allows simple zero-fixed-value boundary conditions to be imposed on the wall for turbulent kinetic energy k and its dissipation rate ε∼, temperature fluctuation kθ and its dissipation rate εθ∼, was applied to investigate the heat transfer phenomenon of VHELP rod bundles in CiADS project. Firstly, the flow pressure drop characteristics with different Reynolds numbers of the VHELP rod bundles were studied. The pressure drop data predicted by the present isotropic four-equation model agrees with the Cheng and Todreas relation but is higher than the hydraulic experimental results of unheated wire-wrapped rod bundles for the CiADS-VHELP project. Finally, the effects of flow rates and heat fluxes on the detailed thermal–hydraulic behavior of VHELP rod bundles with seven pitches were quantitatively analyzed. This study can reference the design and experimental project of the LBE-cooled wire-wrapped fuel assembly in CiADS.