Study of Enhanced Entrance Pressure Losses in a Rod Bundle Experiment Employing Heavy Liquid Metal Coolant

Abstract

Innovative nuclear reactor concepts like accelerator driven systems (ADS) or the lead cooled fast reactor LFR employ lead bismuth eutectic (LBE) as a coolant. Within the framework of the EU project THINS (thermalhydraulics of innovative nuclear systems) a rod bundle experiment in LBE is performed employing characteristic dimensions at the Karlsruhe Liquid Metal Laboratory (KALLA)l of Karlsruhe Institute of Technology (KIT). In a first measurement campaign it is observed that the pressure drop across the first spacer in the rod bundle experiment is noticeable larger than at the subsequent spacers. We speculate that this is due to blockage of the very narrow spacer channels and numerically investigate whether there are substantially enhanced entrance effects. The present numerical study investigates the whole rod bundle including the entrance region in order to show possible mechanisms which can increase the pressure drop of the first spacer even if no blockage is present. The extra pressure loss compared to simulations with uniform inflow is found to be very small which supports the speculation of blockage. Since rod bundle flow is known to depend very sensitive on turbulence models and mesh resolution we carefully verify that our simulations use an adequate computation domain, mesh resolution and turbulence model.