Heavy-liquid metal heat transfer experiment in a 19-rod bundle with grid spacers

Heavy-liquid metals, such as lead and lead-bismuth eutectic (LBE), are prominent candidate coolants for advanced fast reactor concepts and accelerator-driven systems. The thermal-hydraulic behavior of these fluids in fuel-assembly-representative geometries is a key issue to be further investigated for the development of such systems. Aiming to achieve a better understanding of these complex flows, an experimental campaign has been undertaken at the Karlsruhe Liquid Metal Laboratory (KALLA) in the frame of the European research project THINS (Thermal Hydraulic of Innovative Nuclear Systems, 2010–2014). The experiment consists of an electrically heated 19-pin hexagonal rod bundle cooled by LBE at typical reactor conditions in terms of operating temperature, power density and velocity. This bundle includes three grid-spacers which both keep the rods in position and provide support for detailed temperature measurements at each axial position. In this work, the pressure drop, the average heat transfer coefficients, hot-spot factors and sub-channel center temperature are investigated. It is observed that the first measurement level is still on the thermally developing region, while the other two give similar results to each other and thus belong to the fully developed region. A large degree of confidence on these experimental results derives from their good repeatability within their uncertainties.