In the dynamic core of nuclear pebble bed reactors, the prediction of the fluid flow within the packing determines the heat transfer characteristics and, hence, the performance of these reactors.

The fluid flow of the gas phase can be characterized and quantified in terms of the pressure drop coefficient. Therefore, in this work, the pressure drop in a packed pebble bed having different aspect ratios (ratio of the diameter of the bed to the diameter of the pebbles) has been measured experimentally in a separate-effects pilot-plant scale and cold-flow experimental setup of 0.3 m in diameter using a differential pressure transducer technique. The effects of superficial gas velocity have been investigated using a range of velocities from 0.01 to 2 m/s covering both the laminar and turbulent flow regimes. In addition, the effect of bed structure (aspect ratio) on the pressure drop coefficient has been investigated for the studied packed pebble bed. The results show the strong dependence of the pressure drop on both the aspect ratio and, hence, the porosity of the bed and the coolant gas velocity. The obtained experimental results have been used to evaluate the predictions of the correlations recommended for pressure drop estimation in packed pebble bed nuclear reactors. The present work provides insight on the pressure drop and fluid flow of the gas phase in the studied bed using an advanced technique and methodology.