Numerical prediction of flow and heat transfer in a loosely spaced bare rod bundle

A wall-resolved Large Eddy Simulation (LES) is performed for a loosely packed bare rod bundle with Reynolds number of 54,650. The simulation includes heat transfer in a liquid metal with the Prandtl number of 0.016. The rod bundle configuration corresponds to the ALFRED lead-cooled reactor design. The ALFRED design employs nuclear fuel assemblies with triangular arrangement of the fuel rods. In the present study, two important thermal-hydraulics aspects of the ALFRED rod bundle configuration have been analysed. Firstly, the proposed design should not lead to any undesirable vibration issues and, secondly, the heat transport should assure sufficient cooling with no hot spots. The obtained flow and thermal fields are analysed and compared with available data. A detailed investigation of the flow field has revealed the existence of a relatively weak gap vortex street in the loosely packed rod bundle. Hence, this considered configuration is unlikely to cause any vibration issues. In addition, the observed thermal field has shown a specific logarithmic trend, representing the heat transfer in wall bounded flow configurations for a wide range of Péclet numbers. In general, no hot-spots are observed for the considered design parameters.