A pre-test CFD analysis has been performed for the new Fuel bundle experiment to be carried out in the CIRCE facility. For a fixed pitch to diameter ratio of 1.8, fully developed and 3D analysis are presented for the elementary subchannel. The full 3D subchannel with non-active zones and spacer grids is simulated to study the entry effects and the local perturbation induced by the grid. The thermal peaking factor and the pressure loss induced by the central spacer grid is also evaluated.

In liquid metals, due to the low Prandtl number, the thermal boundary layer is much larger than the mechanical one, and therefore the bulk temperature does not coincide with the central channel temperature. On the basis of computational results, the ‘correct’ heat transfer coefficient based on wall temperature and bulk temperature is compared with the practical experimental measurement evaluation based on wall-thermocouples and central channel temperature. Moreover, The realistic non-uniform heat flux of the pins is taken into account in order to evaluate the local variation of heat transfer coefficient and temperature due to this effect.

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