Thermal hydraulic investigations of ALLEGRO ceramic fuel assemblies

Main issue of this paper is to investigate the thermal hydraulics of inner and corner regions of the ceramic assemblies of the GFR demonstrator, ALLEGRO. First, models have been built for bare rod bundle regions to determine the inlet boundary conditions of the complex models. Based on these simulations models have been developed, which include active length ceramic rods with four spacer grids in the regions. These models describe heat convection in the active part of the rod bundles and heat conduction in the clads and assembly shroud. Using these models temperature fields in typical regions are determined and effects of the heat conduction in the clads and thermal radiation are also investigated. Considering the computational effort and accuracy, modelling of the rod cladding and shroud material is required, while modelling of the radiative heat transport is less important.