Detailed thermal modelling of the ALLEGRO ceramic assembly

Abstract

Gas-Cooled Fast reactor (GFR) is one of the favourable Generation IV type concepts under development. ALLEGRO reactor will be a demonstrator reactor of this gas-cooled fast reactor technology. Compared to conventional gas-cooled reactors in the case of a GFR reactor the power density is one order of magnitude higher, and the high temperature fuel assemblies are cooled by a low-density coolant (He), therefore special attention is paid to the heat transfer and heat removal performance of the reactor.The topic of this paper is the detailed CFD investigation of the temperature distribution of a GFR reactor concept’s fuel assembly. The developed CFD models describe the one-sixth segment of the ALLEGRO hexagonal ceramic fuel assembly. ANSYS CFX17 was used to perform the simulations. The first models had been developed to describe the velocity distributions in the bare rod bundle. The bare rod bundle models provided precise inlet boundary conditions for the active length models. With the full active length models, the flow and the temperature distributions have been evaluated. The slight asymmetries of the cladding temperature distributions and the locations of the temperature maximums have been specified. The effect of the heat conduction in the structural elements and the heat radiation were also taken into account. The more complex models gave more precise results, but with increasing computational efforts. Modelling the radiative heat transfer increased the accuracy of the calculations.