A multiscale heat transfer model for nuclear reactor assemblies

We develop a new multiscale approach to investigate the heat transfer in a nuclear assembly. Fuel rods are represented as mono-dimensional (1D) inclusions into a three-dimensional (3D) bulk domain representing the coolant. More precisely, the interaction between the fuel rod grid and the coolant is modeled by means of projection operators that couple the 1D and 3D problem taking into account the actual dimension of the rods together with the cladding layers. Due to the dimensional reduction, the inclusions do not need to conform with the bulk computational grid. As a result, the computational challenges of the numerical discretization, due to the high geometrical complexity of the problem, are significantly reduced, as confirmed by the numerical simulations presented in this work.