Thermo-Hydraulic Analysis of a LFR Generation IV Reactor with a Porous Medium Approach

This paper analyzes the stationary behaviour of the LFR European reactor design ELSY with a porous medium approach by computing the three-dimensional average distribution of temperature, pressure and velocity fields. Knowledge of these physical quantities is of particular importance for the computation of reactor reactivity and heat stresses on the fuel structural elements. The numerical simulations of the flow in the lower and upper plena of the reactor are performed with a FEM code that solves the full three-dimensional set of the incompressible Navier-Stokes equations with energy and turbulence model. Due to the reactor huge size the code uses a simple LES (Large Eddy Simulation) turbulence model for the viscosity which takes into account the turbulence vorticity effects at scales greater than the typical grid spacing. In the core region the reactor complexity requires the adoption of a spatial scale greater than the assembly transverse dimension. This approximation implies the reduction of the core to a sort of {it porous medium} through which the lead coolant flows at the subchannel level. This approach leads to a two-scale model where the phenomena that occur at the high-resolution level may have impact on the lower resolution.