Verification and validation considerations regarding the qualification of numerical schemes for LES for dilution problems

Since a long time, the Large Eddy Simulation (LES) concept is considered as a very promising candidate for advanced thermal hydraulic modeling in Nuclear Reactor Safety. This paper shows how LES is successfully applied in an industrial framework to free shear flows at high Reynolds numbers and to the associated transport of scalars (e.g. boron). Extensive verification and validation attempts towards this objective have already been performed for the Trio_U code (Höhne et al., 2006, Bieder et al., 2007 and Bieder and Graffard, 2007). In the first part, this paper presents a short overview of what has been done for predicting the boron concentration at the core inlet under accident conditions. These calculations are then related to the demands of Best Practice Guidelines (BPG), which have been discussed by Mahaffy et al. (2007). It is shown, that high quality LES simulations for free sheer flows can be performed on tetrahedral meshes, what significantly simplifies the mesh generation procedure in topologically complex geometries. Guidelines specifically devoted to the LES framework are proposed to analyse the capability of numerical schemes to treat correctly the scalar transport.