Input model of a VVER 440/213 fuel assembly and CFD calculations by the FLUENT code

The preparation of the final version of the computation network of a VVER 440/213 fuel assembly by the GAMBIT code is described. Qualified estimates of the size of the networks (numbers of cells) are made especially in dependence on the network density in the transverse section. Some sensitivity analyses performed on smaller geometries, devoted to the effect of computation network density on turbulence modelling and to the effect of the limiting layer thickness on the temperature and flow rate fields are described. Of importance was the analysis of spacer grid replacement by means of the porous media function with regard to savings in the number of computational cells. The CFD calculations in the FLUENT code, performed first for smaller test problems and subsequently for large problems describing 1/6 to 1/2 of the fuel assembly, are described. Analyzed are the coolant distribution within the assembly after passing the bottom supporting plate and the effect of the spacer grids on coolant distribution and on heat transfer