CFD Simulation on Turbulent Flow in Tight Lattice Fuel Assemblies

In this paper, URANS (Unsteady Reynolds Averaged Navier Stokes) methodology was applied to the prediction of turbulent flow inside tight lattice rod bundles with different P/D ratios, i.e. from 1.001 to 1.2. The turbulent flow with Reynolds number ranging from 5 000 to 215 000 was investigated by analysing the bulk velocity, wall shear stress and turbulent intensity distributions in the subchannel. The results show significant effect of P/D on stream wise velocity and wall shear stress in very tight lattice (P/D<1.1). The results also indicate that the mixing factor (Y) has an inverse proportion relation to δ/D, even though δ/D is smaller than 0.011. When Reynolds number reaches certain value in tight lattice, the bulk velocity and wall shear stress are less sensitive to Reynolds number.