CFD Study on Mixing in VVER-440 Fuel Rod Bundle With Guiding Vanes in Spacer Grids

In this article, we study mixing in a fuel rod bundle geometry used in VVER-440 type pressurized water reactors. The flow inside the fuel assembly under normal operation is simulated using the FLUENT 6.3 computational fluid dynamics (CFD) solver. Steady state one phase Reynolds-averaged Navier-Stokes modeling is applied with two-equation turbulence models. In the first part of the article, grid independence is studied using a small submodel of the fuel rod bundle. In the second part, flow across a full-length fuel rod bundle is simulated both with constant temperature and with prescribed heat fluxes at the rod walls. Finally, in the third part of the article, we study how guiding vanes included in the spacer grids would enhance mixing in the hottest subchannels. We propose that having four guiding vanes on each side of the hexagonal spacer grid would produce most mixing in the desired locations of the fuel rod bundle.