Abstract
The steam flow distribution above the mixture level in the reactor core of a pressurized water reactor (PWR) during a small break loss of coolant accident is investigated using a Computational Fluid Dynamics (CFD) code. This is an exploratory study to assess impacts of non-uniform power distribution, spacer grids and cladding ballooning on the subchannel steam flow. The study examines the single phase flow distribution of steam in non-uniform power sub-channels. A fine mesh calculation describes the resulting flow distribution due to non-uniform power and shows buoyancy driven chimney effects in the hot channel. The study then investigates the impact of spacer grids on the non-uniform steam flow distributions. The paper evaluates the magnitude of the mixing caused by the flow turbulence past the grid and the distortion caused by the grids on the buoyancy driven chimney flows. Finally the study evaluates the effect of cladding ballooning and blockage on the non-uniform single phase steam flow distribution. The significance of blockage vs. increased buoyancy driven chimney flow at the blockage and above is evaluated.
