Numerical simulation on liquid film behaviors in BWR fuel bundle geometry

The spacer effects including the spacer shape, spacer thickness and the clearance are investigated by the 2D calculations with a vertically located upward flow rectangle flow path. The liquid film thickness is strongly influenced by the spacer shape, spacer thickness and clearance too. The thinnest liquid film thickness is observed in the Edge2 type spacer among four assumed spacer shapes in this study. Besides, thicker the spacer thickness and narrower the clearance become, thinner the liquid film thickness becomes. The spatially located obstacles such as spacers, cell stops and springs in the subchannel are evaluated by the 3D calculations. The liquid film thickness would be thinner in the center zone in the subchannel without obstacles, and would be thicker in the gap zone or at the downstream side of obstacles. The calculated circumferential liquid film thickness distribution is compared with the measured for the center rod. Both the measured and calculated results have a good agreements that the thinnest liquid film thickness would appear in the center zone where obstacles are not located in the axial flow path. It can be deduced that the liquid film dryout is mostly likely occurred in such regions. (authors)