Mechanistic modeling for ring-type boiling water reactor fuel spacer design (3) run-off effect and model formulation

The fuel spacer is one of the components of a fuel rod bundle and its role is to maintain an appropriate rod-to-rod clearance. The fuel spacer influen ces the liquid film flow distribution in the fuel rod bundle, so that the s pacer geometry has a strong effect on thermal hydraulic characteristics of BWR such as critical power and pressure drop in the fuel bundle. In this pa per, liquid film flow characteristics were experimentally investigated in a circular channel with ring-type spacers using air and water as test fluids in order to be compared with the analytical results introducing the mechan istic spacer model. The spacer model was composed of three effects; the dri ft flow effect, the narrow channel effect and the run-off effect. The drift flow effect and the narrow channel effect were discussed in the previous w orks and the run-off effect is done in this paper. This paper shows the for mulation around the spacer with use of the three effects. The proposed mode l explains well the experimental results of liquid film flow rates and thic kness carried out in reference to the spacer thickness, the gap between the channel wall and the spacer. (C) 2001 Elsevier Science B.V. All rights res erved.