ANALYTICAL STUDY ON EFFECTS OF BWR FUEL SPACER ON DROPLET DEPOSITION

In a boiling water nuclear reactor (BWR), liquid film dryout may occur on a fuel rod surface when the fuel assembly power exceeds the critic al power. The spacers supporting fuel rods affect on the thermal-hydra ulic performance of the fuel assembly. The spacer is designed to enhan ce critical power significantly. If spacer effects for two-phase flow could be estimated analytically, the cost and time for the development of the advanced BWR fuel would be certainly decreased. The final goal of this study is to be able to analytically predict the critical powe r of a new BWR fuel assembly without any thermal-hydraulic tests. Init ially, we developed the finite element code to estimate spacer effects on the droplet deposition. Then, using the developed code, the spacer effects were estimated for various spacer geometries in a plane chann el and one subchannel of BWR fuel bundle. The estimated results of the spacer effects showed a possibility to analytically predict the criti cal power of a BWR fuel assembly. (C) 1997 Elsevier Science S.A.