Fragmentation of Uranium Dioxide after Molten Uranium Dioxide-Sodium Interaction

Abstract

A series of 30 runs were performed to gain information on the fragmentation of molten UO2when dropped into a bath of liquid sodium. In this experiment, hollow cylindrical UO2 pellets were heated with electric current fed to a tungsten rod, passed through to center hole. The resulting molten UO2 dripped down its fall into the sodium bath. High-speed cinematography (500~2,000 frames/sec) was utilized to observe the fragmentation of the UO2 droplets upon its impact with the sodium surface. Records were taken of the changes in pressure and temperature induced in the sodium bath by the impact of the U2 droplets. The physical characteristics of the solid U2 particles resulting from the quench were examined for particle size distribution, particle shape and surface condition, as well as microstructure, to gain an insight into the mechanism of fragmentation. It is concluded from the study that, for the purpose of Fuel Coolant Interaction (FCI) analysis, the U2 particles can be assumed to be spherical in shape and to have log-normal particle-size distribution. The density function in terms of particle weight, representing the finest particle-size distribution, can be expressed on the basis of presently available empirical data, by , D: Diameter of U2 particle in microns.