The sintering of open and closed porosity in UO₂

Abstract

High green density UO₂ powder compacts were annealed over a range of temperatures to establish the sintering mechanisms for open and closed porosity. During the intermediate stage of sintering the interconnected porosity was found to sinter at a rate consistent with a volume diffusion process dependent on the instantaneous grain size. The apparent activation energy for open pore sintering was significantly higher than that for volume or grain boundary diffusion, this being attributed to systematic differences resulting from the grain growth process. The fraction of closed porosity increased to a maximum with the collapse of the open porosity then decreased during the final stage of sintering.