Changes in the duplex grain structure of UO 2 with a bimodal grain size distribution and irregular grains

Abstract

Grain growth and the transition from irregular to regular grains have been studied on the duplex grain structure of UO 2. The powder compacts were sintered in CO 2 at 1300 and 1500°C for 0.1 to 40 h. The duplex grain structure which consists of fine regular grains and coarse irregular grains develops at 1300°C after 0.1 h. Grain growth occurs preferentially in the cluster of fine regular grains, so that the medium-sized grains of about 7 μm develop. Continued grain growth yields coarse grains, and simultaneously the irregular grain changes into the regular one. The initial bimodal grain size distribution of the duplex grain structure changes eventually into a monomodal distribution via transient bimodal distributions. Factors influencing the changes in the duplex grain structure are discussed.