Effect of Particle Size Distribution of UO₂ Powder on Sinterability

Abstract

Nuclear grade UO₂ pellets are produced worldwide through very well proven powder metallurgy route involving operations like granulation, final compaction and sintering, in which particle size distribution of the UO₂ powder plays an important role in final pellet quality. Virgin UO₂ powder produced through ADU route is fine in nature and has poor flowability. Granulation operation is carried out to improve its flowability. During final compaction, higher fraction of granules yield poorly packed green compacts whereas excess of fines lead to increased inter-particle friction. Hence, a judicial mix of fines (45-250 µm) and granules (> 250 µm) is very important for obtaining the stipulated mechanical strength, density and dimensional control of the sintered pellets. In the present work, the weight fraction of granules and fines were varied to study the effect of particle size distribution of UO₂ powder on sintering quality, onset of sintering, sintering rate, linear shrinkage, grain size etc. using a high temperature dilatometer under reducing atmosphere. Variation of grain size with respect to the sintering environment has also been studied.