The Study of Pre-Oxidation and Low Temperature Sintering Mechanism to Uo2+x Pellets

Abstract

Uranium dioxide powders were surface pre-oxidation treated. Phases and properties of the powders after pre-oxidation treatment were investigated by DSC-TG、XRD、BET and Dilatometer. The results show that there is a little of U3O7 in uranium dioxide powders by pre-oxidation treatment at 240°C for 8h in air, UO2 powders will transform into U3O8 at 382°C for 8h in air. The shrinkage temperature of the uranium dioxide pellets after pre-oxidation treatment decreased from 1200°C to 580°C, densification rate (ΔL/L) increased also from 1.52×10-4/K to 3.08×10-4/K. The mechanism of low temperature sintering to pre-oxidation UO2+x pellets was explained by simplified point defect model and densification equation. The UO2+x diffusion coefficient, , is much higher than which of UO2. The densification equation is expressed by , and the factor A is according to , a=16.23658, b=0.04247 and c=-2.18802×10-5.