ROLE OF O/U RATIO ON SINTERING OF UO2

The sintering of UO2 is a volume diffusion controlled process. The sintering rate as a function of the concentration of hyperstoichiometrie oxygen at the sintering temperature shows the influence of the O/U ratio on the effective uranium diffusion coefficient. Except under atmospheres having a low oxygen capacity, a sintering specimen is in equilibrium with the furnace atmosphere which can therefore be used to set the sample stoichiometry. The resulting diffusion coefficients of stoichiometric material determined from the rate of initial shrinkage of powder compacts are in good agreement with values determined directly from tracer studies. Hyperstoichiometric specimens (O/U= 2.02) show an enhancement of the shrinkage rate and hence the effective uranium diffusion coefficient is several orders of magnitude greater than expected from published diffusion coefficients. © 1969.