The influence of precipitation conditions on the properties of ammonium diuranate and uranium dioxide powders

Continuous precipitation in one and two stages was investigated to determine the effect of precipi nation variables on the properties of ADU precipitates and the sinterability of subsequent UO₂ powders in pellet fabrication. The pH at which precipitation occurred was the most important parameter in determining the size of ADU agglomerates and the settling rate and filterability of the slurry. In two-stage precipitation, the ADU properties were determined by the proportion of uranium precipitated at different pH values. Washing nitrate from ADU appeared not to affect the properties of the subsequent UO₂ pswder but a significant decrease in filterability occurred when the ADU was extensively washed. When ADU was reduced to UO₂ at 600 °C the agglomerate structure of the ADU was retained. The larger the agglomerates in the UO₂ powder (lower pH of precipitation of precursor ADU) the less sinterable it was; pseudomorphs of large agglomerates were still discernible in the sintered pellets. Thus settling rate of the ADU slurry gave an early indication of the likely sinterability of the resultant UO₂ powder since both were functions of agglomerate size.