Effect of ammonium diuranate precipitation conditions on the characteristics and sintering behaviour of uranium dioxide

Abstract

AbstractAmmonium diuranate has been prepared by adding aqueous ammonia to uranyl nitrate solution under different conditions of temperature and final pH. The resulting precipitates, when dried, can be considered as loosely bound compounds with an ammonia/uranium ratio of 0.37 containing varying amounts of water and ammonium nitrate. As well as differing in composition these precipitates differ markedly in their specific surface areas. After calcination to U3O8 in argon at 700° and reduction in hydrogen at the same temperature, all the diuranates yield uranium dioxide of similar specific surface, and it is concluded that the calcination temperature is the principal factor in determining this. The powders when milled, mixed with an organic binding agent, granulated, pressed and sintered in hydrogen for 2 h. at 1650° give uranium dioxide compacts with bulk densities greater than 96.5% of the X‐ray density (10.96 g./cm.3). Little, if any, correlation has been found between the precipitation conditions and the sintered densities of the compacts. although a relatively rapid rate of addition of ammonia seems to give a slightly denser compact and it seems possible that some uncontrolled variation during milling or pressing outweighs any effects due to differences between the powders.