Two-step alkaline thorium dioxide precipitation A low waste method for highly sinterable ThO2

Abstract We precipitated thorium in a two-step process with ammonia and carbonates. In contrast to single step ammonia or carbonate precipitation, the two-step process precipitates >99.9% of Th and removes >99.5% of Ra alongside. Filterability is strongly affected by pH variations in the ammonia step, and under well-controlled conditions, the precipitated ThO2 filters quickly and calcines to crystalline ThO2 at low temperatures. As-precipitated ThO2 contains significant quantities of adsorbed H2O and CO2, which are removed during calcination. The calcination temperature greatly affects the green density of produced pellets, but for all calcination temperatures investigated, the sintered densities are in excess of 96% with grain sizes within the range applied for nuclear fuels at 10–16 μm.