Two-step alkaline thorium dioxide precipitation A low waste method for highly sinterable ThO 2

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 ThO 2 filters quickly and calcines to crystalline ThO 2 at low temper- atures. As-precipitated ThO 2 contains significant quantities of adsorbed H 2 O and CO 2 , 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.