A Sol-Gel Process for Preparing Dense Forms of PuO₂

A sol-gel process for preparing dense microspheres of PuO₂ was developed. The process has three major operations: 1) preparation of an aqueous sol; 2) removal of water to give solid gel particles; and 3) calcination at controlled conditions to remove volatiles and to sinter to a high density at relatively low temperatures (1100 to 1200°C). The plutonia sol is prepared by precipitating the hydrous oxide from a nitrate solution with ammonium hydroxide. After it is washed, the hydrous oxide is peptized by the addition of nitric acid to give a nitrate-rich plutonia sol containing a nitrate/plutonium ratio of 1. The nitrate concentration is lowered by drying and baking the sol. The residue is then resuspended in water to give a dilute sol, which is concentrated by evaporation to the desired plutonium concentration. The sols produced by this procedure are 1 to 3 M in plutonium concentration and have / Pu mole ratios of 0.1 to 0.15. They are stable for several months and compatible with low-nitrate thorium and uranium sols. Dense homogeneous microspheres of plutonia, plutonia-urania, and plutonia-thoria have been produced at desired ratios on a pilot plant scale.