A New Solvent Extraction Process for Preparing PuO₂ Sols

A new solvent extraction process for preparing PuO₂ sols was developed. The process has three major operations:

1. extraction of HNO₃ from Pu(NO₃)₄-HNO₃ feed with a long-chain alcohol, such as n-hexanol, until a plutonia sol with a NO₃^-/Pu mole ratio of ∼1 is obtained
2. seeding, in which sol is added to the feed solution before or during extraction to create a micelle structure of aggregated crystallites
3. thermal denitration, which consists of drying and baking the sol.

The aggregated micelle structure promotes rapid denitration and crystallite growth; because these sols denitrate very rapidly and are insensitive to overheating, denitration can be accomplished by a variety of continuous processing methods. As a result, low nitrate sols ( /Pu mole ratio = 0.1 to 0.2) with average crystallite diameters of 60 to 70 Å are easily prepared. The sols produced by this method can be converted to dense microspheres, shards, or sinterable powders. The sols can also be mixed with urania or thoria sols in any proportion and used to prepare microspheres, shards, or powders which are of interest for use in the fabrication of nuclear reactor fuels. These sols, therefore, have all the versatility of application of sols prepared by earlier methods. In addition, considerable advantages are obtained with regard to method of preparation and ease of scale-up.