Crud Formation in the Purex and Thorex Processes

In the solvent extraction processes for reprocessing spent nuclear fuel, operational flow problems may be caused by the formation of stable emulsions, commonly called “crud.” Our experiments have demonstrated that crud is generated by finely dispersed solids. Such fines can be produced by precipitation of zirconium with degradation products of tributyl phosphate. Experiments show that crud can also be produced by other solids, however, viz., finely divided silica and bentonite. Therefore, fines present in the aqueous feed solution might also produce crud. A special problem arises in the reextraction step in the Thorex process, where a precipitate of thorium dibutyl phosphate causes crud formation.