Behaviour of Ruthenium Oxide Particles in the Two-Phase System of the First Extraction Cycle of the PUREX Process

Abstract

In the PUREX process, extraction disturbances are caused by the formation, at the aqueous/organic interface, of a cumbersome stable emulsion, called “interfacial crud”, stabilized by solid products. These solids are insoluble residues of fission products and precipitates. The effect of insoluble residues, on crud phenomenon, was investigated using submicronic particles of ruthenium (N) oxide in a 3 M nitric acid/30% TBP-dodecane system under electron irradiations. It was shown that irradiation strongly modifies the behaviour of these particles which were gradually collected at the aqueous/organic interface with increasing radiation doses. Such a behaviour can be assigned to a chemical modification of ruthenium (IV) into nitrosyl ruthenium (III) species which is likely to increase the affinity of the irradiated ruthenium oxide particles for the organic phase. However, these particles were not effective in stabilizing emulsions. Thus, the presence of both ruthenium oxide particles and zirconium precipitates has been studied. In such conditions, a bulky and very stable emulsion, whose characteristics are very similar to those of industrial crud, was for the first time obtained. Therefore, the critical condition of crud formation seems to be the simultaneous presence of precipitates and insoluble residues at the aqueous/organic interface.

KEYWORDS:

• interfacial crud
• emulsions
• insoluble residues
• fission products
• electron beams
• irradiation
• radiation doses
• radiolysis
• ruthenium oxides
• nitrosyl ruthenium
• PUREX process
• TBP
• zirconium