New Degreasing Formulations for the Decontamination of Solid Substrates, Consistent With Concentration and Vitrification Process of the Final Wastes

Abstract

Decontamination facilities use various techniques to decontaminate solid substrates. The aim of these facilities is either to recover the substrate for a future second life, or to sufficiently lower the radioactivity level in order to reduce the final volume of high activity waste. One of these techniques remains in aqueous bathes under ultrasonic agitation. This technique is very suitable for the decontamination of small metallic pieces. Most of those pieces are covered with various greases or organic oils very resistant to classical aqueous washes. Thus, this oily layer contains some unfixed radionuclides that must be removed to reach the aimed decontamination factor. This urged decontamination facilities operating staff to consider additive molecules necessary to render aqueous washes consistent with such a contamination. These molecules, namely surfactants, act on the liquid surface to increase affinity between aqueous and oily phases. The surfactant formulations commonly used in French decontamination facilities are standard industrial formulations (F1, F2). Those formulations are generally designed by international manufacturers to be consistent with several applications. Thus, there isn’t any specific formulation fitted to nuclear applications. Today, according to potential modification of the final wastes conditioning matrix (for instance glass matrix instead of bitumen matrix), this standard formulations use could move to the use of some dedicated formulations for nuclear use. The glass matrix and related effluents concentration process required effluents with controlled chemical composition with regard to the presence of radionuclides. However, the composition of the industrial formulations used until today are not precisely known (according to trade secret), and sometimes can contain molecules unfitted to the final waste vitrification process. For instance, some sodium silicates are used to bring basic properties to the surfactant formulations whereas this kind of compounds is quite inappropriate to the concentration process (possible formation of gel in nitric acid with high concentration of silicates). The present study deals with the potential replacement of these industrial formulations by other ones with controlled chemical composition and concentration. Each new formulation consists of an assembly of well-known surfactants. The first stage of this study involves the degreasing power evaluation for every formulation. Solid and liquid greases detachment is assessed thanks to different techniques. For instance, the study of liquid greases detachment is achieved thanks to a CCD camera. The contact angle between the solid substrate and the grease is followed up during the degreasing step. This allows us to draw degreasing kinetics so as to compare the formulation effectiveness including industrial ones. The second stage of this work presents decontamination factor achieved during real operations with the new designed formulations. These tests were performed in an industrial decontamination facility and the efficiency of the new formulations is compared to the standard industrial ones.