Thixotropic corrosive gels for nuclear decontamination

Inspired by an industrial problem, this work consisted in the development of decontamination processes using corrosive gels for the treatment of metallic surfaces. The gels were formulated using a corrosive solution of a strong oxidizing reagent (Ce(IV)) as dissolving agent. This solution was stabilized in a concentrated acidic medium (nitric acid). To obtain a gel from this solution, we used a mineral support (fumed silica) and an organic coviscosing compound (nonionic surfactant). Nuclear requirements were carefully followed. The aim of this project was to prepare thixotropic gels which are liquid under stress (vigorous shaking) to allow an easy splattering, and are solids when stationary to permit strong adhesion to any surface. The study of the rheological properties of these gels was completed by the quantitative as well as qualitative measurements of their corrosive abilities: corrosion control, surface comparison carried out before and after treatment by electron microscopy techniques. The chemical behaviour in solution was also studied, particularly the chemical behaviour of the organic coviscosing agent and the oxidizing reagent. The structure of a by product, (NH4)3Ce2(NO3)9, was determined using powder X-ray diffraction techniques. During the past two years, these processes have been used industrially both in France and abroad. As a conclusion, these industrial results are briefly presented. (author)