Development of a new surfactant liquid formulation for TBP removal in reprocessing plants for decommissioning purposes

CEA has developed in the past years surfactant liquid solutions to remove organic matter located at the surfaces of nuclear components used in reprocessing facilities. These components may be covered with Tributyl Phosphate or products resulting from TBP radiolysis like Dibutyl phosphate or Monobutyl phosphate. These molecules can be combined either with uranium, plutonium or metal ions like zirconium for example. Conventional treatment used for decontamination usually have poor degreasing effect (like sodium hydroxide) so few of these products can be removed successfully. The aim of developing these new treatments is to achieve a better degreasing effect and eliminate sodium ions from the secondary liquid wastes. In a first step, low alkaline formulations have been developed (sodium content about 0,5 M to 1 M). In a second step, it is aimed to remove sodium ions completely, together with keeping a high degreasing efficiency. Another advantage to remove sodium hydroxide from decontamination solutions is to avoid Pu precipitation during the decontamination process. This paper describes the study of a degreasing formulation based on the use of fully soluble low foaming surfactants in nitric acid medium. One presents laboratory scale experiments, experiments on active samples, liquid secondary waste processing, a scale one experiment, and associated basic studies. In conclusion, chemical properties of a surfactant solution in nitric acid medium have been detailed. Aim of the formulation was to remove TBP molecules from metallic surfaces. Efficiency of the treatment was evaluated on inactive and hot samples and compared to more conventional treatments like concentrated sodium hydroxide and pure nitric acid. A micellization of 5,3 g/L of TBP in 0,5 M nitric acid is obtained. This value is about 15 times larger than TBP solubility in acid. The efficiency was found to be higher than that of sodium hydroxide and consequently the risk of Pu and U insolubilization is eliminated by working in acidic conditions. Moreover, secondary liquid wastes can be easily addressed to the vitrification unit as they contain no sodium ions. A pretreatment including oxidation with peroxide hydrogen and evaporation has been further validated. The scale one experiment is being now set up at the Pilot Reprocessing Facility in Marcoule. In the future, it is aimed to benefit from this experiment in the frame of larger scale decommissioning projects. In parallel to these industrial objectives, basic studies have been launched together with Montpellier University to get a better understanding of basic phenomena involved in the TBP solubilization