Recycling metal waste in nuclear decommissioning by advanced phosphoric acid decontamination process

The heavy burden of nuclear waste is currently the driver for the development of advanced technologies for treatment and conditioning of radioactive materials. Nuclear decommissioning generates a huge quantity of contaminated metal scraps to be managed. An advanced PHADEC-based process is under study to obtain further volume savings of the final waste and recycle metallic materials after treatment. This process consists of phosphoric acid dissolution of the superficial contaminated layer, subsequent oxidation of the pickling solution, electrochemical precipitation and vitrification of the dried iron phosphate precipitate. The research activity aims to optimize the electrochemical precipitation and separation steps to produce a suitable precipitate for the following vitrification unit. Pickling, oxidation and precipitation tests were performed at lab and intermediate scale. Stable Co, Cs, Sr and Ni were chosen as representatives of the radionuclides of the metallic dissolution liquor. To enhance decontamination and recycle the pickling solution in a pilot plant, screening tests were conducted thus exploring the potential role of co-precipitation agents in the electrochemical precipitation step. A promising abatement of contaminants from the phosphoric solution was observed by adding 0.3 M BaSO4 during the electrochemical precipitation. Ongoing activities point to improve the decontamination yields by testing more co-precipitation agents.