Development of a new process for the radioactive ion exchange resins conditioning - HYPEX ®

A novel process, HYPEX®, for the conditioning of radioactive ion-exchange resins (IEXs), has been developed and is presented here. The process involves the immobilization of radioactive IEXs into a geopolymer matrix after grounding down to a micrometer scale and a complete hydration. The studied geopolymers are based on metakaolin and activated by an alkali solution. The effects of ~ 90 different combinations of the structural atomic ratios in the geopolymer, such as silicon/ aluminum (Si/Al) and water/aluminum (H2O/Al), on macroscopic mechanical properties were examined, aiming at identifying the most suitable geopolymer for the conditioning of spent resins. Two geopolymer formulations were selected, both utilizing a fully sodium-based alkali solution and enriched with calcium hydroxide and siliceous inert filler to enhance their mechanical properties. One formulation involves the use of sodium silicate, while the other incorporates silica fume. Fractions of 20%wt and 30%wt of treated resin were added to the selected geopolymer matrices, and several tests were carried out in accordance with the Italian Safety Criteria for the Management of Radioactive Waste as far as resistance to compression, water immersion, thermal cycles, radiation, leachability, fire, and gas permeability are concerned. It is demonstrated here that HYPEX® satisfies the stringent Italian Criteria, even when 30%wt of resin is embedded.