HYPEX®: A New Process for the Treatment and Conditioning of Radioactive Ion-Exchange Resins

HYPEX ®a is a new process for the treatment and conditioning of radioactive ion-exchange resins (IEXs), developed by the company green-land in Italy. Spent resins constitute the major waste volume produced in the nuclear industry which must be properly treated and conditioned. When conditioned for disposal, the physical and chemical properties of the resins tend to deteriorate and weaken the solid matrix, making their conditioning a major issue. On top of that, the existing technologies for ion-exchange resin disposal increase a lot the final waste volume or involve high temperature treatments: the first aspect affects the cost, while the second aspect increase the hazard in a radioactive environment. In this contest, HYPEX® aims to be a low-cost process, simple to implement industrially, embedding high quantities of resin with high safety. The HYPEX® process consists in the incorporation at room temperature of radioactive IEXs, previously grinded down to micrometre scale and fully hydrated, in a new special geopolymer matrix. To develop HYPEX®, a wide investigation of the most suitable geopolymers was first carried out, aimed at identifying the best geopolymers formulations from the point of view of its macroscopic mechanical properties. The chosen geopolymers are metakaolin-based, activated with a sodium-based alkali solution. The response to geopolymer fundamental atomic ratios variation (for instance Si/Al, Na/Al and H2O/Al), and to different amount of resin, has been studied, also improving the matrix wettability and reducing voids, by proper mixing of the components under vacuum conditions before solidification. Several hundred samples were produced with different geopolymer formulation, resin content and paste preparation methodology (with or without vacuum conditions), to identify the optimal combination of these factors. Resistance to compression, resistance to thermal cycles, resistance to irradiation, resistance to water immersion, leachability, gaseous permeability and inflammability were measured on the samples. The tests were carried out according to the test procedure highlighted in the Technical Guide #33, drafted by Italian Nuclear Safety Authority, which determines the Safety criteria for the management of radioactive waste in Italy. The test results demonstrated that up to 30%wt of resin can be conditioned with the novel HYPEX® process, exceeding in performance all the thresholds’ values imposed by Italian Regulatory. HYPEX® promises to be a game changer in the solution of the problems linked to ion-exchange resin conditioning in nuclear power plants. On the one side it reduces the amount of the final waste volume with respect to the use of conventional matrices. On the other side, its main features of complying with the Safety Requirements, while still keeping the process at room temperature, makes it strongly easily implementable at industrial level.