Enhancing Geopolymer Performance in the HYPEX(R) Conditioning Process for Ion Exchange Resins

Geopolymers are gaining attention as an alternative to Portland cement-based matrices for conditioning radioactive waste due to their superior mechanical properties, chemical stability, and reduced environmental impact. This study investigates the production of geopolymer paste under vacuum conditions to enhance performance and enable higher resin content incorporation. Vacuum processing improves the homogeneity of the composite, ensuring uniform distribution of the geopolymer binder and resin aggregates, which strengthens adhesion and increases compressive strength. However, vacuum conditions may affect paste workability and aggregate segregation, depending on the geopolymer composition. To address these challenges, a design of experiments was conducted to optimize variables such as resin and inert filler content, vacuum intensity, and exposure duration. The optimal combination was identified based on compressive strength, immersion resistance, leachability, and porosity tests. The results demonstrate that incorporating up to 30%wt of spent resin into the HYPEX® geopolymer under vacuum conditions is feasible, achieving compressive strength and immersion resistance exceeding 10 MPa, with a cesium leachability index greater than 7. These properties ensure the structural integrity of the product and significantly reduce the waste volume destined for the National Repository, thus lowering disposal costs. This study highlights the potential of geopolymers as effective conditioning matrices for Low and Intermediate Level radioactive waste.