Speaker
Description
Radioactive sludge wastes generated during reactor decontamination and dismantling are complex matrices containing metal oxides, silica, carbonates, carbonaceous phases, and radionuclides such as Cs, Sr, and Co. To solidify such diverse and complex waste streams, geopolymers (GP) have emerged as a low-carbon-emitting, less porous, and robust alternative to conventional cementitious materials. They are increasingly studied as engineered barriers for cationic, anionic, redox-sensitive, and organic wastes.
In this work, a series of samples with 0, 10, 20, 30, 40, 50, and 60 wt% incorporated simulated decommissioning sludge waste to metakaolin-based geopolymer were synthesized to optimize waste loading. We investigated the physico-mechanical performance of developed waste forms against waste loading at room temperature (21 days) and at 60 °C (5 days). Initially, the apparent density, porosity, and compressive strength were used as primary performance indicators for all samples. Phase composition, microstructure, and chemical characteristics were analyzed using XRD, SEM-EDS, XRF, FTIR, and BET techniques.
The two curing regimes produced almost similar phases (BaCO3, BaSO4, and MnO2) across all decommissioning waste loadings. However, samples cured at room temperature exhibited lower compressive strength (30.91 ± 2.26 to 5.92 ± 0.98 MPa) compared to 60 °C cured samples (39.95 ± 4.66 to 8.05 ±1.28 MPa), likely due to slower reaction kinetics. In both cases, the apparent density increased almost linearly with increasing waste loading, attributed to the incorporation of heavier constituents, pore filling, and enhanced matrix compactness. Based on the physico-mechanical performance, a waste loading of 50 wt% relative to the total waste-form mass appears to be optimal for subsequent radionuclide incorporation and further characterization.
These preliminary results highlight the potential of geopolymers as durable, low-carbon waste forms for immobilizing complex radioactive sludge wastes. Ongoing studies focus on reducing the water-to-binder ratio, incorporating simulated corrosion products, and evaluating long-term leaching behavior.
Acknowledgements
This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Climate, Energy & Environment (MCEE) of the Republic of Korea (No. RS-2023-00236697) and by the National Research Foundation of Korea (NRF) grant funded by the Korea Government Ministry of Science and ICT (RS-2025-02311305).