Optimal ferro frit for leaching stability of radioactive metal oxide sludges-based solidified body

Abstract

In nuclear power plants, the corrosion of metallic components exposed to radioactive liquid waste and coolant can result in the formation of sludge. This study examined the optimization of ferro frit additives to enhance the leaching stability of solidified radioactive sludge. Specifically, simulated sludge, composed of Fe₂O₃, Cr₂O₃, NiO, and Co, was solidified using various additives—including ferro frit 3110, ferro frit 3195, and B₂O₃—and evaluated for leaching stability under ANSI/ANS 16.1 conditions. Among the four target elements, Fe, Ni, and Co consistently demonstrated excellent leaching resistance, while Cr required further immobilization. Co, a key nuclide in leaching resistance assessments for radioactive waste disposal, exhibited low leachate concentrations under all tested conditions. The addition of B₂O₃-rich frits substantially improved Cr leaching resistance by strengthening the glass network structure and suppressing ionic mobility. This improvement is attributed to B₂O₃'s role in reducing non-bridging oxygen content and increasing network polymerization. As the Cr₂O₃ and NiO content in the sludge increased, the sintering temperature required for stable solidification rose from 950 to 1050 °C. These findings demonstrate that producing chemically durable solidified radioactive sludge suitable for final disposal requires both thermal and compositional optimization, particularly through the incorporation of B₂O₃.