Low-temperature sintering with chemically durable glass for selenite solidification

Selenium oxide is highly volatile at high temperatures. This volatility hinders high-temperature processes for immobilizing radioactive selenium-79 (Se-79), resulting in radionuclide loss and secondary waste generation. To overcome this challenge, this study proposes a novel low-temperature sintering method for selenium immobilization. Silver selenite (Ag₂SeO₃) was synthesized and incorporated into a low-melting-point 35Ag₂O-50TeO₂-15 V₂O₅ (ATV) glass matrix. A dense composite waste form was successfully fabricated by uniaxially pressing and sintering a mixture of 10 wt% Ag₂SeO₃ and 90 wt% ATV glass powder at 180 °C, slightly above the glass transition temperature of the ATV glass (T_g = 176 °C). Thermal analysis confirmed that this low-temperature process effectively suppressed Se volatilization. The chemical durability of the sintered body was evaluated using semi-dynamic leaching tests for 120 d in both deionized water (DIW) and synthetic groundwater (Allard water, AW). The waste form demonstrated exceptional leach resistance, with the cumulative fraction of leached selenium remaining below 0.001 % and 0.01 % in DIW and AW, respectively. Surface analysis of the leached samples revealed the formation of a multilayer passivating alteration structure and AgCl precipitation under groundwater conditions, which effectively retarded the release of constituent ions over time. These findings demonstrate that the proposed process mitigates volatilization and secondary waste generation while offering an environmentally robust strategy for managing the long-term hazard of Se-79 in geological disposal.