Investigations on the structural evolution and aqueous durability of [Cs Ba ][Fe3+2+Ti4+8-2-]O16 ceramics for radioactive cesium storage

Chemical durability and degradation mechanisms of CsPbI3 as a potential host phase for cesium and iodine sequestration

Effective nuclear waste management of radioactive cesium and off-gas iodine from complex waste streams of used fuels is essential for the sustainable development of advanced nuclear fuel cycles. Once cesium and iodine are separated from their respective waste streams, host phases are required to immobilize them into a durable waste form matrix for long-term disposition. The inorganic metal halide perovskite, CsPbI₃, has a unique crystal structure capable of incorporating both cesium and iodine simultaneously. Exposure to groundwater in geological repositories is a long-term concern for waste forms, as this may cause corrosion and decrease the waste form's ability to retain radionuclides. In this study, we explore the potential of CsPbI₃ perovskite as a promising host phase to incorporate Cs and I, and investigate its chemical durability and degradation mechanisms in an aqueous environment. CsPbI₃ was synthesized through a solution-based method and was consolidated into dense pellets by spark plasma sintering. The chemical durability of the CsPbI₃ pellets was evaluated by static leaching tests in deionized water at different temperatures of 25, 58, and 90 °C. The elemental release mechanisms and surface alteration of the monolithic CsPbI₃ pellets were investigated. Both I and Cs displayed a non-congruent leaching behavior and faster release rates as compared to Pb, particularly at longer leaching durations and higher temperatures. At the initial leaching stage, a PbI₂ alteration layer formed on the surface of the pellet due to the rapid release of Cs and I, followed by the formation of a PbI(OH) alteration layer. The activation energies for both dissolution and diffusion controlled mechanisms were determined to be 44.90 kJ mol⁻¹ and 45.40 kJ mol⁻¹ for Pb, 27.10 kJ mol⁻¹ and 40.82 kJ mol⁻¹ for I and 24.27 kJ mol⁻¹ and 23.86 kJ mol⁻¹ for Cs, respectively. These results show a clear decrease in activation energies from Pb to I and Cs, suggesting a preferential release of I and Cs. The solution-based synthesis of CsPbI₃ as a host phase for Cs and I and the fundamental understanding of the chemical durability and degradation behavior will be useful for further exploring its application for immobilizing iodine and cesium into final durable waste forms for long-term geological disposition.

Elemental release: a CsPbI₃ perovskite pellet is leached in distilled water; post-leaching analysis indicates the formation of PbI₂ and PbI(OH) alteration layers on the pellet surface, and the incongruent release of elements into the leachate.

Rapid solidification of Sr-contaminated soil by consecutive microwave sintering: mechanism and stability evaluation

Consecutive microwave sintering is a method proposed in this study to dispose soil contaminated by Sr during a nuclear accident by rapidly solidifying the contaminated soil. The results show that soil contaminated with 20 wt% SrSO₄ and 30 wt% SrSO₄ can be completely solidified by microwave sintering at 1100-1200 and 1300 ℃, respectively, for 30 min. Sr was found to be cured into slawsonite (SrAl₂Si₂O₈) and glass structures. Moreover, soil sintered at 1300 ℃ has large cured solubility (30 wt.%), good uniformity, and excellent hardness (6.9-7.2 GPa) and chemical durability (below 1.46 × 10^-5 g m^-2 d^-1 at 28 d). Thus, consecutive microwave sintering technology may provide a new method for treating Sr-contaminated soil in case of a nuclear accident emergency.