Rapid immobilization of cesium in radioactive molten salt waste via supercritical water hydrothermal synthesis

Abstract To swiftly address Cs presence in radioactive molten salt waste, we utilized nonradioactive CsCl to simulate 137 CsCl. Through supercritical water hydrothermal synthesis with metakaolin, we converted it to pollucite and sodalite within 10 min. With Cs/Al and Si/Al mole ratios set at 0.4 and 2.0, respectively, the primary phase in the solidified form was predominantly pollucite, with CsCl solubility reaching 25.52 wt.%. All elements were uniformly distributed within the solidified form. Additionally, the supercritical water hydrothermal synthesis not only aided CsCl immobilization but also improved the chemical stability of the solidified form. The normalized leaching rate of Cs after 28 days is less than 4.03 × 10 −6 g m −2 day −1 , which is much lower than the existing solidification substrate. This investigation presents a fresh approach to the rapid disposal of radioactive molten salt waste.