Recent advances in immobilization of radioactive cesium and strontium-bearing wastes in alkali activated materials - A review.

This review discusses recent advances in the use of alkali-activated materials (AAMs) to host high heat and radiation-emitting cesium (Cs) and strontium (Sr) wastes. It examines the evolution of geopolymerization, mechanical properties, mineralogy, microstructure, and leaching behavior of Cs-and/or Sr-bearing AAMs, considering their chemical interaction with Cs and Sr nuclides and exposure to temperature and gamma radiation induced by Cs and Sr. The literature indicates that Cs and Sr slightly degrade the mechanical properties of AAMs, with Sr having a more pronounced effect. For AAMs with a low SiO/AlO ratio, decay heat from Cs and Sr can crystallize zeolitic phases, which are beneficial in the short term but detrimental in the long term because of their low stability against gamma radiation. Cs was immobilized via ion exchange within the aluminosilicate phase and Sr mainly by precipitation, but the immobilization of their respective daughter nuclides Ba and Zr was not demonstrated. Gamma radiation exposure does not significantly alter AAM properties, and nitrates in Cs and Sr-bearing wastes reduce gamma-induced water radiolysis. AAMs are promising hosts for Cs and Sr-bearing wastes, but further studies are needed using realistic Cs and Sr waste loading to evaluate the synergistic effects of Cs and Sr chemical behavior, decay heat, and gamma irradiation on the evolution of properties of waste forms, and the ability of AAMs to accommodate daughter nuclides Ba and Zr.