RADIOISOTOPES

Large amounts of high-activity-level contaminated water were generated from the nuclear accident of Fukushima Dai-ichi Nuclear Power Plant caused by the Great East Japan Earthquake. At present, the cold shutdown is completed by cooling system, while large amounts of contaminated (>500,000 m³) are still stored. This paper deals with the selective decontamination properties of Cs⁺ and Sr²⁺ by using inorganic adsorbents: zeolites, insoluble ferrocyanides, crystalline silicotitanates, and potassium titanates. Zeolites have three important abilities; (1) high selectivity for Cs⁺ and Sr²⁺, (2) Cs gas trapping ability, and (3) self-sintering ability. As for multi-nuclides adsorbability, mordenite, chabazite, ferrierite and clinoptilolite group have strong adsorbability for Cs⁺, and A-type and X-type zeolites for Sr²⁺ in seawater. Other zeolites, such as L-type zeolite and Ag⁺ adsorbed zeolites (A-type and X-type zeolites), have high decontamination abilities for actinoids and radioactive I⁻ions, respectively. Stable ceramic solidification of secondary solid wastes can be accomplished by using the above trapping and sintering abilities; mixing and sintering with zeolites are effective for the stable Cs immobilization and lowering of Cs leachability.