Characteristics of Solidified Products Containing Radioactive Molten Salt Waste

For a treatment of molten salt wastes generated from a pyroprocessing of oxide spent fuel, we had suggested a stable chemical route, named GRSS (Gel-Route Stabilization & Solidification), and a subsequent consolidation method. By using this method, a series of monolithic wasteforms with different conditions were fabricated, and then their physicochemical properties were investigated. A simulated salt containing 90wt% LiCl, 6.8wt% CsCl, and 3.2wt% SrCl₂ was treated with a gel-forming material system, Si/Al/P = 0.4/0.4/0.2 and 0.35/0.35/0.3, and the gel-products were treated at 1100C° after mixing with borosilicate glass powder, where the salt loadings were about 16∼20wt%. The solidified products had a density of 2.3∼2.35g/cm³, a micro-hardness of 4.69∼4.72GPa, a glass transition temperature of 528∼537C°, and a thermal expansion coefficient of 1.65×10⁻⁷∼3.38×10⁻⁵/C°. Leaching results by the PCT-A method revealed leached rates, 10⁻³∼10⁻²g/m²day and 10⁻⁴∼10⁻³g/m²day for Cs and Sr, respectively. From the long-term ISO leaching test, the 900day-leached fraction of Cs and Sr predicted by a semi-empirical model were 0.89% and 0.39%. The leaching behaviors indicated that Cs would be immobilized into a Si-rich phase while Sr would be in a P-rich phase. The experimental results revealed that the GRSS method could be an alternative method for a solidification of radioactive molten salt wastes.