Characteristics of solidified products containing radioactive molten salt waste

For a treatment of molten salt wastes generated from a pyro-processing of oxide spent fuel, we had suggested a stable chemical route, named GRSS (Gel-Route Stabilization and 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 90 wt% LiCl, 6.8 wt% CsCl, and 3.2 wt% 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 1100 deg. C after mixing with borosilicate glass powder, where the salt loadings were about 16-20 wt%. The solidified products had a density of 2.3-2.35 g/cm3, a micro-hardness of 4.69-4.72 GPa, a glass transition temperature of 528-537 deg. C, and a thermal expansion coefficient of 1.65 X 10-7-3.38 X 10-5 deg. C. Leaching results by the PCT-A method revealed leached rates, 10-3-10-2 g/m2 day and 10-4-10-3 g/m2 day for Cs and Sr, respectively. From the long-term ISO leaching test, the 900 day-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. (authors)