CHARACTERISTICS ON THE SAP-BASED WASTEFORM CONTAINING RADIOACTIVE MOLTEN SALT WASTE

摘要

This study investigated a unique wasteform containing molten salt wastes which are generated from the pyro-process for the spent fuel treatment. Using a conventional sol-gel process, SiO_2-Al_2O_3-P_2O_5 (SAP) inorganic material reactive to metal chlorides were prepared. By using this inorganic composite, a monolithic wasteform were sucessfully fabricated via a simple process, reaction at 650°C and sintering at 1100°C. This unique wasteform should be qualified if it meets the requirements for final disposal. For this reasons, this paper characterized its chemical durability, physical properties, morphology and etc. In the SAP, there are three kinds of chains, Si-O-Si as a main chain, Si-O-Al as a side chain and Al-O-P/P-O-P as a reactive chain. Alkali metal chlorides were converted into metal aluminosilicate(Li_xAl_xSi_(1-x)O_(2-x)) and metal phosphate(Li_3PO_4 and Cs_2AlP_3O_(10)) while alkali earth and rare earth chlorides were changed into only metal phosphates (Sr_5(PO_4)_3Cl and CePO_4). These reaction products were compatible to borosilicate glasses which were functioned as a chemical binder for metal aluminosilicate and a physical binder for metal phosphates. By these phenomena, the wasteform was formed homogenously above μm scale. This would affect the leaching behaviors of each radionuclides or component of binder. The leach rates of Cs and Sr under the PCT-A test condition were about 10~(-3)g/m~2day. The physical properties (Cp, k, ρ, Hv, and etc) were very reasonable. Other leaching tests (ISO, MCC-1P) are on-going. From these results, it could be concluded that SAP can be considered as an effective stabilizer on metal chlorides and the method using SAP will give a chance to minimize the waste volume for the final disposal of salt wastes through further researches.