title: Characteristics of wasteform composing of phosphate and silicate to immobilize radioactive waste salts.
abstract: In the radioactive waste management, metal chloride wastes from a pyrochemical process is one of problematic wastes not directly applicable to a conventional solidification process. Different from a use of minerals or a specific phosphate glass for immobilizing radioactive waste salts, our research group applied an inorganic composite, SAP (SiO(2)-Al(2)O(3)-P(2)O(5)), to stabilize them by dechlorination. From this method, a unique wasteform composing of phosphate and silicate could be fabricated. This study described the characteristic of the wasteform on the morphology, chemical durability, and some physical properties. The wasteform has a unique "domain-matrix" structure which would be attributed to the incompatibility between silicate and phosphate glass. At higher amounts of chemical binder, "P-rich phase encapsulated by Si-rich phase" was a dominant morphology, but it was changed to be Si-rich phase encapsulated by P-rich phase at a lower amount of binder. The domain and subdomain size in the wasteform was about 0.5-2 μm and hundreds of nm, respectively. The chemical durability of wasteform was confirmed by various leaching test methods (PCT-A, ISO dynamic leaching test, and MCC-1). From the leaching tests, it was found that the P-rich phase had ten times lower leach-resistance than the Si-rich phase. The leach rates of Cs and Sr in the wasteform were about 10(-3)g/m(2)· day, and the leached fractions of them were about 0.04% and 0.06% at 357 days, respectively. Using this method, we could stabilize and solidify the waste salt to form a monolithic wasteform with good leach-resistance. Also, the decrease of waste volume by the dechlorination approach would be beneficial in the final disposal cost, compared with the present immobilization methods for waste salt.
authors.affiliation: Advanced Fuel Cycle Development, Korea Atomic Energy Research Institute, 150 Deokjin-dong, Yuseong-gu, Daejeon 305-353, Korea. hspark72@kaeri.re.kr
authors.forename: Hwan-Seo
authors.initials: HS
authors.lastname: Park
authors.forename: In-Hak
authors.initials: IH
authors.lastname: Cho
authors.forename: Hee Chul
authors.initials: HC
authors.lastname: Eun
authors.forename: In-Tae
authors.initials: IT
authors.lastname: Kim
authors.forename: Yong Zun
authors.initials: YZ
authors.lastname: Cho
authors.forename: Han-Soo
authors.initials: HS
authors.lastname: Lee
mesh_terms: D007700:Kinetics; D010710:Phosphates / Q000737:chemistry*; D011850:Radioactive Waste / Q000032:analysis*; D012492:Salts / Q000737:chemistry; D017640:Silicates / Q000737:chemistry*; D014501:Uranium / Q000737:chemistry*; D018505:Waste Management / Q000379:methods*
chemical_list: D010710:Phosphates; D011850:Radioactive Waste; D012492:Salts; D017640:Silicates; D014501:Uranium