Hwan-Young Kim

ADSORPTION CHARACTERISTICS OF RADIOTOXIC CESIUM AND IODINE FROM LOW-LEVEL LIQUID WASTES

In order to remove the radiotoxic nuclides, Cs+ and I−, from low-level liquid wastes, the adsorption characteristics have been studied using a mixed adsorbent of chabazite zeolite and activated carbon. The equilibrium data of each nuclide were well correlated with the DA equation in the wide range of equilibrium concentrations. The SEM-EDAX analysis provided precise understanding of the adsorption mechanism of each nuclide. A surface diffusion model was applied to estimate the intraparticle mass transfer and provided prediction results acceptable for practical implementation in the liquid waste treatment.

IMMOBILIZATION OF RADIOACTIVE SALT WASTE INTO SILICA-BASED WASTE FORM VIA CHEMICAL CONVERSION

Abstract The molten salt waste from a pryochemical process to recover uranium and transuranic elements is one of the problematic radioactive wastes to be solidified into a durable waste form for its final disposal. This paper suggests a new method as a dechlorination approach to the immobilization of salt waste. The inorganic composite consists of SiO2, Al2O3, and P2O5 (SAP), which can generate a series of reactive sites for metal chlorides when in contact with molten salt. Under an oxidative condition, metal chlorides were successfully dechlorinated and converted into metal aluminosilicate, metal aluminophosphate, and metal orthophosphate, which are manageable at a high temperature. The optimum mixing ratio of SAP/salt in weight is about 2, and a borosilicate glass shows good compatibility with the reaction products containing phosphate compounds. By using a glass, a highly monolithic waste form was successfully fabricated at 1100°C, and more than 33 wt% of mixing ratio of glass as a chemical binder increased the chemical durability of the waste form. Use of SAP as an effective stabilizer can offer a chance to avoid Cl-induced problems and control the vaporization of volatile elements. This allows a high degree of freedom in the fabrication of monolithic waste form.

Characteristics on the SAP-Based Wasteform Containing Radioactive Molten Salt Waste

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, SiO2 -Al2 O3 -P2 O5 (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 (Lix Alx Si1−x O2−x ) and metal phosphate (Li3 PO4 and Cs2 AlP3 O10 ) while alkali earth and rare earth chlorides were changed into only metal phosphates (Sr5 (PO4 )3 Cl and CePO4 ). 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/m2 day. 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.© 2009 ASME