Iodine Immobilization by Sodalite Waste Form
- PDF / 258,923 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 7 Downloads / 213 Views
Iodine Immobilization by Sodalite Waste Form T. Nakazawa1, H. Kato1, K. Okada1, S. Ueta1 and M. Mihara2 1 Mitsubishi Materials Corporation, Energy & Ecosystem Laboratories, Ibaraki, 311-0102, JAPAN, E-mail: [email protected] 2 Japan Nuclear Cycle Development Institute, Tokai Works, Ibaraki, 319-1194, JAPAN ABSTRACT Leachabilities and solubilities of the synthesized iodide sodalite and natural (chloride) sodalite were measured by leach test. The iodide sodalite was synthesized in nitrogen gas flow at 800°C for 2 hours. The crystalline structure of the product was certified by XRD analysis. The natural sodalite containing chlorine was obtained at Bancroft, Canada. The several types of solution were used to evaluate the influence of the solubility of sodalite that included the varied pH and the chemical compositions. The solubilities of chloride sodalite were calculated by the thermodynamics data. The solubility measured for the synthesized iodide sodalite was compared with that calculated. The solubility of the synthesized iodide sodalite was approximately 2 x 10-4 mol/L, which shows a good agreement with the calculated one of the natural sodalite. INTRODUCTION Iodine-129 is one of the most critical nuclides from the point of view of reprocessing waste disposal in Japan. The radiological half-life of I-129 is approximately 16M years, which is too long to disintegrate in the disposal repository. Additionally the sorptivity of iodide on geological materials are very low and I-129 might migrate rapidly from a disposal facility to the surface through geological layer. Silver iodide is one of the candidate chemical forms of iodide reprocessing waste because of its excellent stability in an atmospheric condition. However it is known to decompose to metallic silver and iodide in reducing conditions. Waste forms that can stably contain iodine therefore need to be developed in order to reduce the impact of I-129 on the safety assessment of disposal. Sodalite is naturally occurring mineral, which contains chlorine in the aluminosilicate cage structure. It is reported that the sodalite is synthesized easily from clay minerals such as kaolin [1] or some chemical reagents [2] in the study of immobilization of iodine from reprocessing and solidification of halide salt waste from pyrochemical reprocessing. Leachability of sodalite in aqueous solution is comparatively low [1-4]. The characteristics of sodalite are favorable to meet the condition proposed in the safety assessment that iodine release is restricted by the solubility limit [5]. In this paper, the procedure to synthesize iodide sodalite and the dissolution behaviors of the synthesized product are presented.
EXPERIMENTAL Material Two types of sodalite were used in leach test. The first was the synthesized iodide sodalite, which was treated in nitrogen gas flow at 800°C for 2 hours. The second was the natural sodalite containing chlorine provided by Iwamoto Mineral Co. Ltd, which was obtained at Bancroft, Canada. Sodalite [Na8(AlSiO4)6Cl2] contains halogens, mainly
Data Loading...
