Study on microstructure of clay and its effects on sorption and diffusion behavior of nuclides in geological disposal of nuclear waste

核废料地质处置中粘土微观结构及其对核素吸附和扩散行为的影响研究

• 批准号: 11358007
• 负责人: OHASHI Hiroshi
• 金额: $ 10.69万
• 依托单位: Hokkaido University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (A).
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2000
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11358007/
• 关键词: Atomic force microscope; nuclear waste; montmorillonite; sorption; diffusion; geological disposal; Np

Diffusion behavior of radionuclides in compacted bentonite plays an important role in the performance assessment of bentonite buffer material in geological disposal of high-level radioactive waste. Microstructure of bentonite is considered to be one of the key parameters to affect the diffusion behavior. In this study, therefore, two kinds of montmorillonite(major clay mineral of bentonite)with different particle sizes were prepared, and characterized with several methods. In addition, the diffusion coefficients of HTO, Np(V)ions, Cs^+ ions, Cl^- ions, Ca^<2+> ions and He gas were determined using the montmorillonite samples with different particle sizes and dry densities. It was found that the montmorillonite layers, which compose the montmorillonite particles, have the same size, even if the particle sizes of the samples are different. In addition, the apparent diffusion coefficients of HTO and Cl^- for the fine grained sample were found to be higher tthan for the coarse grained sample at two dry densities, 1.0 and 1.8 Mg m^<-3>, while the opposite particle size effect was observed for Cs^+ ions. These findings cannot be explained by the conventional diffusion model, "pore water diffusion model". The activation energies for diffusion of Np(V), Cl^- and Ca^<2+> ions seemed to be closely related to the basal spacings of the montmorillonite. This suggests the contribution of the diffusion of ions in the interlayer of the montmorillonite. The contribution of a surface diffusion is also suggested for diffusion of Na^+ ions in the mixture of montmorillonite and silica sand. The sorption behavior of Se and Np were studied for Na-and Fe(II)-montmorillonite. The effects of exchangeable cations on the sorption coefficients were found in this study.

放射性核素在压实膨润土中的扩散行为对于高放废物地质处置中膨润土缓冲材料的性能评价具有重要作用。膨润土的微观结构被认为是影响扩散行为的关键参数之一。因此，本研究制备了两种不同粒径的蒙脱石（膨润土的主要粘土矿物），并采用多种方法对其进行了表征。此外，还测定了HTO、Np（V）、Cs^+、Cl^-、Ca^2+和He气体在不同粒径和干密度的蒙脱石中的扩散系数。研究发现，即使样品的粒径不同，构成蒙脱石颗粒的蒙脱石层具有相同的尺寸。此外，在两种干密度（1.0和1.8 Mg m ↑ [2]）下，细颗粒样品的HTO和Cl^-的表观扩散系数均高于粗颗粒样品，<-3>而Cs^+离子的表观扩散系数则相反。这些发现不能用传统的扩散模型--“孔隙水扩散模型”来解释。Np（V）、Cl^-和Ca^2+离子的扩散活化能与蒙脱石层间距密切相关。这表明蒙脱石层间离子扩散的贡献。Na^+离子在蒙脱石和硅砂混合物中的扩散也有表面扩散的贡献。研究了钠基和铁基蒙脱石对硒和氮的吸附行为。研究了交换性阳离子对吸附系数的影响。

项目成果

J.Kozai: "Apparent Diffusion Coefficients and Chemical Species of Neptunium(V) in Compacted Na-montmorillonite"Journal of Contaminant Hydrology. 47. 149-158 (2001)

J.Kozai：“压实钠蒙脱土中镎 (V) 的表观扩散系数和化学形态”污染物水文学杂志。

T.Kozaki: "Diffusion Mechanisin of Chloride Ions in Sodium Montmorillonite"Journal of Contaminant Hydrology. 47. 159-170 (2001)

T.Kozaki：“钠蒙脱土中氯离子的扩散机制”污染物水文学杂志。

Naofumi KOZAI, Yoshifusa ADACHI, Sachi KAWAMURA, Koichi INADA, Tamotsu KOZAKI, Seichi SATO, Hiroshi OHASHI, Toshihiko OHNUKI, Tsunetaka BANBA, Tomihiro KAMIYA and Takuro SAKAI: "Charactrization of Fe-montmorillonite : Overpack Corrosion Products Altering

Naofumi KOZAI、Yoshifusa ADACHI、Sachi KAWAMURA、Koichi INADA、Tamotsu KOZAKI、Seichi SATO、Hiroshi OHASHI、Toshihiko OHNUKI、Tsunetaka BANBA、Tomihiro KAMIYA 和 Takuro SAKAI：“铁蒙脱石的表征：外包装腐蚀产物的改变

T.Higashihara: "Diffusion of Helium and Estimated Diffusion Coefficients of Hydrogen Dissolved in Water-Saturated, Companted Ca-Montmorillonite"Journal of Naclear Fuel Cycle and Environmant. (in press).

T.Higashihara：“水饱和、复合钙蒙脱石中溶解的氦气扩散和氢的估计扩散系数”核燃料循环与环境杂志。

N.Kozai: "Characterization of Fe-montmorillonite : Overpack Corrosion Products Altering of Buffer Materials"Scientific Basis for Nuclear Waste Management. (in press).

N.Kozai：“铁蒙脱石的表征：缓冲材料的外包装腐蚀产物改变”核废物管理的科学基础。