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Effects of cement and iron corrosion products on the durability of buffer material in geological disposal of HLW

水泥和铁腐蚀产物对高放废物地质处置缓冲材料耐久性的影响

基本信息

批准号：
13680584
负责人：
SATO Seichi
金额：
$ 2.24万
依托单位：
Hokkaido University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13680584/
关键词：
radioactive waste cement bentonite iron corrosion products geological disposal diffusion 収着

项目摘要

For the safety assessment of the geological disposal of high-level radioactive waste, a fundamental study on the long-term durability of bentonite buffer was made from the viewpoint of the alterations of Na-bentonite that would occur after disposal.Fe-bentonite is one of alteration products caused by the corrosion of overpack. In this study, Fe-bentonite was prepared from Na-bentonite in an oxygen-free glove-box by contacting Na-bentonite with FeCl_2 solution, and characterized by various analytical methods such as selective dissolution method, mossbauer spectroscopy and X-ray diffraction method. An oxidized Fe-bentonite sample was prepared by exposing Fe-bentonite to air, and also characterized in the same way. It was found that divalent cations, Fe^<2+>, were the predominant exchangeable cations in Fe-bentonite, and they were gradually oxidized when the sample was exposed to air. In batch sorption experiments, the higher sorption coefficients of Se(IV) and Se(VI) were obtained for Fe-bentonite and oxidized Fe-bentonite than for Na-type.Another alteration product is Ca-bentonite that would be generated by Ca^<2+> ions from the dissolution of cement materials in a waste repository. In this study, apparent diffusion coefficients of Na^+ and Ca^<2+> were determined for the mixture samples of Na-and Ca-bentonite at various diffusion temperatures. The salinity effect on the diffusion coefficient of Na^+ ions was also studied for Na-bentonite. It was indicated that the effects of Ca-bentonite and salinity on the apparent diffusion were not remarkable. However, significant effects of the salinity on the activation energy for diffusion were found. The change in the activation energy can be explained by the diffusion model in which the predominant diffusion process is considered to change as the salinity increases.

为了对高放废物地质处置的安全性进行评价，从钠基膨润土在处置后可能发生的蚀变角度出发，对膨润土缓冲剂的长期耐久性进行了基础性研究，铁基膨润土是外包装腐蚀产生的蚀变产物之一。本研究以钠基膨润土为原料，在无氧手套箱中，用FeCl_2溶液与钠基膨润土接触制备了铁基膨润土，并采用选择溶解法、穆斯堡尔谱和X射线衍射等方法对铁基膨润土进行了表征。通过将铁基膨润土暴露于空气中制备氧化铁基膨润土样品，并以同样的方式表征。结果表明，铁基膨润土中的主要交换性阳离子为二价阳离子Fe^<2+>，在空气中暴露后，二价阳离子逐渐被氧化。在静态吸附实验中，铁基膨润土和氧化铁基膨润土对Se（IV）和Se（VI）的吸附系数高于钠基膨润土，另一种蚀变产物是钙基膨润土，它是由废弃物处置库中水泥材料溶解产生的Ca^2+离子所形成的。本文测定了Na^+和Ca^<2+>在不同扩散温度下的表观扩散系数。研究了盐度对钠基膨润土中Na^+离子扩散系数的影响。结果表明，钙基膨润土和盐度对表观扩散的影响不显著。然而，显着的盐度对扩散激活能的影响被发现。激活能的变化可以解释的扩散模型，其中的主要扩散过程被认为是随着盐度的增加而改变。