Development of evaluation for swelling characteristics of bentonite based buffer under water-chemistry condition of high level radioactive waste disposal facility

处理核电站排放的高放射性废物是21世纪需要解决的重要问题。在这个方案中，有一种称为“膨润土基缓冲材料”的材料在多重屏障之一。膨润土基缓冲材料填补了废物容器与周围基岩之间的空间，并且由于废物运输方便，有可能在海岸带附近建造处置设施。本研究旨在定量评价膨润土基缓冲材料在海水条件下的自密封性能，并从海水条件下的自密封性能角度建立膨润土基缓冲材料的设计方法。本研究首先进行了“一维模型自密封试验”，研究了海水条件下的自密封性能。本试验是一种模拟海水状态自密封行为的一维模型试验，通过在一维上设置一个空间，缩小实际处置场地空间部分与缓冲材料的关系，并提供不同浓度的人工海水。其次，具体研究了影响自密封行为的因素，通过测定实验后试样中Na^+、Ca^<2+>、K^+、Mg^<2+>离子的各阳离子交换容量（EXC）和交换阳离子（CEC），考察了海水元素在孔隙水中的侵入情况。此外，在本实验结果的基础上，建立了缓冲材料在蒸馏水条件下的自密封性能预测的经验方程，得到了海水条件下可评价的自密封性能方程和可评价的“膨胀性能方程”。这项研究的新发现如下所示。在以下条件下，通过本试验可知，海水对自密封性能的影响很小。在膨润土A中，如果空间小于1.25mm，供液浓度小于等于海水浓度的100%，则海水的影响很小。而在膨润土B和E中，如果空间小于1.25mm，供液浓度小于等于海水浓度的10%，则海水的影响较小。结果表明，在海水条件下，缓冲材料自密封性能下降较小的原因之一可能是由于海水没有渗透到缓冲材料的空间中。蒙脱石晶体层对海水中阳离子的过滤能力被认为是这一机理。认为这种作用是通过膨润土的硬化来实现的。虽然在本实验条件下适用性有限，但在本实验结果的基础上，将经验方程建立为“Komine and Ogata评价膨胀特性方程”，得到了海水条件下较好的自密封性能方程。综合上述结果，从海水条件下自密封性能的角度构建了设计方法。少

Disposal of high-level radioactive wastes exhausted from nuclear power plants is an important problem that should be solved in the 21st century. In this plan, there is a material that is called"Bentonite based buffer material"in one of the multiple barriers. Bentonite based buffer material fills up a space between waste container and surrounding bedrock Moreover, a disposal facility has the possibility that is constructed in the vicinity of the coastal zone by the convenience of the wastes form transportation.To contribute this project, this study aimed to evaluate the self sealing behavior of bentonite based buffer material in the seawater condition quantitatively, and to establish design method of bentonite based buffer material from a viewpoint of self-sealing property under seawater condition.In this study,"self-sealing test by the one-dimensional model"was done in the beginning, and the self-sealing behavior in the seawater condition was investigated. This experiment is one-dimens … More ional model test to imitate the self-sealing behavior of seawater condition by installing a space that scales down the relation between the space part of an actual disposal site and the buffer material in the one dimension, and supplying artificial seawater of a different concentration.Next, the factor thought to be influence on the self sealing behavior was investigated Concretely, the invasion situation of the seawater element in the pore water of the specimen was investigated by measuring each cation exchange capacity (EXC) and exchangeable cation (CEC) of Na^+, Ca^<2+>, K^+, and Mg^<2+> ions in the specimen after it experimented.In addition, the equation that was appreciable of self-sealing behavior under seawater condition was made by building the empirical equation based on the result of this experiment into the self-sealing behavior of the buffer material in the distilled water condition to forecast and appreciable"equations for evaluating the swelling behavior".The new finding obtained for this research is shown below.1.In the following conditions, it has been understood that influence of seawater on self-sealing behavior is small from this self sealing test. In the bentonite A, if the space is 1.25mm or less and concentration of supplied solution is 100% or less of sea concentration, it has been understood that influence of seawater is small. And in the bentonite B and E, if the space is 1.25mm or less and concentration of supplied solution is 10% or less of sea concentration, it has been understood that influence of seawater is small.2.It was shown that there was a possibility because of seawater was not infiltrated in the space of the buffer material as one of the reasons for the decrease in self-sealing behavior is small under the seawater condition. The filter ability of cation in seawater by montmorillonite crystalline layer is thought as this mechanism. And it is thought that this function works effectively by hardening the bentonite well-set.3.Though the applicability was limited in this experiment condition, the equation that was appreciable of self sealing behavior under seawater condition was made by building the empirical equation based on the result of this experiment into"equations for evaluating the swelling behavior by Komine and Ogata".4.Synthesizing the above-mentioned result, design method was constructed from viewpoint of self sealing property under seawater condition. Less