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

核电站高放废物的处置是21世纪世纪必须解决的重要问题。在该计划中，在多个屏障中的一个屏障中有一种被称为“膨润土基缓冲材料“的材料。膨润土基缓冲材料填充了废物容器与周围基岩之间的空间。此外，由于废物运输的便利，处置设施有可能建在海岸带附近。为了促进该项目，本研究旨在定量评估膨润土基缓冲材料在海水条件下的自密封行为。从海水条件下自密封性能的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“，考察了膨润土基缓冲材料在海水条件下的自密封性能。这个实验是一维的 ...更多信息 通过设置在一维上缩小实际处置场的空间部分与缓冲材料之间的关系的空间，并供给不同浓度的人工海水，模拟海水条件下的自密封行为的离子模型试验。其次，对被认为影响自密封行为的因素进行了具体研究。通过测定实验后样品中Na^+、Ca^2+、K^+和Mg^2+离子的各阳离子交换量（EXC）和可交换阳离子（CEC），研究了海水元素在样品孔隙水中的侵入情况，另外，通过将基于本实验结果的经验方程建立到缓冲材料在蒸馏水条件下的自密封行为中，得到了在海水条件下的自密封行为的可感知方程，以预测和可感知的“膨胀行为评估方程”。从该自密封试验可以理解，海水对自密封性能的影响很小。在膨润土A中，如果该空间为1.25mm或更小并且供给溶液的浓度为海水浓度的100%或更小，则已经理解海水的影响小。并且在膨润土B和E中，如果空间为1.25 mm或更小并且供给溶液的浓度为海水浓度的10%或更小，海水的影响很小。2.缓冲材料的空间中没有渗入海水，这可能是自润滑性降低的原因之一。在海水条件下密封性小。认为蒙脱石晶层对海水中阳离子的过滤能力是其作用机理。3.虽然在本实验条件下适用性有限，但通过将基于本实验结果的经验方程建立为“Komine和Ogata评价膨胀行为的方程”，得到了在海水条件下具有明显自密封行为的方程。从海水条件下的自密封性能出发，提出了设计方法。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