Development of evaluation for swelling and sealing characteristics of heated bentonite based buffer in high-temperature conditions.

核电站排出的高放废物具有很高的放射性水平，需要很长的时间才能对人类的生存环境产生影响。因此，高活性废物的长期安全储存和管理是非常困难的。在国际上，地质处理被认为是最好的。同样在日本的高活性废物储存约30-50年，并计划将其处置到地下300米以下的地质层。认为在地质处理时，采用工程屏障和天然屏障组成的复合屏障系统，可以长期安全地隔离高活性废物。工程屏障由玻璃化废物、外包装和缓冲材料组成。膨润土具有自封性，可作为缓冲材料使用，具有广阔的应用前景。另一方面，TH…更多的高放射性废物通过放射性的衰变释放出大量的放射性衰变热。缓冲材料的内部由于放射性衰变热而变得高温。将地下高活性废物处理后，缓冲材料内的温度达到几十年来的最高水平。随着时间的推移，它逐渐减少。然而，这种高温状态预计至少会持续数百年。膨润土基缓冲材料具有良好的自封性，但膨胀前的放射性衰变热会降低材料的自封性，为解决上述问题，本研究通过实验研究了部分热历史对膨润土材料自封性的影响。本研究采用A、B、C、E四种膨润土，加热温度分别为60℃、90℃、110℃、130℃。本研究进行了膨胀压力实验和膨胀变形实验。结果表明，膨润土A、B、E的热历史对膨化压力特性的影响较小。此外，在围压为1000kPa时，热历史对膨胀变形性能的影响较小。膨润土C的热历史对其在炼焦应力1000kPa时的膨胀变形性能影响不大。在初始干密度较高的条件下，膨润土C的热历史对膨化压力特性的影响较小。此外，在加热温度为60℃时，热历史对膨润土的膨胀变形性能影响不大。为探讨热历史对膨润土膨胀特性的影响机理，本研究进行了X射线衍射分析、实验后的水化学分析、实验前后的亚甲基蓝吸附实验和阳离子交换容量测试。综合以上实验结果，认为膨润土A的溶胀特性的降低是由于蒙脱石对阳离子的吸附能力降低。认为膨润土C的溶胀性能的降低是由于蒙脱石含量的减少。在以上实验结果和机理探讨的基础上，本研究提出了“考虑热历史影响的溶胀行为评价方程”。在提出的方程中，认为蒙脱石的阳离子吸附能力随热历史的变化而降低。根据亚甲基蓝吸附量的测定结果，计算了阳离子交换量和阳离子交换量。将上述方程的计算结果与实验结果进行了比较。通过计算结果，验证了所提出的方程的正确性。较少

High-level radioactive waste (HLW) exhausted from the nuclear plant has very high radioactivity level, so it will be required the very long term of years to become no influence to human's living environment. Therefore, it is very difficult to keep storing and to manage high activity waste for a long term safely. In the international society, it is considered that the geological disposal is the best. The high activity waste also in Japan is stored for about 30-50 years, and it is scheduled to dispose to geologic layer deeper than 300m in the underground. It is thought that the high activity waste can be safely isolated for a long term by adopting the multibarrier system that consists of the engineered barrier and the natural barrier when geological disposal. The engineered barrier is composed of the vitrified waste, overpack, and buffer material. The use of the bentonite that has the self sealing by the swelling for the material of the buffer material is promising. On the other hand, th … More e high activity waste evolves a large amount of radioactive decay heat by decay of the radioactivity. The inside of the buffer material becomes a high temperature by the radioactive decay heat. The temperature in the buffer material becomes the highest in tens of years after disposing the high activity waster in underground. It decreases gradually with the passage of time. However, the state of the high temperature has expected to continue for at least many hundreds of year. The-self-sealing expected of a bentonite-based buffer material is demonstrated by swelling However, the decrease in the self-sealing is afraid by the radioactive decay heat before the swelling.To solve the problem mentioned above, this study investigated the influence of some thermal histories to swelling of bentonite materials by experimental works. This study used four kinds of bentonite named A, B, C, and E. The thermal temperatures were 60, and 90, 110, 130℃. This study conducted the swelling pressure experiment and the swelling deformation experiment. From the results, the influence of the thermal history of bentonite A, B, and E, was a little in the swelling pressure characteristics. In addition, the influence of the thermal history was a little in the swelling deformation property in case of confining stress 1000kPa. The influence of the thermal history of bentonite C was a little in the swelling deformation property in case of cofining stress 1000kPa. The influence of the thermal history of bentonite C was a little in the swelling pressure characteristics of condition with a high initial dry density. Moreover, the influence of the thermal history was a little in the swelling deformation property in case of cofining stress 1000kPa of the heating temperature 60℃.To discuss the mechanism on influences of thermal history to swelling characteristics of the bentonite, this study conducted the X-ray diffraction analysis, surround water chemical analysis after experiment, and the methylene blue absorption tests and the cation exchange capacity of bentonite before and after experiments. From the above experimental results, the decrease in the swelling characteristics of bentonite A was considered as the decrease in the adsorption ability of the cation of montmorillonite. The decrease in the swelling characteristics of bentonite C was considered as the decrease of content of montmorillonite. Furthermore, this study proposed "Equations for evaluating the swelling behavior that considered the influence of the thermal history" on the basis of the above experimental results and discussions of mechanism. In this proposed equations, it was considered that the cation adsorption ability of montmorillonite decreased by the thermal history. The exchangeable cation amount and the cation exchange capacity were calculated based on the measurement result of the amount of the methylene blue adsorption. The calculated results by the above proposed equations were compared with the experimental results. From the results, the validity of proposed equations was clarified. Less