Hideo Komine

Simplified evaluation for swelling characteristics of bentonites

Bentonite is currently planned to be used as buffer and backfill materials for repositories of high-level nuclear waste because these materials must have the swelling characteristics to seal the waste. In the design for buffer and backfill materials, we must choose the adequate bentonite among many kinds of bentonite in the world. The database of the swelling characteristics of various bentonites and its evaluation will be available when we will select the adequate bentonite. For this purpose, this study performed the laboratory tests on the swelling pressure and swelling deformation of four kinds of bentonite produced in Japan and the United States. These bentonites have different physicochemical properties. This study investigated the characteristics of swelling pressure and swelling deformation from the viewpoint of the physicochemical properties of each bentonite. Furthermore, this study also proposed the simplified evaluation of swelling characteristics of various bentonites on the basis of microscopic analysis.

Swelling characteristics of bentonites in artificial seawater

Bentonite is currently designated for use as a buffer material for the repository of high-level radioactive waste because such a material requires swelling characteristics to seal the waste. A high-level radioactive waste disposal facility may be built in a coastal area of Japan because transportation of this waste by ships is feasible. Therefore, it is important to investigate the effects of seawater on a bentonite-based buffer. This study is intended to investigate the influence of seawater on the swelling pressure and swelling deformation characteristics of five common types of bentonite. The experiments described herein clarify the relations between the influence of seawater grade and compaction density, type of exchangeable cation, montmorillonite content of the bentonite, and vertical pressure condition. Based on experimental results, suitable specifications have been defined for a bentonite-based buffer that can withstand the effects of seawater.

Radiation-Shielding Properties of Heavy Bentonite-Based Slurry for the Decommissioning of the Fukushima First Nuclear Power Plant

Abstract: The 2011 off the Pacific coast of Tohoku earthquake has impacted Japan, and it made serious damage to nuclear power plant in Fukushima. At present, Japanese government and engineers proceed decommissioning of the power plant, and ensuring safety of workers is the most important matter especially in fuel debris retrieval. On these backgrounds, the authors focus on heavy bentonite based slurry for filling material of nuclear reactor. Heavy slurry is capable of shielding gamma ray and neutron beam from its high specific gravity and water content. The purpose of this research is to investigate and define the properties of heavy bentonite based slurry by soil mechanics experiment. That is, the research described in this paper is a proposal to use it for decommissioning of the Fukushima I nuclear power plant. For quantifying the radiation shielding properties, the authors measured the transmitted radiation dose through heavy slurry. The result shows the heavy slurry has definite radiation shielding properties. In conclusion, the heavy bentonite based slurry may be useful for radiation shielding, and save workers health in particular.

EXPERIMENTAL STUDY ON MANUFACTURE OF BLOCK-TYPE BUFFER FOR HIGH-LEVEL RADIOACTIVE WASTE DISPOSAL

高レベル放射性廃棄物の地層処分において, ベントナイトは低透水性と高い膨潤性等の特性を有することから緩衝材としての利用が有望視されている. 緩衝材は地上に建設された工場において, 乾燥密度が1.6～2.0Mg/m3程度のブロック状に製作されたものを廃棄物収納容器と周辺岩盤の間に設置する方法が有力と考えられている. 緩衝材の製作方法の一つとして, 金型モールドを用いて静的な圧力をかけて締固めるという方法が検討されているが, 実際に緩衝材を製作するにあたっては, 解決すべき様々な問題があると予想されている. 本研究では, ベントナイトおよびベントナイトと砂の混合材料を用いて, 縮尺模型のブロック型緩衝材の製作実験を行い, 緩衝材製作上の問題点とその解決のための対策を提案した.