Geological disposal of high-level radioactive waste and the role of rock engineering

高レベル放射性廃棄物の地層処分と岩石工学の役割

杉原 弘造

Sugihara, Kozo

原子力機構とその前身は、高レベル放射性廃棄物の地層処分の科学的,技術的基盤を整備するために、日本において1970年代から、深地層の科学的研究を行ってきた。この研究の一部として、堆積軟岩については東濃鉱山で、結晶質岩については釜石鉱山で、原位置試験を行った。この中で行った掘削影響試験では、掘削影響領域の広がりや特性,計測手法の有効性を評価した。機械掘削や制御発破により、坑道周辺岩盤への影響を低減できたが、詳細な掘削影響の評価のためには、計測・解析手法の改良が必要であることがわかった。原子力機構は、現在、超深地層研究所計画と幌延深地層研究計画という二つの深地層の研究施設計画を進めている。大深度での破壊現象,広域応力場,長期力学安定性の評価が、これらの計画における岩盤力学研究の課題である。これらの計画では、国際協力の推進を目指している。

JAEA and its predecessors have been conducting an extensive geoscientific research program since the 1970's in order to contribute to the formation of a firm scientific and technological basis for the geological disposal of high level radioactive waste in Japan. As a part of this program, in situ experiments have been performed at the Tono Mine in soft sedimentary rocks and at the Kamaishi Mine in hard crystalline rocks. An experiment on excavation disturbance has been one of these experiments and has revealed the extent and properties of the EDZ and the applicability of available measurement methods. It is suggested that mechanical excavation and controlled excavation have reduced excavation damage of the rock mass around a drift, although some improvements in the currently available methods for measuring and simulating the EDZ are essential to understand excavation disturbance in more detail. JAEA is now promoting two underground research laboratory projects in Japan; the Mizunami Underground Research Laboratory project for crystalline rocks and the Horonobe Underground Research Laboratory project for sedimentary rocks. From a rock mechanical point of view, the major interest in these projects will be paid to failure phenomenon in deep underground, rock stress estimation at larger scales and long-term physical stability of underground structure. These projects are open for international collaboration.