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The Japanese approach to developing clay-based repository concepts; An Example of design studies for the assessment of sealing strategies

粘土系材料を基本とした処分概念に関する日本のアプローチと閉鎖性能評価にかかわる設計研究

杉田 裕; 藤田 朝雄; 高橋 義昭*; 川上 進; 梅木 博之; 油井 三和; 浦上 学*; 北山 一美*

Sugita, Yutaka; Fujita, Tomoo; Takahashi, Yoshiaki*; Kawakami, Susumu; Umeki, Hiroyuki; Yui, Mikazu; Uragami, Manabu*; Kitayama, Kazumi*

本論文はPhysics and Chemistry of the Earth Tours 2005 Meeting特集号に投稿する論文である。日本の処分事業を進めるうえでのアプローチについて紹介するとともに、処分場概念の設計へ反映する材料の要件の検討の一例として、処分場の閉鎖にかかわる材料と人工バリア材料との関連について水理解析の結果を示している。処分事業を進めるうえでのアプローチとしては、公募方式の採用に基づき、処分場が決まっていない前提条件でどのように処分場の性能を確保するか、その確からしさが段階を追って精度を増すという考え方を示したものである。

The H12 repository concept for vitrified high-level radioactive waste was developed based on a multi-barrier system with the emphasis on robust engineered barrier performance to ensure its feasibility for a wide range of geological conditions typically observed in Japan. The buffer is clay-based and plays a very important role in the engineered barrier system (EBS). The decision to use a volunteer siting process requires maximum flexibility of the repository concept to allow it to be adapted to potential sites and hence a wide range of variants of the basic H12 repository design has been developed. In order to evaluate the feasibility and the applicability of different repository options to specific siting environments, NUMO has established a set of "design factors" which classify the aspects that need to be considered when evaluating the pros and cons of different repository options. A Na-type bentonite from Japan is used as the reference material for all clay-based repository components (buffer, backfill, clay plug, etc.). The characteristics of this bentonite (thermal, mechanical, chemical, hydraulic) have been examined with consideration of various practical constraints (limitation on the repository footprint, the influence of saline water, the interaction of hyperalkaline leachates and practical working environment, etc.). Clay-based seals, which close off the tunnels after emplacement of the EBS, may also be key components for assessment of the repository. Full analyses considering all engineered barrier components (buffer, backfill, clay plug, concrete lining, tunnel, concrete plug, host rock) that may be used in a repository will be an essential future task. As a first step towards this goal, a numerical analysis focusing on hydraulic behaviour at the intersections of the disposal tunnels and the main tunnel is presented to illustrate how the design requirements of clay-based seals can be determined.

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パーセンタイル:83.8

分野:Geosciences, Multidisciplinary

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