報告書番号

U02047

タイトル（和文）

深部地下構造物に対する化学作用およびその数値モデル化に関する調査

タイトル（英文）

Review on chemical processes around the facilities in deep underground and study on numerical approach to evaluate them

概要 （図表や脚注は「報告書全文」に掲載しております）

放射性廃棄物処分場は地下深部に建設されるが、微生物を含む種々の化学的作用が人工・天然バリア機能に長期的に影響を与える可能性があり、バリア材料の長期挙動に対する評価手法の高度化が望まれる。長期挙動評価の有力手法の一つは、化学作用をモデル化し、シミュレーション計算によって評価を行う方法である。 地下深部の構造物に作用する化学的作用および微生物作用について整理し、その化学プロセスに対する数値シミュレーションによる評価の現状についてまとめた。発生する化学反応の大部分は地下水と鉱物の反応であり、化学反応-物質移行連性モデルにより、化学反応の進行による水質変化・組成変化が評価可能である。さらに、それらと材料物性の関係のモデル化ができれば、長期的な材料変性の評価が可能である。

概要 （英文）

The facilities for radioactive waste repositories are constructed in deep underground. Various chemical reactions including microbial activities may affect the long-term performance of the barrier system. An advancement of the evaluation method for the long-term behavior of barrier materials is desired. One of the efficient approaches is numerical simulation based on modeling of chemical processes. In the first part of this report, chemical processes and microbial reactions that can affect the performance of facilities in deep underground are reviewed. For example, dissolution and precipitation of minerals composing bentonite and rock are caused by highly alkaline water from cementitious materials. Numerical approaches to the chemical processes are also studied. Most chemical processes are reactions between groundwater (or solutes in it) and minerals composing barrier materials. So they can be simulated by coupled reaction rate transport analyses. Some analysis codes are developed and applied to problems in radioactive waste disposal. Microbial reaction rate can be modeled using the growth equation of microorganisms. In order to evaluate the performance of the barrier system after altered by chemical processes, not only the change in composition but also properties of altered materials is required to be obtained as output of numerical simulation. If the relationships between reaction rate and material properties are obtained, time history and spatial distribution of material properties can also be obtained by the coupled reaction rate transport analysis. At present, modeling study on the relationships between them is not sufficient, and obtaining such relationships using both theoretical and experimental approaches is also an important research target.

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