報告書番号

U03058

タイトル（和文）

熱・水を考慮したHLW処分施設の長期安定性に関する数値解析的検討 --岩盤・緩衝材の長期変形，熱・水の輸送に対する個別解析--

タイトル（英文）

Numerical analysis for long-term stability of HLW disposal facility considering thermal and hydraulic effect -Uncoupled analysis for long-term deformation of rock and buffer material and for transport of heat and water-

概要 （図表や脚注は「報告書全文」に掲載しております）

高レベル放射性廃棄物処分においては地下深部特有の高圧・地下水流動場という複合的環境下での地下処分施設の長期安定性を評価することが重要となる．この問題に対しては熱・水・応力連成解析を適用することが国際的に検討されているが，現状の整理を行ったところ，力学モデルに関して更なる高度化が必要と考えられる．また，処分場全体での連成解析に先立ち，既往の検討を基本として４つの個別現象（岩盤・緩衝材の長期力学挙動、水・熱の輸送）に対して感度解析を実施し，連成解析モデル開発の際、重要となる項目の抽出を行った．この解析により力学挙動においては緩衝材の膨潤特性，再冠水時間に対しては天然バリアの透水特性，温度分布に対しては緩衝材の飽和による熱物性の変化および間隙の充填が特に重要であることが明らかとなった．以上の現状分析・個別解析で得られた知見に基づき，連成解析プログラム開発を進める．

概要 （英文）

For the early realization of HLW geological repository and for its rational and economical design and safety assessment, it is important to evaluate the stability of repository facilities in deep underground, where high temperature, earth pressure and underground water flow affect the stability. This report discusses the numerical approaches that are useful for attaining these objectives. One of the efficient approaches is to develop models capable of simulating coupled thermo-hydro-mechanical (T-H-M) processes. Several T-H-M coupled simulation codes have been proposed and the international cooperative research project DECOVALEX has been held from 1991 in order to develop and validate the T-H-M coupled simulations. But mechanical models adopted in these simulation codes are too simple to be applied to the evaluation of long-term interaction of materials that show nonlinear mechanical behavior (especially in the case that surrounding rock is soft sedimentary rock). Before simulating the long-term and coupled phenomena, uncoupled simulations for four phenomena (creep behavior of surrounding rock mass, consolidation and deformation behavior of buffer material, transport of water, and transport of heat) are conducted using various parameters and boundary condition sets. From the results of those simulations, following conclusions are obtained: (1) swelling property of buffer material is important to evaluate mechanical behavior of barrier materials, (2) hydraulic properties of natural barrier can be more important than that of buffer material because suction effect of buffer material is so strong that transport of water in the buffer material is fast, (3) change of thermal properties and filling of gaps caused by water saturation of buffer material have a strong effect on the temperature field. On the next stage, we will develop a T-H-M coupled simulation code to evaluate the mechanical interaction between barrier materials based on the above study.

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