報告書番号

T02003

タイトル（和文）

TRU廃棄物処分環境におけるセメント系材料の化学的変質評価（その３） --カルシウムシリケート水和物の非調和溶解モデルを考慮した化学平衡-物質輸送連成計算コードの開発--

タイトル（英文）

Chemical Alteration of Cement Materials in a Radioactive Waste Repository Environment (3)-Development of Reactive Transport Computational Code Combined with Incongruent Dissolution Model of Calcium Silicate Hydrates-

概要 （図表や脚注は「報告書全文」に掲載しております）

セメント系材料で構築されたTRU廃棄物の地下処分施設の長期的な変質挙動の評価のため、セメント水和物を含んだ体系に適した地球化学モデルと物質輸送モデルをカップリングした計算解析コードが開発された。当所で提案したC-S-Hゲルの非調和溶解モデルを、公開の地球化学計算コードHarphrqに組み込んだ。さらに、簡略化された物質輸送モデルであるコンパートメント間の移行モデルとのカップリングを行なった。このカップリングコードは、普通ポルトランドセメントの溶解試験やカラム型変質試験ので得られた平衡水組成の変化や鉱物組成の変化を定量的に予測できることが示され、コードの妥当性が検証された。また、この試験結果の解析評価から、C-S-HゲルのCa/Si比の分布や、再沈殿の挙動など、既存のカップリング計算モデルでは得ることの出来ない、特徴のある有益な評価結果が得られた。

概要 （英文）

For long-term performance assessment of a cementitious disposal system for TRU waste, a so-called reactive transport computational code, being a numerical simulation code coupled a geochemical model suited to the system includes cement hydrate and a solute transport model, so-called reactive transport computational code, has been developed. The thermodynamic model previously developed in our institute for incongruent dissolution of calcium silicate hydrate (C-S-H) gel, which is a principal product of hydrated cement phase, was incorporated into a geochemical code, Harphrq, to evaluate chemical equilibrium conditions containing cement hydrates. This modification of the code enables a user to evaluate adequately the chemical equilibrium of a system including cement hydrate, such as a dissolution/precipitation of C-S-H gel and/or a change of Ca/Si ratio in C-S-H gel. The modified geochemical code was coupled onto a simplified solute transport code using a compartment model. The coupled code could simulate the processes where various chemical species in aqueous phase migrate through the homogeneous porous materials while locally maintaining chemical equilibrium.The developed reactive transport computational code was verified by comparison with experimental results on batch-type dissolution tests and column-type alteration tests under flow-through conditions of ordinary Portland cement hydrate. Predictive calculation results by the developed code were reasonably accordant with the experimental results, e.g. the distribution of constituent minerals and the composition of pore water in altered ordinary Portland cement hydrate. The validity of the developed code was therefore verified. Analysis on the results by the calculation could indicates special features such as a distribution of Ca/Si ratio in C-S-H gel along the water-flow in the column, and a re-precipitation of C-S-H gel in the downstream side of the dissolution front of C-S-H gel.

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