報告書番号

N11021

タイトル（和文）

イオン交換水で飽和したベントナイト系材料の透水性と膨潤特性に及ぼす熱影響に関する実験的検討

タイトル（英文）

Experimental study of thermal effect on permeability and swelling property of compacted bentonite saturated with deionized 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施設で使用が検討されているベントナイト系材料は、廃棄体の発熱により長期間高温環境下にさらされる可能性がある。そのため、本研究では飽和したベントナイト系材料（乾燥密度1.5Mg/m3）の高温環境下（60、90、120℃）での膨潤圧および高温履歴を付与した後の透水係数と平衡膨潤圧を実験的に評価した。高温履歴を付与した供試体の透水係数はいずれのケースでも加熱前と同程度の値であり、透水係数への高温履歴の影響は小さかった。加熱期間中の膨潤圧は室温で測定される値よりも小さい値であり、加熱温度が高いほど膨潤圧の低下率は大きかった。また、加熱前後の供試体の室温で測定された平衡膨潤圧は、60℃と90℃では同程度の値を示し、高温履歴の影響は小さかった。一方，120℃で加熱した供試体では，平衡膨潤圧が加熱前よりもわずかに低下した． （371文字）

概要 （英文）

Bentonite as an engineered barrier for high level radioactive waste disposal (HLW) facility would be exposed under high-temperature conditions, that arise from the decay heat released from the high level radioactive waste, for a long period of time. Therefore, the effect of high-temperature conditions and thermal history on the performance of bentonite material should be investigated for the safety assessment of HLW. In this study, the saturated compacted bentonites of the dry density of 1.5 Mg/m3 were used in heat experiments (60, 90 and 120 C). Swelling pressures of the saturated compacted bentonites were investigated under 60, 90 and 120 C conditions. Furthermore, the permeability and the equilibrium swelling pressure of the saturated compacted bentonites experienced thermal history were also measured at room temperature.
The dry densities and effective montmorillonite densities of saturated compacted bentonites after heat experiments at 60 and 90 C were comparable as that before heating. On the other hand, the dry density of saturated compacted bentonites after heat experiments at 120 C was slightly decreased. No changes of mineralogical feature of bentonite (i.e. mineral compositions, cation exchange capacity and montmorillonite content) and of montmorillonite (i.e. illitization, baideritization and increasing of layer charge) were observed in all case of heat experiments. Since the permeability of each saturated compacted bentonite after heat experiments were similar to that before heating, the effect of thermal history on the permeability was small. The swelling pressures of the saturated compacted bentonites under high-temperature conditions were smaller than that measured at room temperature. The decreasing rate of swelling pressure was increased with the increasing of the temperature. The equilibrium swelling pressure of the saturated compacted bentonites after heat experiments at 60 and 90 C were comparable as that before heating. Therefore, the effect of thermal history on the equilibrium swelling pressure was small below 90 C. On the other hand, the equilibrium swelling pressure of the saturated compacted bentonites after heat experiments at 120 C was slightly smaller than that before heating. This decrease of the equilibrium swelling pressure would be due to the decrease of the dry density and/or the effect of the silica cementation.

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