報告書番号

N14003

タイトル（和文）

遠心力載荷装置を用いた高レベル放射性廃棄物処分場周辺の長期挙動評価（その４）－加熱型廃棄体を用いた等方応力拘束条件下における熱－水－応力連成模型実験－

タイトル（英文）

Simulation of long-term behavior in HLW near-field by centrifugal model test (Part 4) -Model test of coupled THM processes in isotropic stress conditions using heatable overpack-

概要 （図表や脚注は「報告書全文」に掲載しております）

本研究では高レベル放射性廃棄物地層処分場周辺（ニアフィールド）の長期挙動評価のために，遠心力載荷装置を用い，廃棄体の発熱を考慮したニアフィールド模型試験を行った．縮小模型は岩盤(軟岩)，緩衝材，加熱型廃棄体から成り，地圧相当の応力を負荷し30Gの遠心場において最長80日間実施された．その結果，計測値の経時変化は，実験初期においては常温実験の結果と類似した傾向が見られた．一方で，数百時間の通水後，廃棄体の変位が沈下から浮上に転じるなど，相違もあった。また，実験終了後のX線CT撮影から廃棄体周辺の緩衝材の密度が常温実験より低く，想定飽和密度に達しておらず，加えて，数百時間経過後に間隙注水流量に変化が生じていた．すなわち，高温の廃棄体が緩衝材の間隙水分布に影響を与え緩衝材の密度が低下，これにより緩衝材の土圧と処分孔の剛性が低下し，これが周辺岩盤のひずみと廃棄体の変位傾向に影響した可能性がある．

概要 （英文）

We demonstrated the equivalent long-term behavior in the near-field of a geological repository for high level radioactive waste disposal, using the centrifugal near-field model test under the coupled thermo-hydraulic-mechanical condition. The model consisted of a sedimentary bedrock, buffer, and heating type model overpack, and was enclosed within a pressure vessel. Tests were conducted with a centrifugal force field of 30 G under isotropic stress-constrain conditions with confining pressures and injection of pore water. The temperature condition of the overpack was constantly 95 decree-C. As the result, the values showed similar behaviors to that of the normal temperature tests partially. However, the different behaviors were measured such as the displacement of overpack change from the settlement to the heave, the extreme drop in the soil pressure of the buffer and the strain of side wall of bedrock change from the tension to the compression after injecting pore water of hundreds hours. In addition, the flow rate of the injection pore water suddenly changed after hundreds of hours. Furthermore, the density of the buffer was lower than that of the normal temperature tests by X-ray CT imaging in the post-tests. We infer that the high temperature overpack influenced the stiffness and the pore water distribution of the buffer, and the density and the soil pressure of the buffer decreased. As a result of the change of stiffness in the disposal hole (buffer), the tendency to the strain of the surrounding bedrock and the displacement of the overpack changed.

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