Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
笹本 広; Arthur, R. C.*
Environmental Earth Sciences, 85(13), p.300_1 - 300_16, 2026/07
被引用回数：0Fractured rocks in the Excavation Damage Zone (EDZ) and intact host rocks of a geologic repository for radioactive waste could be altered by reactions with hyperalkaline solutions leached from cementitious materials in the repository. Alteration could cause individual fractures to open (i.e., propagate) or close (i.e., seal) under the control of coupled fluid-flow, solute-transport, and water-rock interaction processes. A discrete-fracture, reactive-transport model was used in the present study to evaluate fracture propagation/sealing behavior caused by reactions involving hyperalkaline solutions with minerals in a representative repository host rock. Differences in assumptions underpinning the model were found to strongly affect system behavior. Model results indicated the rock matrix adjacent to a fracture would seal relatively quickly, for example, if a constant-concentration condition was assumed along the fracture-matrix boundary. Conversely, the model predicted that the matrix would not seal completely near the fracture surface if a constant-concentration boundary was assumed at the inlet rather than along the fracture-matrix interface. Fracture flow would slow by precipitation of secondary minerals in this latter case, however, causing the fracture porosity and permeability to decrease. Sensitivity analyses based on a critical evaluation of initial and boundary conditions in discrete-fracture models can provide important insights concerning phenomena controlling fracture propagation/sealing behavior and related impacts on fluid flow and radionuclide transport.
田窪 勇作*; 高山 裕介*; 杉田 裕; 生越 季理; 石田 圭輔*
Environmental Earth Sciences, 85(9), p.229_1 - 229_19, 2026/05
被引用回数：0 パーセンタイル：0.00(Environmental Sciences)In this study, sensitivity analysis was conducted to identify key parameters that strongly influence infiltration assessment. The results indicate that the intrinsic permeability and the water retention function have a significant impact on the simulation of liquid saturation as key parameters to be focused on the hydraulic modelling. Furthermore, the results of hydraulic analysis for saltwater infiltration with various concentrations suggest that the hydraulic analysis model is applicable for evaluating infiltration behaviour, by setting several analysis cases focused on variabilities of key parameters. This modeling approach, which focuses on the key parameters, has the potential to be a simple method to predict the hydraulic state transition of the buffer material during re-saturation period.
佐久間 圭佑; 石井 英一; 村上 裕晃
Environmental Earth Sciences, 84(22), p.663_1 - 663_11, 2025/11
被引用回数：0 パーセンタイル：0.00(Environmental Sciences)The safe geological disposal of high-level radioactive waste requires consideration of the inflow of groundwater from faults or fractures encountered during excavation of deep underground tunnels, as this inflow may adversely affect the installation and performance of bentonite buffers. The water pressure diffusion equation, assuming uniform hydraulic conductivity and specific storage, predicts that the inflow rate from faults or fractures naturally decays at a rate depending on the flow dimension when the cross-sectional area of the flow areas in the fault or fracture system is proportional to the power of the distance from the inflow point. Although this prediction has been verified for decay ratios measured a few weeks after tunnel excavation, its applicability to long-term predictions several years after excavation has not yet been assessed. We investigated the natural inflow decay ratios (i.e., the inverse of the current inflow rate normalized to the initial inflow rate at excavation) at fault-related inflow points in a tunnel at 350 m depth in the Horonobe Underground Research Laboratory, Japan, 10 years after tunnel excavation, and compared them with those modelled using the diffusion equation and flow dimension. The natural inflow decay ratio measured at each inflow point was equal to or higher than the modelled ratio. Although in some cases the measured ratios may be up to four times as high as the maximum modelled ratio, this difference can be explained by the effect of hydraulic interference between adjacent inflow points. The diffusion equation and flow dimension can be used to predict the minimum long-term (several years or longer) natural decay ratio, providing useful insight to implications for repository design timelines or regulatory decisions (e.g., determining when and where to install waste and bentonite buffers in a repository).
青柳 和平; 石井 英一
Environmental Earth Sciences, 83(3), p.98_1 - 98_15, 2024/02
被引用回数：3 パーセンタイル：33.58(Environmental Sciences)高レベル放射性廃棄物の地層処分において、坑道掘削損傷領域の透水性の経時変化の予測が、掘削損傷領域内部の割れ目を介した放射性核種の移行特性の評価の信頼性向上において重要となる。特に人工バリア定置後の緩衝材の膨潤圧発生に伴う割れ目の透水性の変化を検討することを目的として、幌延深地層研究センターにおいて実施している実規模の人工バリア性能確認試験領域付近で4年間透水試験を実施した。試験の結果、透水性は時間とともに低下し、膨潤から4年経過した時点で、試験開始時よりも透水性が41%に低下することが確認された。さらに、Barton-Bandisのモデルを適用することにより、膨潤圧の変化に伴う透水性の低下挙動を定量的に再現することができた。割れ目の閉塞の妥当性については、人工バリア性能確認試験実施領域で実施した弾性波トモグラフィ調査において、特に底盤部分の弾性波速度の増大が見られたことから確認することができた。これらの結果から、人工バリアの膨潤に伴う掘削損傷割れ目の閉塞について、実証することができた。また、地層処分事業において、廃棄体定置後の緩衝材の膨潤による掘削損傷割れ目の透水性の事前予測に際してBarton-Bandisモデルの適用可能性が示された。
岩月 輝希; 萩原 大樹; 大森 一秋; 宗本 隆志; 尾上 博則
Environmental Earth Sciences, 74(4), p.3041 - 3057, 2015/08
被引用回数：20 パーセンタイル：55.50(Environmental Sciences)岐阜県瑞浪市の超深地層研究所において、深度500mまでの坑道掘削及び維持管理時の地下水の水理・化学変化の観測を行った。その結果、水位低下や深部地下水の湧昇に伴う地下水の水質変化とそのプロセスを把握することができた。また、観測結果から大規模地下施設を結晶質岩に建設する時の留意点を整理することができた。
