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論文

Petrophysical properties of representative geological rocks encountered in carbon storage and utilization

Hu, Q.*; Wang, Q. M.*; Zhang, T.*; Zhao, C.*; Iltaf, K. H.*; Liu, S. Q.*; 深津 勇太

Energy Reports (Internet), 9, p.3661 - 3682, 2023/12

This study evaluates petrophysical properties of representative geological rocks in the context of injectivity, storage space, and caprock integrity for effective utilization and long-term storage of carbon dioxide. A total of 10 geological rocks were selected as representative storage media for consideration as saline aquifers & depleted oil and gas reservoirs, basalts, and cap rocks, as well as utilization in organic-rich shale and coal seams. An integrated suite of laboratory tests, including liquid immersion porosimetry, gas expansion porosimetry, grain size distribution, mercury intrusion porosimetry, and gas diffusion, were performed on these various rock samples. The results exhibit a disparity of petrophysical properties among two broad groups of rocks: rocks selected for possible storage of CO$$_{2}$$ have porosities of $$sim$$10-25%, permeabilities of $$sim$$10$$^{-16}$$-10$$^{-13}$$ m$$^{2}$$, $$mu$$m-sized pore-throat size distribution, and mostly good pore connectivity; in contrast, the potential caprocks have porosities of $$sim$$0.5-5%, permeabilities of $$sim$$10$$^{-20}$$-10$$^{-18}$$ m$$^{2}$$, pore throat sizes of $$<$$50 nm, and probably poorly connected pore networks. An understanding of the measured facets of pore structure and contribution of fractures is also critical in the context of different testing principles and data interpretation of petrophysical analyses, as well as observational scales in the laboratory and field, and therefore reliable confidence of CO$$_{2}$$ storage and utilization performance. Our work further illustrates the controlling influence of grain size distribution and geological processes on pore size distribution and pore connectivity for a wide range of rock types and lithologies, and particularly presents the extent and behavior of CO$$_{2}$$ gas diffusion with a custom-designed apparatus for a holistic understanding of various petrophysical attributes of widely different geological rocks.

論文

Predictive and inverse modeling of a radionuclide diffusion experiment in crystalline rock at ONKALO (Finland)

Soler, J. M.*; Kek$"a$l$"a$inen, P.*; Pulkkanen, V.-M.*; Moreno, L.*; Iraola, A.*; Trinchero, P.*; Hokr, M.*; $v{R}$$'i$ha, J.*; Havlov$'a$, V.*; Trpko$v{s}$ov$'a$, D.*; et al.

Nuclear Technology, 209(11), p.1765 - 1784, 2023/11

The REPRO-TDE test was performed at a depth of about 400 m in the ONKALO underground research facility in Finland. Synthetic groundwater containing radionuclide tracers (HTO, Cl-36, Na-22, Ba-133, Cs-134) was circulated for about four years in a packed-off interval of the injection borehole. Tracer activities were additionally monitored in two observation boreholes. The test was the subject of a modelling exercise by the SKB GWFTS Task Force. Eleven teams participated in the exercise, using different model concepts and approaches. Predictive model calculations were based on laboratory-based information concerning porosities, diffusion coefficients and sorption partition coefficients. After the experimental results were made available, the teams were able to revise their models to reproduce the observations. General conclusions from these back-analysis calculations include the need for reduced effective diffusion coefficients for Cl-36 compared to those applicable to HTO (anion exclusion), the need to implement weaker sorption for Na-22, compared to results from laboratory batch-sorption experiments, and the observation of large differences between the theoretical initial concentrations for the strongly-sorbing Ba-133 and Cs-134 and the first measured values a few hours after tracer injection. Different teams applied different concepts, concerning mainly the implementation of isotropic vs. anisotropic diffusion, or the possible existence of Borehole Disturbed Zones around the different boreholes. The role of microstructure was also addressed in two of the models.

論文

Pore connectivity influences mass transport in natural rocks; Pore structure, gas diffusion and batch sorption studies

Yuan, X.*; Hu, Q.*; Lin, X.*; Zhao, C.*; Wang, Q.*; 舘 幸男; 深津 勇太; 濱本 昌一郎*; Siitari-Kauppi, M.*; Li, X.*

Journal of Hydrology, 618, p.129172_1 - 129172_15, 2023/03

 被引用回数:0 パーセンタイル:0(Engineering, Civil)

Mass transport in geomedia as influenced by the pore structure is an important phenomenon. Six rocks (granodiorite, limestone, two chalks, mudstone, and dolostone) with different extents of heterogeneity at six different particle sizes were studied to describe the effects of pore connectivity on mass transport. The multiple methods applied were porosity measurement, gas diffusion test, and batch sorption test of multiple ions. Porosity measurement results reveal that with decreasing particle sizes, the effective porosities for the "heterogenous" group (granodiorite and limestone) increase, whereas the porosities of "homogeneous" group (chalks, mudstone, and dolostone) roughly remain constant. Gas diffusion results show that the intraparticle gas diffusion coefficient among these two groups, varying in the magnitude of 10$$^{-8}$$ to 10$$^{-6}$$ m$$^{2}$$/s. The batch sorption work displays a different affinity of these rocks for tracers, which are related to their mineral components. For granodiorite, mudstone, and dolostone, the adsorption capacity increases as the particle size decreases, due to higher specific surface area in smaller particle-size. In general, this integrated research of grain size distribution, rock porosity, intraparticle diffusivity, and ionic sorption capacity gives insights into the pore connectivity effect on both gas diffusion and chemical transport behaviors for different lithologies and/or different particle sizes.

論文

New approach to understanding the experimental $$^{133}$$Cs NMR chemical shift of clay minerals via machine learning and DFT-GIPAW calculations

大窪 貴洋*; 武井 滉洋*; 舘 幸男; 深津 勇太; 出口 健三*; 大木 忍*; 清水 禎*

Journal of Physical Chemistry A, 127(4), p.973 - 986, 2023/02

 被引用回数:0 パーセンタイル:0.01(Chemistry, Physical)

粘土鉱物へのCsの吸着サイトの特定は、環境化学の分野で研究されてきた。核磁気共鳴(NMR)実験によって、吸着されたCsの局所構造を直接観察することが可能である。固体NMR実験から得られた$$^{133}$$CsのNMRパラメータは、吸着されたCsの局所的な構造に敏感である。しかしながら、NMRデータだけからCsの吸着位置を決定することは困難であった。本研究では、機械学習と実験的に観察されたケミカルシフトを組み合わせることにより、粘土鉱物に吸着されたCsの吸着位置を特定するためのアプローチについて提示する。原子配置の記述子とNMRによるケミカルシフトの第一原理計算結果を関連付けて評価する機械学習の線形リッジ回帰モデルを構築した。これにより、原子配置の構造データから$$^{133}$$Csのケミカルシフトを高速で計算することが可能となった。機械学習モデルによって、実験的に観察された化学シフトから逆解析を行うことにより、Cs吸着位置を導き出すことが可能になる。

論文

Evaluation report of Task 9C based on comparisons and analyses of modelling results for the ONKALO REPRO-TDE experiment

Soler, J. M.*; Kek$"a$l$"a$inen, P.*; Pulkkanen, V.-M.*; Moreno, L.*; Iraola, A.*; Trinchero, P.*; Hokr, M.*; $v{R}$$'i$ha, J.*; Havlov$'a$, V.*; Trpko$v{s}$ov$'a$, D.*; et al.

SKB TR-21-09, 204 Pages, 2021/11

Task 9C of the SKB Task Force on Modelling of Groundwater Flow and Transport of Solutes (Task Force GWFTS) was the third subtask within Task 9 and focused on (1) predictive and (2) back-analysis modelling of experimental results from the REPRO-TDE in situ diffusion experiment. The test was performed at a depth of about 400 m in the ONKALO underground research facility in Finland. Synthetic groundwater containing radionuclide tracers (HTO, Cl-36, Na-22, Ba-133, Cs-134) was circulated for about four years in a packed-off interval of the so-called injection borehole. Tracer activities were additionally monitored in two observation boreholes arranged as a right-angled triangle and located at about 0.1 m wall-to-wall from the injection borehole. Eleven modelling teams participated in the modelling exercise, using different model concepts and approaches. Three main types of models were applied: (1) An analytical solution to the diffusion-retention equations, (2) continuum-porous-medium-type numerical models, and (3) microstructure-based models. The predictive model calculations were based on laboratory-based information concerning porosities, diffusion coefficients and sorption partition coefficients available in the task description. Microstructural characterisation of rock samples was also available and used by the teams using microstructure-based models.

論文

Diffusion of tritiated water, $$^{137}$$Cs$$^{+}$$, and $$^{125}$$I$$^{-}$$ in compacted Ca-montmorillonite; Experimental and modeling approaches

深津 勇太; 四辻 健治*; 大窪 貴洋*; 舘 幸男

Applied Clay Science, 211, p.106176_1 - 106176_10, 2021/09

 被引用回数:3 パーセンタイル:73.05(Chemistry, Physical)

Mechanistic understanding and predictive modeling of radionuclide diffusion in Na- and Ca-montmorillonite are essential to evaluate the long-term evolution of the bentonite barrier and their impact on radionuclide migration during geological disposal of radioactive wastes. Thus, the diffusion behavior of $$^{137}$$Cs$$^{+}$$, $$^{125}$$I$$^{-}$$, and tritiated water (HTO) in compacted Ca-montmorillonite was investigated as a function of porewater salinity and dry density via both experiments and models. The effective diffusion coefficient (De) followed in the order of $$^{137}$$Cs$$^{+}$$ $$>$$ HTO $$>$$ $$^{125}$$I$$^{-}$$. The De of $$^{137}$$Cs$$^{+}$$ decreased with increasing salinity, whereas the dependence of De of $$^{125}$$I$$^{-}$$ on salinity was uncertain. The cation excess and anion exclusion effects for Ca-montmorillonite were lower than those for Na-montmorillonite. The integrated sorption and diffusion (ISD) model, assuming the homogeneous pore structure and the electrical double layer (EDL) theory for 2:1 electrolyte (CaCl$$_{2}$$), could account for the observed trends for De in Ca-montmorillonite. The lower dependence of De on the porewater salinity in Ca-montmorillonite was caused by the reduction of the EDL thickness for divalent cations (Ca$$^{2+}$$) in comparison with that for monovalent cations (Na$$^{+}$$). The multipore model could improve the fit for De of $$^{125}$$I$$^{-}$$ at low salinity due to the reduction of interlayer pore volumes and anion exclusion effect, however, the disparity at higher densities was considerably larger. From these results, cation diffusion for compacted Ca-montmorillonite could be mainly explained by the electrostatic interactions in the homogeneous pore model; in contrast, anion diffusion was sensitive to both electrostatic interactions and heterogeneous pore structures. The proposed ISD model is an effective tool to evaluate the radionuclide diffusion and sorption behavior in both compacted Ca-montmorillonite and Na-montmorillonite.

論文

Pore distribution of compacted Ca-montmorillonite using NMR relaxometry and cryoporometry; Comparison with Na-montmorillonite

大窪 貴洋*; 山崎 秋雄*; 深津 勇太; 舘 幸男

Microporous and Mesoporous Materials, 313, p.110841_1 - 110841_11, 2021/01

 被引用回数:2 パーセンタイル:30.86(Chemistry, Applied)

Ca型モンモリロナイト中の間隙分布が、乾燥密度(0.8-1.6g/cm$$^{3}$$),間隙水塩濃度(脱イオン水、0.1及び1M CaCl$$_{2}$$),温度(233-303K)の条件下で、$$^{1}$$H NMR測定によって調査された。圧縮Ca型モンモリロナイト中の2層及び3層水和を含む層間間隙と層間外間隙の体積割合が、緩和時間$$T1$$及び$$T1/T2$$分布の分析に基づくNMR緩和時間測定法によって定量評価され、さらに、NMR凍結間隙測定法及びX線回折法による結果と比較された。これらの分析によって、Na型モンモリロナイトと比較可能な、Ca型モンモリロナイト中の間隙分布の状態を把握することができた。圧縮Ca型及びNa型モンモリロナイト中の間隙分布に影響を及ぼす主要な因子は圧縮密度であり、間隙水塩濃度の影響は相対的に小さい結果となった。CaとNaの層間陽イオンの影響は高密度条件では小さいが、低密度ではその影響は顕著であった。

口頭

グリムゼル花崗閃緑岩マトリクス中の原位置長期拡散試験の結果と解析

深津 勇太; 伊藤 剛志*; 舘 幸男; 石田 圭輔*; Martin, A.*

no journal, , 

高レベル放射性廃棄物の地層処分の安全評価において、室内試験によって構築された結晶質岩マトリクス中の核種移行モデルとパラメータの実際の地下環境下での適用性を確認することは重要な課題である。本研究では、スイスグリムゼル試験場での原位置長期拡散(Long-Term Diffusion: LTD)試験において、注入孔のトレーサー減衰データ、観測孔の破過データ及び岩石中の濃度プロファイルを取得するとともに、原位置試験と同じ岩石を用いた室内拡散試験データから、トレーサー試験孔の掘削時に生じる岩盤へのダメージ領域(Borehole Damaged Zone: BDZ)の影響や間隙率の差異を補正して原位置パラメータを推定する手法を適用した原位置試験結果の解析を行い、その適用性を評価した。

口頭

Modelling analysis on in situ Long Term Diffusion (LTD-II) test at the Grimsel test site

深津 勇太; 伊藤 剛志*; 舘 幸男; 石田 圭輔*; Martin, A.*

no journal, , 

In the safety assessment of geological disposal of high-level radioactive waste, it is an important task to confirm applicability of the models and parameters to quantify the radionuclide migration based on laboratory diffusion and sorption tests to the actual underground environment. In this study, the second Long-Term Diffusion (LTD-II) test at the GTS using tritiated water (HTO), Cl-36, Na-22, Cs-134 and Ba-133 as tracers were analysed focusing borehole disturbed zone (BDZ) effect near borehole and diffusion anisotropy by the foliation effect. We measured the detailed depth profile of the cations and wide-range distributions of HTO and Cl-36 around an injection hole by additional laboratory analysis, and in situ LTD-II test results were predicted by the scaling approach from laboratory to in situ condition.

口頭

An Overview and key results from the long term in situ diffusion project (ltd) at the Grimsel Test Site, Switzerland

Martin, A.*; 深津 勇太; 舘 幸男; 石田 圭輔*; Muuri, E.*; Siitari-Kauppi, M.*; Havlov$'a$, V.*; Vokal, A.*

no journal, , 

Diffusion and sorption parameters used in performance assessment calculations for assessing the long term safety of future radioactive waste repositories are typically derived from rock samples that are de-stressed once removed from the host rock. This can lead to an over-estimation of matrix diffusion and sorption from lab based experiments primarily due to sample preparation in comparison with actual conditions in crystalline rocks. Despite this, there have been very few long-term field-scale experiments to realistically evaluate matrix diffusion and sorption of radionuclides in fractured rock with minimal disturbance to in-situ conditions. These issues have formed the basis for the design of the Long Term Diffusion (LTD) project at the Grimsel Test Site (GTS) in Switzerland. The results and comparison to diffusion and sorption models, with a particular focus on scaling from lab to in situ conditions and process understanding will be overviewed in this paper.

口頭

粘土鉱物に吸着したCsのケミカルシフトと構造の関係

武井 滉洋*; 大窪 貴洋*; 舘 幸男; 深津 勇太

no journal, , 

天然の岩石や土壌中の放射性核種の移行を評価するうえで、風化生成物として含まれる粘土鉱物への放射性核種の吸着・固定は重要な現象のひとつである。放射性廃棄物の地層処分の安全評価や福島の環境中へ放出された核種の挙動評価において、重要な放射性核種であるCsは、主に粘土鉱物によって吸着・固定化される。岩石や土壌に含まれる代表的な粘土鉱物であるバーミキュライトはCsを強く吸着することが知られておりCsの移動挙動を支配する物質の一つである。バーミキュライトへのCsの吸着・脱着試験より、バーミキュライトは複数のCs吸着サイトが存在することが示唆されているが、その詳細なメカニズムについては解明されていない。そこで本研究では、Csが吸着したバーミキュライトの133Cs固体NMR実験とモデル構造によるシフト計算により、バーミキュライトに吸着したCsのケミカルシフトと構造の関係を調べた。

口頭

Investigation on diffusion of $$^{137}$$Cs$$^{+}$$, $$^{125}$$I$$^{-}$$ and HTO in compacted Ca-montmorillonite by experimental and modelling approaches

深津 勇太; 四辻 健治*; 大窪 貴洋*; 舘 幸男

no journal, , 

A compacted bentonite is an engineered barrier material in the geological disposal of radioactive waste. Na-montmorillonite (Na-MMT), which is main component of the bentonite, might be altered to Ca-montmorillonite (Ca-MMT) due to interaction with cementitious materials used in the geological repository. The alteration of the montmorillonite possibly causes decreasing the barrier performance of compacted bentonite such as a less swelling property and sorption capacity. The diffusion and sorption of various radionuclides were investigated by the integrated sorption and diffusion (ISD) model that we previously developed, as target on compacted Na-MMT. In this study, in order to evaluate influence of the alteration from Na-MMT to Ca-MMT on diffusion of radionuclides, diffusion behaviors of $$^{137}$$Cs$$^{+}$$, $$^{125}$$I$$^{-}$$ and HTO in compacted Ca-MMT were investigated by experimental and modelling approaches.

口頭

Pore connectivity of clay materials implicated in fluid flow and chemical diffusion

Hu, Q.*; Wang, Q.*; Zhao, C.*; 舘 幸男; 深津 勇太

no journal, , 

低透水粘土バリア材料中の低拡散性は、放射性廃棄物処分場の長期性能評価において、重要な安全機能と認識されている。間隙の連結性が低い低透水粘土材料は、特異な拡散特性を示し、このことが長期拡散挙動に影響を及ぼす可能性が報告されている。日本の幌延URLの稚内層の泥岩、スイスのモンテリURLのオパリナス粘土岩、さまざまな頁岩や粘土鉱物の関連研究において、間隙構造の評価手法(水銀圧入法や中性子小角散乱法など)と、レーザーアブレーションICP-MSによるマイクロスケールでの元素分布分析を組合せたトレーサー試験手法が適用された。これらの試験結果から、間隙の連続性と拡散挙動の特異性との関係が得られた。間隙のサイズは低い透水性や拡散性の主要な要因ではなく、特異な拡散挙動は間隙の連結性に起因していることを明らかにした。

口頭

Investigation on solute transport in heterogeneous fracture of crystalline rock by flow-through test and micro X-ray CT

深津 勇太; 舘 幸男

no journal, , 

Crystalline rocks such as granodiorites have been investigated as potential host rocks for the geological disposal of radioactive waste in many countries. Radionuclide transport in fractured crystalline rocks can be conceptualized by a dual-porosity model where radionuclides are transported by advective water flow through a fracture and are retarded by both diffusion and sorption into the surrounding rock matrix. Aperture variability within a fracture determines flow in a channel, whereas other areas of the fracture have almost stagnant water. The effect of different degrees of heterogeneity in fracture aperture distributions is critically important to quantify solute transport. In the present study, we identified flow channels and stagnant water zones in a fractured granodiorite by mean of a flow-through test, using imaging tracer coupled with micro X-ray CT measurements.

口頭

Quantifying isolated pore space in geological barrier materials

Hu, Q.*; Wang, Q.*; Oware, P.*; 舘 幸男; 深津 勇太; Ilavsky, J.*; Almer, J.*

no journal, , 

Pore connectivity is important in controlling fluid flow and mass transport in porous natural rocks. A different extent of pore connectivity can be reflected in the proportion of isolated pore space not connected to the surface of natural rocks. This work presents the multi-approach and multi-scale laboratory studies to investigating the proportion of isolated pore space of, and its resultant anomalous fluid flow and radionuclide movement in, generic geological barrier materials. The samples include mudstone from Wakkanai formation, Opalinus clay from Mt. Terri as well as granodiorite from Grimisel, salt rock from Waste Isolation Pilot Plant in New Mexico, and welded tuff in Yucca Mountain. The independent quantification of both (1) surface-accessible pore space with various probing fluids (e.g., micron-scale tracer mapping using laser ablation-ICP-MS); and (2) total porosity by small angle X-ray scattering. Our complementary approaches provide a rich toolbox for tackling the pore structure characteristics in geological barrier materials, and associated fluid flow and radionuclide transport.

口頭

Realistic modeling approach for tracer migration and retention in fractured crystalline rocks from the Grimsel Test Site

舘 幸男; 伊藤 剛志*; 深津 勇太; 赤木 洋介*; 佐藤 久夫*; Hu, Q.*; Martin, A. J.*

no journal, , 

In order to develop a realistic model and reliable parameters for long-term safety assessments of geological disposal, it is necessary to understand and quantify the effects of heterogeneities found around the fractures on RN transport processes in fractured crystalline rocks. This paper presents a comprehensive approach developed for coupling laboratory tests, microscopic observations and modeling in order to understand and quantify tracer transport processes occurring in natural fracture, using different types of fractured granodiorite sample from the Grimsel Test Site (GTS), Switzerland. Laboratory tests including through-diffusion, batch sorption and flow-through tests using five tracers with different retention properties indicated that tracer retention was consistently in the sequence of HDO $$<$$ Se $$<$$ Cs $$<$$ Ni $$<$$ Eu. Microscale heterogeneities around the fracture were clarified and quantified by coupling X-ray computed tomography and electron probe microanalysis. Realistic model incorporating heterogeneities around the fracture and their properties provided a much better interpretation for breakthrough curves of all tracers.

口頭

圧縮ベントナイト中の複数化学種共存下でのNp(V)拡散挙動評価

深津 勇太; 石寺 孝充; 舘 幸男

no journal, , 

放射性廃棄物の地層処分において、核種漏えいを抑制するためのバリア材として、Na型モンモリロナイトを主成分とした圧縮ベントナイトの使用が検討されている。これまでに、圧縮ベントナイトのバリア性能を評価するため、核種の移行度を示す実効拡散係数(De)及び収着分配係数(Kd)が取得され、圧縮ベントナイト中の拡散及び収着挙動の理解が進められてきた。しかしながら、対象とされてきた核種はCs$$^{+}$$やI$$^{-}$$などの一価の陽イオン及び陰イオンがほとんどであり、多価イオン核種の拡散及び収着挙動は十分に明らかになっていない。多価イオンは水溶液中で水酸化物イオンと錯体を形成することに加えて、地下水中に含まれる炭酸イオン(CO$$_{3}$$$$^{2-}$$)と錯体を形成する。したがって、多価イオンの拡散及び収着挙動の理解には、錯体形成による複数化学種共存下での拡散と収着を考慮するとともに、平衡反応による各化学種の存在割合の変化と拡散及び収着挙動の関係を評価することが重要である。Np(V)は、溶液中でNpO$$_{2}$$$$^{+}$$として存在し、CO$$_{3}$$$$^{2-}$$濃度の増加に伴いNpO$$_{2}$$CO$$_{3}$$$$^{-}$$の割合が高くなる。したがって、CO$$_{3}$$$$^{2-}$$濃度を制御した拡散試験により、NpO$$_{2}$$$$^{+}$$とNpO$$_{2}$$CO$$_{3}$$$$^{-}$$の存在割合の変化による拡散及び収着挙動への影響を評価することが可能となる。本研究では、CO$$_{3}$$$$^{2-}$$を含む溶液で飽和した圧縮ベントナイトを対象に、Np(V)の透過拡散試験を実施した。また、平衡反応によるNpO$$_{2}$$$$^{+}$$とNpO$$_{2}$$CO$$_{3}$$$$^{-}$$の存在割合の変化と拡散及び収着を考慮したシミュレーションを行い、実験データとの回帰分析から、圧縮ベントナイト中のNpO$$_{2}$$$$^{+}$$とNpO$$_{2}$$CO$$_{3}$$$$^{-}$$のDe及びKdを評価した。

口頭

Investigation of the effect of biotite distribution on anion diffusion in crystalline rock

深津 勇太; 舘 幸男

no journal, , 

Matrix diffusion in crystalline rocks is a key process for the retardation of radionuclide transport for geological disposal. Crystalline rocks mainly consist of quartz and alkaline feldspar grains and phyllosilicate minerals such as biotite. The biotite, randomly or regularly, distributed in the rock (foliation) could influence the diffusion of anion radionuclides due to the anion exclusion effect caused by its negatively charged surface. However, there is little information available about the effect of the content and distribution of biotite on anion exclusion in the matrix. In this study, through-diffusion tests with tritiated water (HTO) and anions (Cl$$^{-}$$ or I$$^{-}$$), together with micro X-ray CT analysis, were conducted on crystalline rocks containing biotite to obtain their effective diffusion coefficient (D$$_{e}$$) and determine the biotite content and distribution. The anion exclusion effect was evaluated by the ratio of D$$_{e}$$ of anion and HTO.

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Fluid flow and chemical transport in shallow and deep mudrocks being implicated by pore geometry and connectivity

Hu, Q.*; Wang, Q.*; Zhao, C.*; Zhang, T.*; 舘 幸男; 深津 勇太

no journal, , 

Fine-grained and clay-rich mudrocks play an important role in the long-term performance of a geological repository for storing high-level nuclear wastes and petroleum production in shale formations. However, low-permeability mudrocks whose pores are poorly interconnected are known to have anomalous diffusion properties that strongly impact long-term net diffusion. The complex pore structure involving predominantly nano-sized pore space is related to compaction and diagenesis from the maturation process of organic matter-rich mudrocks at deep depths, leading to a much smaller effective porosity which could be further partitioned by water- or oil-wet pore networks. Working with shallow clayey sediments of Wakkanai formation around Horonobe underground research center in Hokkaido of Japan and Opalinus clay of Mt. Terri Underground Research Laboratory in Switzerland, as well as various deep shales (Barnett, Eagle Ford and Wolfcamp from Texas, Bakken from North Dakota), using a wide range of sample sizes, this multi-approach and -scale work utilizes a complementary suite of approaches for pore structure characterization (e.g., helium pycnometry, mercury intrusion porosimetry, small angle/X-ray neutron scattering, field emission-scanning electron microscopy), gas diffusion and liquid (including water-, oil-, and bi-wetting) imbibition involving custom-designed tracer recipe followed with micro-scale mapping with laser ablation-ICP-MS. The experimental results show that deep mudrocks has a much smaller effective porosity than the total porosity (as a result of poor pore connectivity) and associated diffusion coefficient, and the effective porosity and diffusion coefficients are also dependent upon the sample sizes used in the measurement.

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Realistic modeling approach for radionuclide transport in heterogeneous fractured crystalline rocks

舘 幸男; 伊藤 剛志*; 深津 勇太; 赤木 洋介*; 佐藤 久夫*; Martin, A. J.*

no journal, , 

To develop a realistic model and reliable parameters for long-term safety assessments of geological disposal, it is necessary to understand and quantify the effects of heterogeneities around the fractures on radionuclide transport in fractured crystalline rocks. This paper presents a comprehensive approach developed for coupling laboratory tests, microscopic observations and modelling in order to understand and quantify tracer transport occurring in natural fracture, using different types of fractured granodiorite sample from the Grimsel Test Site, Switzerland. Realistic model incorporating heterogeneities around the fracture, and their properties such as porosity, sorption and diffusion parameters, provided a much better interpretation for experimental results of several tracers with different transport properties. Mechanistic understanding and detailed modeling considering the effects of heterogeneities around a natural fracture should improve confidence for the safety assessment in fractured crystalline rocks.

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