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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。
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.
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.