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Journal Articles

3D-microstructure analysis of compacted Na- and Cs-montmorillonites with nanofocus X-ray computed tomography and correlation with macroscopic transport properties

Takahashi, Hiroaki*; Tachi, Yukio

Applied Clay Science, 168, p.211 - 222, 2019/02

 Times Cited Count:9 Percentile:48.17(Chemistry, Physical)

Microstructural and mass transport properties of compacted Na- and Cs-montmorillonites with different swelling properties were investigated by combining 3D microstructure analysis using nanofocus X-ray CT and diffusion measurement of HDO. The X-ray CT observations indicated that macropores in the dry state of compacted Na-montmorillonite are filled with gel phases, and the grain sizes of clay particles shifted toward smaller values through the saturation and swelling processes. By contrast, no gel phase and no decrease in the grain and pore volumes were observed for saturated Cs-montmorillonite. The geometrical factors of the macropores including tortuosity and geometric constrictivity of saturated Cs-montmorillonite determined by the X-ray CT was consistent with the corresponding values derived in the HDO diffusion test. In the case of Na-montmorillonite, the larger differences between the geometric factors evaluated by the X-ray CT and the diffusion tests can be explained by the electrostatic constrictivity factor and the additional geometrical factors in gel phase and interlayer that are smaller than the detection limit of the X-ray CT.

Journal Articles

Clay-based modeling approach to diffusion and sorption in the argillaceous rock from the Horonobe URL; Application to Ni(II), Am(III), and Se(IV)

Tachi, Yukio; Suyama, Tadahiro; Yotsuji, Kenji; Ishii, Yasuo; Takahashi, Hiroaki*

CMS Workshop Lectures, Vol.21, p.241 - 250, 2016/00

Sorption and diffusion of radionuclides in argillaceous rocks are key processes in the safe geological disposal. The diffusion and sorption behavior of Ni(II), Am(III) and Se(IV) in mudstone from the Horonobe URL were investigated by experimental and modeling approaches. Effective diffusivities obtained by the through-diffusion experiments were in the sequence of Cs$$^{+}$$, Ni$$^{2+}$$, HTO, I$$^{-}$$, Se(SeO$$_{4}$$$$^{2-}$$), Am(Am(CO$$_{3}$$)$$^{2-}$$) by comparison with the previous study. The distribution coefficient values were consistent with those obtained by batch sorption tests. These results were interpreted by the clay-based modeling approach coupling the thermodynamic sorption model assuming key contributions of clays (smectite and illite) and the diffusion model assuming the electrical double layer theory and the simplified pore model with size distribution. This clay-based model could provide reasonable account of observed trends and could be basically applicable for various radionuclides.

Journal Articles

Matrix diffusion and sorption of Cs$$^{+}$$, Na$$^{+}$$, I$$^{-}$$ and HTO in granodiorite; Laboratory-scale results and their extrapolation to the in situ condition

Tachi, Yukio; Ebina, Takanori*; Takeda, Chizuko*; Saito, Toshihiko*; Takahashi, Hiroaki*; Ouchi, Yuji*; Martin, A. J.*

Journal of Contaminant Hydrology, 179, p.10 - 24, 2015/08

 Times Cited Count:28 Percentile:73.72(Environmental Sciences)

Matrix diffusion and sorption are important processes in the assessment of radionuclide transport in crystalline rocks. Diffusion and sorption parameters for Cs$$^{+}$$, Na$$^{+}$$, I$$^{-}$$ and HTO were determined by through-diffusion and batch sorption experiments using granodiorite samples from the Grimsel Test Site, Switzerland. The De values were in the order Cs$$^{+}$$, Na$$^{+}$$, HTO, I$$^{-}$$. The capacity factor and Kd values show the same trends. The dual depth profiles for Cs$$^{+}$$ and Na$$^{+}$$ can be interpreted by a near-surface Kd increment. The microscopic analysis indicated that this is caused by high porosity and sorption capacities in disturbed biotite minerals on the sample surface. The Kd values derived from the dual profiles are likely to correspond to Kd dependence on the grain sizes of crushed samples in the batch experiments. The results of the in situ LTD experiments were interpreted reasonably well by using transport parameters derived from laboratory data and extrapolating them to in situ conditions.

Journal Articles

XAFS analysis of Ni diffused in compacted bentonite

Takahashi, Hiroaki; Nemoto, Kazuaki; Tachi, Yukio; Katayama, Misaki*; Inada, Yasuhiro*

2012-Nendo Ritsumeikan Daigaku Sogo Kagaku Gijutsu Kenkyu Kiko Sentan Kenkyu Shisetsu Kyoyo Sokushin Jigyo Seika Hokokusho (Internet), 2 Pages, 2013/00

The diffusion profiles of strongly sorbing nuclides such as Cm, Am, Ni, in a compacted bentonite show two parts with different slopes which cannot be fitted by simple one-dimensional diffusion model considering single species. The reason for this anomalous diffusion behavior is not understood. Some XANES spectral shape of Ni diffused in compacted montmorillonite, which is main content of bentonite, at relatively higher concentrated region exhibit slight broadening of a feature on the high-energy side of the white line. The broadening of a feature doesn't appear in the case of Ni aqueous solution and Ni-montmorillonite. These results indicate that the inner coordination geometry of the Ni(II) ion diffused in compacted montmorillonite at relatively higher concentrated region.

Journal Articles

3D X-ray CT and diffusion measurements to assess tortuosity and constrictivity in a sedimentary rock

Takahashi, Hiroaki; Seida, Yoshimi; Yui, Mikazu

Diffusion Fundamentals (Internet), 11(89), p.1 - 11, 2009/00

A high-resolution, 3D image of the interior of the sedimentary rock was obtained by means of nano-focus X-ray CT. Using computational methods to analyze the 3D microstructure of the rock, we presented the tortuosity and geometrical constrictivity. We also presented results on the tritiated water (HTO) diffusion tests and a mercury intrusion porosimetry (MIP) test performed on the rock. We have compared these results to understand the dominating parameters that control diffusion of HTO in the present system. These results suggest that the dominating parameters in the present system are not the constrictivity but the tortuosity and the diffusion-accessible porosity. The material considered in this study is the siliceous mudstones sampled from 500 m in depth at the Wakkanai formation around Horonobe underground research center under investigation in Japan to confirm of technical reliability for a deep geological disposal system for radioactive waste.

Oral presentation

Development of advanced reprocessing system using high selective and controllable precipitants

Noda, Kyoko*; Takao, Koichiro*; Sugiyama, Yuichi*; Harada, Masayuki*; Nogami, Masanobu*; Maruyama, Koichi*; Takahashi, Hiroaki*; Kim, S.-Y.; Sato, Makoto; Mineo, Hideaki; et al.

no journal, , 

We have been developing an advanced reprocessing system for spent FBR fuels based on precipitation method using pyrrolidone derivatives. In previous investigation, N-cyclohexyl-2-pyrrolidone (NCP) is used as a precipitant, which is able to precipitate selectively UO$$_{2}$$$$^{2+}$$ ions in HNO$$_{3}$$ solution, and a process consisting of two separation steps; selective U precipitation step and U-Pu co-precipitation step, was developed. In order to make the process more effective and more economical, we are now studying precipitation of U and Pu with other pyrrolidone derivatives. The outline of the study and main results obtained until now are shown in this presentation.

Oral presentation

Retardation behaviors of Se and Th in sedimentary rock with humic substance

Seida, Yoshimi; Tachi, Yukio; Kitamura, Akira; Takahashi, Hiroaki; Nakazawa, Toshiyuki*; Yamada, Norikazu*

no journal, , 

no abstracts in English

Oral presentation

Analysis of three-dimensional porous structure in hard shales of the Wakkanai formation by means of X-ray computed tomography

Takahashi, Hiroaki; Seida, Yoshimi; Miyahara, Kaname; Yui, Mikazu

no journal, , 

no abstracts in English

Oral presentation

Measurement of pore tortuosity and constrictivity in siliceous mudstones of the Wakkanai formation

Takahashi, Hiroaki; Seida, Yoshimi; Yui, Mikazu

no journal, , 

no abstracts in English

Oral presentation

Oral presentation

Study on diffusion mechanism of Ni in water-saturated, compacted Na- and Ca-montmorillonite

Takahashi, Hiroaki; Seida, Yoshimi*; Tachi, Yukio

no journal, , 

Ni diffusion experiment and microstructure analysis in compacted water-saturated Na- and Ca-montmorillonite were performed. Diffusion mechanism of Ni in the compacted montmorillonite was studied by means of analysis of diffusion profile of Ni, TEM/EDS, XRD, near-infrared absorption spectroscopy and X-ray CT.

Oral presentation

Development of sorption/diffusion data acquisition method for high sorbiong Am and Th in Horonobe sedimentary rock

Ishii, Yasuo; Takahashi, Hiroaki; Seida, Yoshimi*; Tachi, Yukio; Nakazawa, Toshiyuki*; Kurosawa, Seiichi*; Okazaki, Mitsuhiro*

no journal, , 

We have developed Sorption/Diffusion Data Acquisition Method for High Sorbiong Am and Th in Horonobe Sedimentary Rock.

Oral presentation

Sorption / diffusion data aquisition method development for high sorbing americium in compacted bentonite

Ishii, Yasuo; Takahashi, Hiroaki; Tachi, Yukio; Tomura, Tsutomu*; Nemoto, Kazuaki*; Okazaki, Mitsuhiro*

no journal, , 

Am(III) diffusion experiment were performed by reservoir depletion (RD) test method coupled with thin layer ID profile fitting in 0.1 or 0.5M NaCl / 0.05M NaHCO$$_{3}$$ - bentonite (kunipia-F) system. The Kd values were also measured using batch technique in the same experimental conditions. In an ordinary ID profile acquisition cutting the bentonite by scraper, the compacted bentonite sample can be cut into 100 $$mu$$m thick slices. Using this technique, it was possible to divide the ID profile into 10 $$mu$$m and therefore, to analyze diffusion distance layer larger than 50 $$mu$$m.

Oral presentation

Study on microscale pore structure of the crystalline rock from Grimsel Test Site and radionuclide diffusion into the rock

Takahashi, Hiroaki; Tachi, Yukio; Nemoto, Kazuaki

no journal, , 

A microstructure of the crystalline rock from Grimsel Test Site prepared by injection of Cs$$^+$$ ion and X-ray contrast media using centrifugal force was analyzed by micro focus X-ray CT and EPMA. These results were compared with the results of diffusion test of radionuclei to understand diffusion mechanism of the radionuclei in crystalline rock.

Oral presentation

Study of Ni diffusion mechanisms on compacted montmorillonite

Takahashi, Hiroaki; Nemoto, Kazuaki; Tachi, Yukio

no journal, , 

Ni(II) diffusion experiment and microstructure analysis in compacted water-saturated Na- and Ca-montmorillonite have been performed. Diffusion mechanism of Ni(II) in compacted montmorillonite has been studied by comparative analysis of Ni(II) diffusion profile, XRD analysis and XAFS analysis.

Oral presentation

Matrix diffusion and sorption of Cs$$^{+}$$, Na$$^{+}$$, I$$^{-}$$ and HTO in granodiorite; Laboratory results and their extrapolation to the in-situ condition

Tachi, Yukio; Ebina, Takanori*; Takahashi, Hiroaki; Nemoto, Kazuaki; Suyama, Tadahiro*; Martin, A.*

no journal, , 

Matrix diffusion and sorption of radionuclides in crystalline host rocks are key processes controlling safe geological disposal of radioactive waste. Diffusion and sorption parameters for Cs$$^{+}$$, Na$$^{+}$$, I$$^{-}$$ and HTO were determined by laboratory experiments using granodiorite samples from the Grimsel Test Site, Switzerland. The De values derived were in the order Cs$$^{+}$$ $$>$$ Na$$^{+}$$ $$>$$ HTO $$>$$ I$$^{-}$$. The capacity factor and Kd values show the same trends. Depth profiles of Cs$$^{+}$$ and Na$$^{+}$$ obtained by abrasing samples after a diffusion period showed typical dual profiles. The results of in-situ long-term diffusion tests at GTS were interpreted by using GoldSim code and transport parameters based on laboratory results and their extrapolations to in-situ conditions. These model calculations could the in-situ LTD results of Cs$$^{+}$$ and Na$$^{+}$$ reasonably well, although it was difficult to interpret HTO results. Key findings from these comparative studies between laboratory experiments and in-situ LTD tests were discussed.

Oral presentation

High-speed chemical analysis of nano-particle using inductively coupled plasma time-of-flight mass spectrometer

Horikoshi, Ko*; Numa, Rinka*; Tagomori, Hisaya*; Ito, Satomi; Takahashi, Hiroaki*; Hirata, Takafumi*

no journal, , 

no abstracts in English

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