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Soler, J. M.*; Keklinen, P.*; Pulkkanen, V.-M.*; Moreno, L.*; Iraola, A.*; Trinchero, P.*; Hokr, M.*; ha, J.*; Havlov, V.*; Trpkoov, D.*; et al.
Nuclear Technology, 209(11), p.1765 - 1784, 2023/11
Times Cited Count:2 Percentile:72.91(Nuclear Science & Technology)Tachi, Yukio
Kagaku To Kyoiku, 71(10), p.420 - 423, 2023/10
no abstracts in English
Arthur, R.*; Sasamoto, Hiroshi; Alt-Epping, P.*; Tachi, Yukio
Applied Geochemistry, 155, p.105707_1 - 105707_8, 2023/08
Times Cited Count:1 Percentile:62.05(Geochemistry & Geophysics)The experience gained in modeling the evolution, from past to present, of natural tracer profiles in geologic media can help support safety assessment of disposal concepts for radioactive wastes in deep geologic repository. Solute-transport models were developed in the present study using a forward modeling approach constrained by boundary conditions inferred from the paleo-hydrogeological evolution of the Horonobe area in Hokkaido, Japan. Apparent differences in transport behavior at the two boreholes location considered in this study, which were situated only about 1 km apart, appear to have resulted from relatively small differences in accessible porosity and hydraulic conductivity, which in turn may have been controlled by local differences in fracture density and fracture connectivity.
Yuan, X.*; Hu, Q.*; Lin, X.*; Zhao, C.*; Wang, Q.*; Tachi, Yukio; Fukatsu, Yuta; Hamamoto, Shoichiro*; Siitari-Kauppi, M.*; Li, X.*
Journal of Hydrology, 618, p.129172_1 - 129172_15, 2023/03
Times Cited Count:0 Percentile:0(Engineering, Civil)Okubo, Takahiro*; Takei, Akihiro*; Tachi, Yukio; Fukatsu, Yuta; Deguchi, Kenzo*; Oki, Shinobu*; Shimizu, Tadashi*
Journal of Physical Chemistry A, 127(4), p.973 - 986, 2023/02
Times Cited Count:1 Percentile:56.86(Chemistry, Physical)The identification of adsorption sites of Cs on clay minerals has been studied in the fields of environmental chemistry. The nuclear magnetic resonance (NMR) experiments allow direct observations of the local structures of adsorbed Cs. The NMR parameters of Cs, derived from solid-state NMR experiments, are sensitive to the local neighboring structures of adsorbed Cs. However, determining the Cs positions from NMR data alone is difficult. This paper describes an approach for identifying the expected atomic positions of Cs adsorbed on clay minerals by combining machine learning (ML) with experimentally observed chemical shifts. A linear ridge regression model for ML is constructed from the smooth overlap of atomic positions descriptor and gauge-including projector augmented wave (GIPAW) ab initio data. The Cs chemical shifts can be instantaneously calculated from the Cs positions on any clay layers using ML. The inverse analysis from the ML model can derive the atomic positions from experimentally observed chemical shifts.
Yotsuji, Kenji*; Tachi, Yukio; Sakuma, Hiroshi*; Kawamura, Katsuyuki*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 29(2), p.63 - 81, 2022/12
The understanding of the swelling phenomenon of montmorillonite is essential to predict the physical and chemical behavior of clay-based barriers in radioactive waste disposal systems. This study investigated the key factors controlling crystalline swelling behavior of montmorillonite with different interlayer counter-ions by molecular dynamics (MD) simulations. On the basis of the comparisons between MD simulated and experimental results, the water content in the interlayer in five homoionic (Na, K, Cs, Ca and Sr) montmorillonite was strongly correlated to the hydration number and the preference of an outer- or inner-sphere complex of each counter-ion. The detailed analysis for these results offer insights that the hydration number is controlled by the hydration free energy, the volume and the distribution of each interlayer counter-ion. The systematic MD simulations with virtually variable parameters clarified that the hydration free energy and the charge of interlayer counter- ions compete as influencing factors, and the control the formation rate of an outer-sphere complex of each counter-ion. The empirical relationships between these key factors will allow essential insights into predicting the swelling behavior of montmorillonite with different interlayer counter-ions.
Wang, Q.*; Hu, Q.*; Zhao, C.*; Yang, X.*; Zhang, T.*; Ilavsky, J.*; Kuzmenko, I.*; Ma, B.*; Tachi, Yukio
International Journal of Coal Geology, 261, p.104093_1 - 104093_15, 2022/09
Times Cited Count:5 Percentile:69.58(Energy & Fuels)Soler, J. M.*; Meng, S.*; Moreno, L.*; Neretnieks, I.*; Liu, L.*; Keklinen, P.*; Hokr, M.*; ha, J.*; Vetenk, A.*; Reimitz, D.*; et al.
Geologica Acta, 20(7), 32 Pages, 2022/07
Times Cited Count:3 Percentile:57.97(Geology)Task 9B of the SKB Task Force on Modelling of Groundwater Flow and Transport of Solutes in fractured rock focused on the modelling of experimental results from the LTDE-SD in situ tracer test performed at the sp Hard Rock Laboratory in Sweden. Ten different modelling teams provided results for this exercise, using different concepts and codes. Three main types of modelling approaches were used: (1) analytical solutions to the transport-retention equations, (2) continuum-porous-medium numerical models, and (3) microstructure-based models accounting for small-scale heterogeneity (i.e. mineral grains and microfracture distributions). The modelling by the different teams allowed the comparison of many different model concepts, especially in terms of potential zonations of rock properties (porosity, diffusion, sorption), such as the presence of a disturbed zone at the rock and fracture surface, the potential effects of micro- and cm-scale fractures.
Bateman, K.*; Murayama, Shota*; Hanamachi, Yuji*; Wilson, J.*; Seta, Takamasa*; Amano, Yuki; Kubota, Mitsuru*; Ouchi, Yuji*; Tachi, Yukio
Minerals (Internet), 12(7), p.883_1 - 883_20, 2022/07
Times Cited Count:0 Percentile:0.02(Geochemistry & Geophysics)Soler, J. M.*; Neretnieks, I.*; Moreno, L.*; Liu, L.*; Meng, S.*; Svensson, U.*; Iraola, A.*; Ebrahimi, K.*; Trinchero, P.*; Molinero, J.*; et al.
Nuclear Technology, 208(6), p.1059 - 1073, 2022/06
Times Cited Count:4 Percentile:45.99(Nuclear Science & Technology)The SKB Task Force is an international forum on modelling of groundwater flow and solute transport in fractured rock. The WPDE experiments are matrix diffusion experiments in gneiss performed at the ONKALO underground facility in Finland. Synthetic groundwater containing several conservative and sorbing tracers was injected along a borehole interval. The objective of Task 9A was the predictive modelling of the tracer breakthrough curves from the WPDE experiments. Several teams, using different modelling approaches and codes, participated in this exercise. An important conclusion from this exercise is that the modelling results were very sensitive to the magnitude of dispersion in the borehole opening, which is related to the flow of water. Focusing on the tails of the breakthrough curves, which are more directly related to matrix diffusion and sorption, the results from the different teams were more comparable.
Tachi, Yukio; Saito, Takumi*; Kirishima, Akira*
Nihon Genshiryoku Gakkai-Shi ATOMO, 64(5), p.290 - 295, 2022/05
no abstracts in English
Sugiura, Yuki; Suyama, Tadahiro*; Tachi, Yukio
JAEA-Data/Code 2021-017, 58 Pages, 2022/03
Sorption behavior of radionuclides (RNs) in buffer materials (bentonites), rocks and cementitious materials is one of the key processes in a safe geological disposal of radioactive waste because RNs migration in these materials is expected to be retarded by the sorption process. Therefore, it is necessary to understand the sorption process and develop a database compiling reliable data and mechanistic/predictive models so that reliable parameters can be set under a variety of geochemical conditions relevant to a performance assessment (PA). For this purpose, Japan Atomic Energy Agency (JAEA) has developed the database of sorption parameters in bentonites, rocks and cementitious materials. This sorption database (SDB) was firstly developed as an important basis for the H12 PA of a high-level radioactive waste disposal, and have been provided through the Web. JAEA has continued to improve and update the SDB in the view of potential future needs of data focusing on assuring the desired quality level and testing the usefulness of the databases for possible applications to the PA-related parameter setting. This report focuses on updating of the sorption database (JAEA-SDB) as a basis of integrated approach for the PA-related distribution coefficient (Kd) setting and development of mechanistic sorption models. This report also includes an overview of the database structure and contents. Kd data and their quality assurance (QA) results were updated from literature collected with wider ranges. As a result, 8,503 Kd data from 70 references related to the above-mentioned systems were added and the total number of Kd values in JAEA-SDB reached 79,072. The QA/classified Kd data reached about 75.4% for all Kd data in JAEA-SDB. The updated JAEA-SDB is expected to make it possible to give a basis for the next-step PA-related Kd setting.
Francisco, P. C. M.; Matsumura, Daiju; Kikuchi, Ryosuke*; Ishidera, Takamitsu; Tachi, Yukio
Environmental Science & Technology, 56(5), p.3011 - 3020, 2022/03
Times Cited Count:2 Percentile:29.93(Engineering, Environmental)Ochs, M.*; Dolder, F.*; Tachi, Yukio
Applied Geochemistry, 136, p.105161_1 - 105161_11, 2022/01
Times Cited Count:4 Percentile:66.78(Geochemistry & Geophysics)Various types of radioactive wastes and environments contain organic substances that can stabilize the aqueous complexes with radionuclides and therefore lead to a decrease of sorption. The present study focuses on testing a methodology to quantify sorption reduction factors (SRFs) in the presence of organic ligands for cement systems. Three approaches for the estimation of SRFs; (1) analogy with solubility enhancement factors, (2) radionuclide speciation based on the thermodynamic calculations, and (3) experimental sorption data in ternary systems, were coupled and tested for the representative organic ligands (ISA and EDTA) and selected key radionuclides (actinides). Our approach allows to critically evaluate the dependence of SRFs for various systems on the chosen method of quantification, in accordance with the data availability for a given systems. The reliable SRFs can only be derived from the sorption measurements in ternary systems. SRF often need to be derived in the absence of such direct evidence, and estimations need to be made based on analogies and speciation information. However, such estimates may be subject to substantial uncertainties.
Mei, H.; Aoyagi, Noboru; Saito, Takumi*; Kozai, Naofumi; Sugiura, Yuki; Tachi, Yukio
Applied Geochemistry, 136, p.105178_1 - 105178_8, 2022/01
Times Cited Count:11 Percentile:86.47(Geochemistry & Geophysics)Soler, J. M.*; Keklinen, P.*; Pulkkanen, V.-M.*; Moreno, L.*; Iraola, A.*; Trinchero, P.*; Hokr, M.*; ha, J.*; Havlov, V.*; Trpkoov, D.*; et al.
SKB TR-21-09, 204 Pages, 2021/11
Tachi, Yukio; Ito, Tsuyoshi*; Gylling, B.*
Water Resources Research, 57(11), p.e2020WR029335_1 - e2020WR029335_20, 2021/11
Times Cited Count:2 Percentile:18.22(Environmental Sciences)This paper focuses on the scaling approach for sorption and diffusion parameters from laboratory to in-situ conditions using the dataset of LTDE-SD experiment performed at the sp HRL. The near-surface heterogeneities at both fracture surface and rock matrix could be evaluated by conceptual model with high porosity and diffusivity, and sorption capacity, and their gradual change at the near-surface zones. The modelling results for non-sorbing Cl-36 and weak-sorbing Na-22 could validate the model concept and the parameter estimation of porosity and diffusivity, by considering the disturbed zone of 5 mm thickness with gradual parameter changes. The De values of these cationic and anionic tracers showed typical cation excess and anion exclusion effects. The modelling results for high sorbing tracers (Cs-137, Ra-226, Ni-63 and Np-237) with different sorption mechanism could confirm the validity of the scaling approaches of Kd values as a function of particle size and their relation to the near-surface disturbances.
Fukatsu, Yuta; Yotsuji, Kenji*; Okubo, Takahiro*; Tachi, Yukio
Applied Clay Science, 211, p.106176_1 - 106176_10, 2021/09
Times Cited Count:10 Percentile:75.92(Chemistry, Physical)Bateman, K.; Murayama, Shota*; Hanamachi, Yuji*; Wilson, J.*; Seta, Takamasa*; Amano, Yuki; Kubota, Mitsuru*; Ouchi, Yuji*; Tachi, Yukio
Minerals (Internet), 11(9), p.1026_1 - 1026_23, 2021/09
Times Cited Count:2 Percentile:23.36(Geochemistry & Geophysics)Wilson, J.*; Bateman, K.; Tachi, Yukio
Applied Geochemistry, 130, p.104979_1 - 104979_19, 2021/07
Times Cited Count:13 Percentile:59.93(Geochemistry & Geophysics)The concept of deep geological disposal will include the multiple use of cement-based materials. In the case of argillaceous host rocks, the presence of hyperalkaline cement porefluid results in the destabilization of primary minerals in the argillite, resulting in the development of a zone of alteration at cement-rock interfaces. The process understanding gained from experimental, analogue, and modelling studies has been reviewed, and remaining areas of uncertainty identified. Although there is a reasonably good understanding of the mineral assemblages that are likely to occur due to cement-rock interactions, there are still some areas where a degree of uncertainty remains, in particular: the evolution of cement-argillite interfaces at T 25C; the rates at which secondary minerals form; the extent of pore clogging due to secondary mineral precipitation; the implications of alteration for radionuclide transport.