Tachi, Yukio; Ito, Tsuyoshi*; Gylling, B.*
Water Resources Research, 57(11), 20 Pages, 2021/11
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.
Tachi, Yukio; Ito, Tsuyoshi*; Akagi, Yosuke*; Sato, Hisao*; Martin, A. J.*
Water Resources Research, 54(11), p.9287 - 9305, 2018/11
Effects of fine-scale surface alterations on radionuclide migration in fractured crystalline rocks were investigated by a comprehensive approach coupling a series of laboratory tests, microscopic observations and modelling, using a single fractured granodiorite sample from the Grimsel Test Site, Switzerland. Laboratory tests including through-diffusion, batch sorption and flow-through tests using five tracers indicated that tracer retention was consistently in the sequence of HDO, Se, Cs, Ni, Eu, and as well as showing the existence of a diffusion-resistance layer near the fracture surface, cation excess and anion exclusion effects for diffusion. Microscale heterogeneities in structural properties around the fracture were clarified quantitatively by coupling X-ray CT and EPMA. A three layer model including weathered vermiculite, foliated mica and undisturbed matrix layers, and their properties such as porosity, sorption and diffusion parameters, could provide a reasonable interpretation for breakthrough curves and concentration distributions near fracture surface of all tracers, measured in flow-through tests.
Water Resources Research, 54(5), p.3335 - 3356, 2018/05
Assessing the hydraulic connectivity of fractures by single-borehole investigations is crucial to radioactive waste disposal, but is still a challenge as such connectivity is difficult to measure directly. This study presents geological, hydrological, hydrochemical, and rock mechanical data for three faulted/fractured mudstones (the Koetoi, Wakkanai, and Palfris formations) and proposes a new methodology for assessing the hydraulic connectivity of fractures.
Illman, W. A.*; Liu, X.*; Takeuchi, Shinji; Yeh, T.-C. J.*; Ando, Kenichi*; Saegusa, Hiromitsu
Water Resources Research, 45(1), p.W01406_1 - W01406_18, 2009/00
Two large-scale cross-hole pumping tests were conducted at separate locations in deep boreholes at the Mizunami Underground Research Laboratory (MIU) construction site in central Japan. We analyze the two cross-hole tests using the transient hydraulic tomography (THT) code to compute the hydraulic conductivity () and specific storage () tomograms, as well as their uncertainties in three-dimensions. The equivalent and obtained using asymptotic analysis served as the initial parameter estimates for the 3D stochastic inverse modeling effort. Results show several, distinct high and low zones that are continuous over hundreds of meters, which appear to delineate fault zones and their connectivity. The THT analysis of the tests also identified a low zone which corresponds with a known fault zone trending NNW and has been found to compartmentalize groundwater flow at the site. These results corroborate well with several hydrogeological phenomena around the site.
Doughty, C.*; Tsang, C.-F.*; Hatanaka, Koichiro; Yabuuchi, Satoshi; Kurikami, Hiroshi
Water Resources Research, 44(8), p.W08403_1 - W08403_11, 2008/08
The flowing fluid electric conductivity (FFEC) logging method is an efficient way to provide information on the depths, salinities, and inflow strengths of individual conductive features intercepted by a borehole, without the use of specialized probes. The present paper presents the application of the method to two zones within a 1000-m borehole in sedimentary rock, which produced, for each zone, three sets of logs at different pumping rates, each set measured over a period of about one day.
Tsang, C.-F.*; Doughty, C.*; Uchida, Masahiro
Water Resources Research, 44(8), p.W08445_1 - W08445_13, 2008/08
no abstracts in English
Lim, D. H.
Water Resources Research, 42(2), p.W02601_1 - W02601_3, 2006/02
An extended random-walk reflection scheme taking into account the local mass conservation error around the interface between different materials is developed for the molecular diffusion in composite porous media with different porosity as well as with different diffusivity. The local mass conservation error is a physically infeasible gathering of mass around the interface, and is caused by random-walk simulations without proper treatments for discontinuity in hydraulic and transport properties such as porosity and diffusivity. In the random-walk reflection scheme, in order to conserve the mass at the interface, once particles reach the interface for a unit time step, the further displacements of particles for remaining time step are determined based on transition-probabilities whether these particles can be reflected at the interface or entered into another region. In the current study, the transition-probabilities are derived from the analytical solutions for the diffusion in the composite media. An extended random-walk reflection scheme incorporating the transition-probabilities is developed and compared with the analytical solutions. A selected previous study, i.e. generalized SDE (Stochastic Differential Equations) scheme, is also compared with the analytical solutions especially for the media with different porosity. The current study shows that i) the newly developed extended random-walk reflection scheme has a good agreement with the analytical solutions for the composite media with different porosity as well as with different diffusivity, while the generalized SDE scheme has a good agreement for the composite media with the same porosity or with the porosity ratio less than 1, ii) a random-walk scheme without completely solving the local mass conservation error causes numerical error such as an overestimation of the maximum release rate of mass.