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; Ohuchi, Yuji; Martin, Andrew J.

doi:10.1016/j.jconhyd.2015.05.003

Cited by 38 publications

(43 citation statements)

References 48 publications

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“…As shown in Figure with the ratio of measured and modeled D e , the model could not express the D e trends observed in this study, larger diffusivities for cationic Cs + , and smaller diffusivities for anionic HSeO 3 − as compared with neutral HTO. The ratios of measured and modeled D e were consistent with the values observed for the previous results using the GTS rock in Tachi et al (). These observations indicate clearly that ionic diffusion in the GTS rock samples is due to cation excess and anion exclusion mechanisms.…”

Section: Resultssupporting

confidence: 90%

“…The K d dependences on the particle size for Cs are relatively small. Although the trends for Cs are different with the previous observed trends (Tachi et al, ), this may be explained by complex sorption mechanisms of Cs including ion exchange at basal plane and frayed edge sites, and their dependence on Cs concentration (e.g., Bradbury & Baeyens, ; Kyllönen et al, ; Muuri et al, ; Tachi et al, ).…”

Section: Resultsmentioning

confidence: 59%

“…The breakthrough curves in the outlet reservoir indicate a slower increase in concentration for these tracers with time for fracture sample. Although the tracer depletion in the inlet reservoir was not significant, the tracer‐depletion and breakthrough curves were fitted by a multiple curve analysis method (Tachi et al, , ; Tachi & Yotsuji, ) based on a rigorous analytical solution of equation (Hsieh et al, ; Zhang et al, ) assuming zero concentration for all tracers as initial condition, and concentration changes in both inlet and outlet reservoirs as boundary conditions. D e , α , and K d parameters were determined by simultaneous fitting of each of the two curves.…”

Section: Resultsmentioning

confidence: 99%

“…These cation excess and anion exclusion effects in D e trends have been widely observed in compacted montmorillonites and argillaceous rocks (e.g., Glaus et al, ; Tachi et al, , , ; Tachi & Yotsuji, ; Van Loon et al, , ). Based on the method used in Tachi et al (), D e values obtained for cations and anions were compared with those calculated by the conventional pore diffusion model, considered in terms of porosity ( ε ), tortuosity ( τ ), and geometric constrictivity ( δ g ) factor, and the tracer diffusivity in bulk liquid water, D w (m 2 /s), from Van Brakel and Heertjes ():

D_{e} = ε \frac{δ_{normalg}}{τ^{2}} D_{w} .

…”

Section: Resultsmentioning

confidence: 99%

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Effects of Fine‐Scale Surface Alterations on Tracer Retention in a Fractured Crystalline Rock From the Grimsel Test Site

Tachi

Ito

Akagi

et al. 2018

Water Resources Research

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Fine‐scale alterations found on fracture surfaces and between fracture surfaces and rock matrix are key uncertainties that need to be considered when developing solute transport models for 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 surfaces, 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 with different retention properties indicated that tracer retention was consistently in the sequence of HDO or HTO (deuterated or tritiated water) ≈ 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 around the fracture were clarified and quantified by coupling X‐ray computed tomography and electron probe microanalysis. A three‐layer model incorporating as much data as possible including weathered vermiculite, foliated mica, and undisturbed matrix layers, and their properties such as porosity, sorption, and diffusion parameters, obtained from laboratory diffusion tests and microscopic observations, provided a much better interpretation for breakthrough curves and concentration distributions near‐fracture surface of all tracers, measured in flow‐through tests, than either a one‐ or two‐layer model. Mechanistic understanding and detailed modeling considering the effects of fine‐scale surface alteration around a natural fracture should improve confidence for the safety assessment in fractured crystalline rocks.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 59%

Section: Resultsmentioning

confidence: 99%

D_{e} = ε \frac{δ_{normalg}}{τ^{2}} D_{w} .

…”

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Effects of Fine‐Scale Surface Alterations on Tracer Retention in a Fractured Crystalline Rock From the Grimsel Test Site

Tachi

Ito

Akagi

et al. 2018

Water Resources Research

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“…This exercise consisted of blind predictions based on model parameter setting from laboratory measurements and in situ porosity (Tachi et al, 2015). Five different cases were set by considering model and parameter variations.…”

Section: Codes and Setupmentioning

confidence: 99%

Comparative modeling of an in situ diffusion experiment in granite at the Grimsel Test Site

Soler

Landa

Havlová

et al. 2015

Journal of Contaminant Hydrology

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Modeling Transport of Cesium in Grimsel Granodiorite With Micrometer Scale Heterogeneities and Dynamic Update of K_d

Voutilainen

Kekäläinen

Siitari-Kauppi

et al. 2017

Water Resources Research

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Transport and retardation of cesium in Grimsel granodiorite taking into account heterogeneity of mineral and pore structure was studied using rock samples overcored from an in situ diffusion test at the Grimsel Test Site. The field test was part of the Long‐Term Diffusion (LTD) project designed to characterize retardation properties (diffusion and distribution coefficients) under in situ conditions. Results of the LTD experiment for cesium showed that in‐diffusion profiles and spatial concentration distributions were strongly influenced by the heterogeneous pore structure and mineral distribution. In order to study the effect of heterogeneity on the in‐diffusion profile and spatial concentration distribution, a Time Domain Random Walk (TDRW) method was applied along with a feature for modeling chemical sorption in geological materials. A heterogeneous mineral structure of Grimsel granodiorite was constructed using X‐ray microcomputed tomography (X‐μCT) and the map was linked to previous results for mineral specific porosities and distribution coefficients (Kd) that were determined using C‐14‐PMMA autoradiography and batch sorption experiments, respectively. After this the heterogeneous structure contains information on local porosity and Kd in 3‐D. It was found that the heterogeneity of the mineral structure on the micrometer scale affects significantly the diffusion and sorption of cesium in Grimsel granodiorite at the centimeter scale. Furthermore, the modeled in‐diffusion profiles and spatial concentration distributions show similar shape and pattern to those from the LTD experiment. It was concluded that the use of detailed structure characterization and quantitative data on heterogeneity can significantly improve the interpretation and evaluation of transport experiments.

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Matrix diffusion and sorption of Cs+, Na+, I– and HTO in granodiorite: Laboratory-scale results and their extrapolation to the in situ condition

Cited by 38 publications

References 48 publications

Effects of Fine‐Scale Surface Alterations on Tracer Retention in a Fractured Crystalline Rock From the Grimsel Test Site

Effects of Fine‐Scale Surface Alterations on Tracer Retention in a Fractured Crystalline Rock From the Grimsel Test Site

Comparative modeling of an in situ diffusion experiment in granite at the Grimsel Test Site

Modeling Transport of Cesium in Grimsel Granodiorite With Micrometer Scale Heterogeneities and Dynamic Update of K_d

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Matrix diffusion and sorption of Cs+, Na+, I– and HTO in granodiorite: Laboratory-scale results and their extrapolation to the in situ condition

Cited by 38 publications

References 48 publications

Effects of Fine‐Scale Surface Alterations on Tracer Retention in a Fractured Crystalline Rock From the Grimsel Test Site

Effects of Fine‐Scale Surface Alterations on Tracer Retention in a Fractured Crystalline Rock From the Grimsel Test Site

Comparative modeling of an in situ diffusion experiment in granite at the Grimsel Test Site

Modeling Transport of Cesium in Grimsel Granodiorite With Micrometer Scale Heterogeneities and Dynamic Update of Kd

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Modeling Transport of Cesium in Grimsel Granodiorite With Micrometer Scale Heterogeneities and Dynamic Update of K_d