Imaging connected porosity of crystalline rock by contrast agent‐aided X‐ray microtomography and scanning electron microscopy

Kuva, Jukka; Sammaljärvi, Juuso; Parkkonen, Joni; Siitari-Kauppi, Marja; Lehtonen, M.; Turpeinen, Tuomas; Timonen, J.; Voutilainen, Mikko

doi:10.1111/jmi.12661

Cited by 16 publications

(12 citation statements)

References 68 publications

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“…Most of the grain boundaries were found to be non-porous in applied scale (magnification: ×1000). The partly pinitized cordierite grains found are known to have high porosity and thus they are likely pronounced in the C-14-PMMA autoradiography (Kuva et al 2018;Sammaljärvi et al 2017).…”

Section: Scanning Electron Microscopymentioning

confidence: 95%

“…The total porosity of the REPRO-VGN sample was 0.26 %, consisting mostly of intragranular porosity as the number of micrometer scale grain boundary pores is minor. The highly porous grains in the autoradiograph originate from the partly pinitized cordierites (Sammaljärvi et al 2017;Kuva et al 2018) that were identified using FE-SEM-EDS. The abundance of the partly pinitized cordierite grains is 1.0 % which is lower than generally observed in VGN samples from the REPRO site (Sammaljärvi et al 2017).…”

Section: C-14-pmma Autoradiographymentioning

confidence: 99%

“…In a study by Kuva et al (2018), it was shown that the X-ray attenuation of the partly pinitized cordierite grains overlap with the quartz and feldspar grains. Thus the mixed mineral phase contains here also these cordierite grains.…”

Section: X-ray Micro Computed Tomographymentioning

confidence: 99%

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Characterization of spatial porosity and mineral distribution of crystalline rock using X-ray micro computed tomography, C-14-PMMA autoradiography and scanning electron microscopy

Voutilainen

Miettinen

Sardini

et al. 2019

Applied Geochemistry

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The spatial porosity and mineral distribution of geological materials strongly affects transport processes in them.X-ray micro computed tomography (X-μCT) has proven to be a powerful tool for characterizing the spatial mineral distribution of geological samples in 3-D. However, limitations in resolution prevent an accurate characterization of pore space especially for tight crystalline rock samples and 2-D methods such as C-14polymethylmethacrylate (C-14-PMMA) autoradiography and scanning electron microscopy (SEM) are needed.The spatial porosity and mineral distributions of tight crystalline rock samples from Äspö, Sweden, and Olkiluoto, Finland, were studied here. The X-μCT were used to characterize the spatial distribution of the main minerals in 3-D. Total porosities, fracture porosities, fracture densities and porosity distributions of the samples were determined using the C-14-PMMA autoradiography and characterization of mineral-specific porosities were assisted using chemical staining of rock surfaces. SEM and energy dispersive X-ray spectroscopy (EDS) were used to determine pore apertures and identify the minerals. It was shown that combination of the different imaging techniques creates a powerful tool for the structural characterization of crystalline rock samples. The combination of the results from different methods allowed the construction of spatial porosity, mineral and mineral grain distributions of the samples in 3-D. These spatial distributions enable reactive transport modeling using a more realistic representation of the heterogeneous structure of samples. Furthermore, the realism of the 2 spatial distributions were increased by determinig the densities and porosities of fractures and by the virtual construction heterogeneous mineral distributions of minerals that cannot be separated by X-μCT.

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Section: Scanning Electron Microscopymentioning

confidence: 95%

Section: C-14-pmma Autoradiographymentioning

confidence: 99%

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Characterization of spatial porosity and mineral distribution of crystalline rock using X-ray micro computed tomography, C-14-PMMA autoradiography and scanning electron microscopy

Voutilainen

Miettinen

Sardini

et al. 2019

Applied Geochemistry

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“…Cordierite, muscovite, chlorite and sillimanite are also found as minor components in VGN samples from REPRO site [37]. The mineral composition of the bedrock has been shown to be an important factor for the overall sorption properties of the rock [41,42,43,19].…”

Section: Rock Samples and Description Of The Experimental Sitementioning

confidence: 98%

Comparison of water phase diffusion experiments in laboratory and in situ conditions

Voutilainen

Kekäläinen

Poteri

et al. 2019

Journal of Hydrology

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In some countries, the spent nuclear fuel produced by nuclear power plants will be deposited in crystalline granitic rock formations. In Finland, such repository is being built at Olkiluoto. The safety assessment of the repository requires a careful determination of transport properties of the bedrock. Porosity of the rock and effective diffusion coefficient and distribution coefficients of different radionuclides for the bedrock are used as the main parameters in safety assessment calculations. It has been questioned if the parameters determined using laboratory experiments can be used to estimate the parameters in the in-situ conditions. Water Phase Diffusion Experiments (WPDE) performed in the laboratory and in-situ conditions were addressed to resolve this questions. In the experiments, transport of HTO, 36 Cl and 22 Na were studied using similar experimental setups in both conditions. Analytic models were constructed and solved to determine the transport parameters from the measured breakthrough curves. The in-situ WPDE resulted from 12 % to 38 % smaller porosities and from 30 % to 60 % smaller effective diffusion coefficients for HTO and 36 Cl than the laboratory WPDE. It was also shown that anion exclusion reduced the transport parameters of 36 Cl compared with the parameters of HTO in veined gneiss that is the most dominant rock type of Olkiluoto bedrock. Furthermore, the distribution coefficients of 22 Na for veined gneiss were found to be about one order of magnitude smaller in the in-situ conditions than in previous laboratory batch sorption experiments. The effects of the results on the safety assessment were evaluated and discussed.

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“…(1982). Furthermore, it has been shown that pore structure and heterogeneity may play an important role in the transport of radionuclides in crystalline rock samples (Sammaljärvi et al., 2017; Kuva et al., 2018).…”

Section: Introductionmentioning

confidence: 99%

Batch sorption experiments of cesium and strontium on crushed rock and biotite for the estimation of distribution coefficients on intact crystalline rock

Lehto

Puukko

Lindberg

et al. 2019

Heliyon

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The distribution coefficient (K d) of radionuclides on bedrock is one of the key parameters used in the safety analysis of spent nuclear fuel repositories. Typically, distribution coefficients have been determined using crushed rock. However, recent studies have shown that crushing of the rock increases considerably the distribution coefficient compared with the values of intact rock. This study aimed to test if batch sorption experiments using different grain sizes (i.e. mean diameter of grains) can be used to evaluate the K d of strontium (Sr) and cesium (Cs) on intact crystalline rock, which would decrease the needed experimental time compared with transport experiments. Here we report the results of the batch sorption experiments with crushed rocks and compare the results with those from a recent study performed using electromigration experiments with intact drill core samples (Puukko et al., 2018). The batch sorption experiments were done for rock samples from Olkiluoto, Finland, as a function of grain size and of Cs and Sr concentration. Furthermore, the specific surface areas of the same rock samples with different grain sizes were determined. It was shown that Cs distribution coefficients correlate with specific surface areas of the studied rocks and biotite, the correlation coefficient being 0.95. The Cs distribution coefficient was highest for biotite at about 0.1 m 3 /kg at 10 À4 M cesium concentration and increased systematically to about 1 m 3 /kg at 10 À8 M. Distribution coefficients for rocks were up to about two orders of magnitude lower, being lowest with the rock with the lowest biotite content (3.3%). The distribution coefficient of Sr varied from 0.04 m 3 /kg to 0.007 m 3 /kg and behaved in a different manner: it remained constant in two out of three studied rocks in the concentration range of 10 À8-10 À4 M and only in the case of one rock a decreasing trend was seen at the higher concentration range. It was also shown that batch sorption experiments overestimate the distribution coefficient in respect to intact rock. The decrease of the distribution coefficient as a function of grain size can be estimated using a power law function. It was also shown that estimation of distribution coefficients of Cs and Sr for intact rock by extrapolation of distribution coefficients determined for different grain sizes is not possible without increasing grain size, but in that case diffusion into the grains would also affect the results. A new method was developed for estimating the fraction of the inner surface area of the total surface area of crushed grains. For the mean grain sizes of 0.25 mm and 0.75 mm the fraction of the inner surface was found to be 35-70% and 60-90%, respectively. The inner specific surface area was highest with biotite at 1.2 m 2 /g and lowest with the rock with lowest biotite content (3.3%) at 0.07 m 2 /g. The surface area analysis revealed that crushing creates and/or allows access to additional inner surface area that is not measured in intact rock. Furthermore, it was demonstr...

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Imaging connected porosity of crystalline rock by contrast agent‐aided X‐ray microtomography and scanning electron microscopy

Cited by 16 publications

References 68 publications

Characterization of spatial porosity and mineral distribution of crystalline rock using X-ray micro computed tomography, C-14-PMMA autoradiography and scanning electron microscopy

Characterization of spatial porosity and mineral distribution of crystalline rock using X-ray micro computed tomography, C-14-PMMA autoradiography and scanning electron microscopy

Comparison of water phase diffusion experiments in laboratory and in situ conditions

Batch sorption experiments of cesium and strontium on crushed rock and biotite for the estimation of distribution coefficients on intact crystalline rock

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