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, Mikko; Miettinen, Arttu; Sardini, Paul; Parkkonen, Joni; Sammaljärvi, Juuso; Gylling, Björn; Selroos, Jan-Olof; Yli-Kaila, Maarit; Koskinen, Lasse; Siitari-Kauppi, Marja

doi:10.1016/j.apgeochem.2018.12.024

Cited by 26 publications

(14 citation statements)

References 46 publications

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“…In the laboratory WPDE for PGR, the effect of anion exclusion was not observed. In previous studies by Sammaljärvi et al [37] and Voutilainen et al [58], it has been shown that VGN and PGR samples from REPRO site differ considerably with respect to pore space and mica and clay mineral content. In VGN, the pore space consists mostly of inter-lamellar pores in mica minerals (biotite, muscovite and chlorite).…”

Section: Discussionmentioning

confidence: 89%

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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Section: Discussionmentioning

confidence: 89%

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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“…(2018) have shown that the samples studied in the here have a volumetric porosity ranging from 0.1% to 0.3%. In intact samples, the interfaces of the pores and minerals of the rock form the inner surface area that is available for sorption of radionuclides (Voutilainen et al., 2019b). The specific inner surface area (S i) was estimated in the following way:The grains were assumed to be spheres with a mean diameter of grains (d).…”

Section: Methodsmentioning

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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“…Previously Voutilainen et al [30] have resolved the 3D mineral structure of the samples with X-μCT and determined the porosity distribution with C-14-PMMA autoradiography. Furthermore, they have constructed 3D grain maps of the samples by first segmentating different main mineral phases from each other by their X-ray attenuation coefficient and then grains from mineral phases by running a watershed algorithm on 3D mineral phase images.…”

Section: Rock Samplesmentioning

confidence: 99%

“…Here a numerical method will be used to analyze grain properties by considering one gray scale value at the time and then add up a range of gray scale values to get the properties of a mineral phase. The starting point of the procedure is the 3D grain maps obtained by Voutilainen et al [30]. The analysis is carried out using the numerical groundwater flow and solute transport code DarcyTools [20,21].…”

Section: Grain and Mineral Surface Analysismentioning

confidence: 99%

“…Note that here the grain size is not defined as typically in crystallography. Here the fissures, fractures and grain boundaries are considered to divide crystallographic grains into multiple grains (for further details see Voutilainen et al [30]). Some numerical aspects of the calculation of grain surface area and shape factor are given in "Appendix".…”

Section: Grain and Mineral Surface Analysismentioning

confidence: 99%

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Grains, grids and mineral surfaces: approaches to grain-scale matrix modeling based on X-ray micro-computed tomography data

Svensson¹,

Trinchero

Ferry³

et al. 2019

SN Appl. Sci.

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X-ray micro-computed tomography (X-μCT) generates 3D mineral distribution maps currently with a resolution of about 10 μm. For tight crystalline rocks, this implies that the mineral grains are well resolved, while micro-fractures, having apertures of less than 10 μm, are not resolved. In this study, we propose a method to analyze the properties (size, volume, surface area) of the mineral grains based on X-μCT data. The numerical approach uses a resolution similar to that of the X-μCT data and hence shares the same limitations. For example, it is clear that a large fraction of the mineral surface area is due to so-called roughness, with scales below 10 μm. In the second part of the study, methods to generate the diffusion-available pore space are discussed. The inter-granular space (distance between grains) is often smaller than 10 μm, and we need to design methods to be able to perform diffusion simulations in the matrix. Three methods, all based on X-μCT, are discussed, and it is demonstrated that models with realistic global properties (mean porosity and effective diffusion coefficient) can be developed based on the suggested techniques.

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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

Cited by 26 publications

References 46 publications

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

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

Grains, grids and mineral surfaces: approaches to grain-scale matrix modeling based on X-ray micro-computed tomography data

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