Browsing by Subject "POROSITY"

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  • Voutilainen, Mikko; Kekäläinen, Pekka; Poteri, Antti; Siitari-Kauppi, Marja; Helariutta, Kerttuli; Andersson, Peter; Nilsson, Kersti; Byegård, Johan; Skålberg, Mats; Yli-Kaila, Maarit; Koskinen, Lasse (2019)
    In some countries the spent nuclear fuel produced by nuclear power plants will be deposited in crystalline granitic rock formations. In Finland, a repository for the spent nuclear fuel is being built at Olkiluoto. The safety assessment of the repository requires a careful determination of the transport properties of the bedrock. The porosity of the bedrock and the effective diffusion coefficients and distribution coefficients of different radio-nuclides for the bedrock are used as the main parameters in the safety assessment calculations. It has been questioned whether the parameters determined using laboratory experiments can be used to estimate the parameters in the in situ conditions. In this study, laboratory and in situ water phase diffusion experiments (WPDEs) were performed to resolve the issue. In the experiments, the transport of tritiated water (HTO), Cl-36, and Na-22 was studied using similar experimental setups. Mathematical models were constructed and solved to determine the transport parameters from the measured breakthrough curves. On average, the in situ WPDEs resulted in 20 (+/- 6)% smaller porosities and 32 (+/- 10)% smaller effective diffusion coefficients for HTO and Cl-36 than the laboratory WPDEs. It was also found that in veined gneiss, the most dominant rock type of the Olkiluoto bedrock, anion exclusion reduced the retention parameters of Cl-36 compared with those of HTO. Furthermore, the distribution coefficient of Na-22 for veined gneiss was 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.
  • Kohout, Tomas; Havrila, Karol; Toth, Juraj; Husarik, Marek; Gritsevich, Maria; Britt, Daniel; Borovicka, Jiri; Spurny, Pavel; Igaz, Antal; Svoren, Jan; Kornos, Leonard; Veres, Peter; Koza, Julius; Zigo, Pavol; Gajdos, Stefan; Vilagi, Jozef; Capek, David; Krisandova, Zuzana; Tomko, Dusan; Silha, Jiri; Schunova, Eva; Bodnarova, Marcela; Buzova, Diana; Krejcova, Tereza (2014)
    Bulk and grain density, porosity, and magnetic susceptibility of 67 individuals of Košice H chondrite fall were measured. The mean bulk and grain densities were determined to be 3.43 g/cm3 with standard deviation (s.d.) of 0.11 g/cm3 and 3.79 g/cm3 with s.d. 0.07 g/cm3, respectively. Porosity is in the range from 4.2 to 16.1%. The logarithm of the apparent magnetic susceptibility (in 10−9 m3/kg) shows narrow distribution from 5.17 to 5.49 with mean value at 5.35 with s.d. 0.08. These results indicate that all studied Košice meteorites are of the same composition down to ∼g scale without presence of foreign (non-H) clasts and are similar to other H chondrites. Košice is thus a homogeneous meteorite fall derived from a homogenous meteoroid.
  • Bonnet, M.; Sardini, P.; Billon, S.; Siitari-Kauppi, M.; Kuva, J.; Fonteneau, L.; Caner, L. (2020)
    Because cracks control the global mechanical and transport properties of crystalline rocks, it is of a crucial importance to suitably determine their aperture distribution, which evolves through alteration processes and rock weathering. Due to the high variability of crack networks in rocks, a multiscale approach is needed. The C-14-PMMA (polymethylmethacrylate) method was developed to determine crack apertures using a set of artificial crack samples with different controlled apertures and tilt angles and also using Monte Carlo simulations. The experiments and simulations show the same result: the estimation of apparent aperture w(A) was successful regardless of tilt angle, even if the estimates are less accurate for low tilt angles (
  • Puukko, Esa; Lehto, Jukka; Lindberg, Antero; Voutilainen, Mikko (2018)
    This study aims to determine upscaling factors for the radionuclides' distribution coefficients (Kd) on crushed rocks to intact rock for the safety analysis of radionuclide migration from spent nuclear fuel in bedrock towards biosphere. Here we report the distribution coefficients for intact rock determined by electromigration sorption experiments and compare the results with those from recently performed batch sorption experiments. In total 34 rock samples, representing three typical rock types from Olkiluoto Finland, were studied in order to determine distribution coefficients, effective diffusion coefficients and porosities using the electromigration sorption experiments, formation factor experiments and porosity measurement. The parameters determined represent the three main parameters of geosphere used in the safety assessment of spent nuclear fuel disposal. The distribution coefficients of cesium and strontium on intact rock varied between (0.12–26.2) × 10−3 m3/kg and (1.4–13.3) × 10−3 m3/kg, respectively, whereas recent results for crushed rock varied between (2–57) × 10−3 m3/kg and (17–40) × 10−3 m3/kg, respectively. This implies that crushing increases the distribution coefficient significantly and upscaling factors from 3 to 33 were determined for scaling the distribution coefficients of crushed rock to ones of intact rock. The determined distribution coefficients of cesium and strontium for intact rock can be directly applied in the safety assessment whereas the upscaling factors can be used to convert distribution coefficients determined for crushed rock into ones for intact rock. Based on the results for porosities and effective diffusion coefficients it was concluded that they do not seem to correlate with sorption parameters. However, an alteration state, heterogeneity and mineral content seem to be important factors affecting the distribution coefficients and upscaling factors.
  • Muuri, Eveliina; Sorokina, Tatiana; Donnard, Jerome; Billon, Sophie; Helariutta, Kerttuli; Koskinen, Lasse; Martin, Andrew; Siitari-Kauppi, Marja (2019)
    The spatial distribution of barium activity in granitic rocks was measured with two autoradiography techniques; digital autoradiography using phosphor imaging plate technique (Fuji 5100) and filmless electronic autoradiography (i.e. The BeaQuant (TM)), which is based on a gas detector incorporated in a micromesh Parallel Ionization Multiplier (PIM). Rock cubes taken from a diffusion experiment that were in contact with Ba-133 tracer were measured to determine diffusion profiles. In addition, the spatial distribution of Ba-133 in the samples was determined. Polymethyl methacrylate standards for Ba-133 were developed to determine the counting efficiency for electronic autoradiography. Good visual correlation between the two autoradiography methods were obtained in this study. The results of the experiments presented here can be utilized in future studies on the diffusion behavior of barium in granitic rocks.
  • Han, Liuyang; Tian, Xingling; Keplinger, Tobias; Zhou, Haibin; Li, Ren; Svedström, Kirsi; Burgert, Ingo; Yin, Yafang; Guo, Juan (2020)
    Structural and chemical deterioration and its impact on cell wall mechanics were investigated for visually intact cell walls (VICWs) in waterlogged archaeological wood (WAW). Cell wall mechanical properties were examined by nanoindentation without prior embedding. WAW showed more than 25% decrease of both hardness and elastic modulus. Changes of cell wall composition, cellulose crystallite structure and porosity were investigated by ATR-FTIR imaging, Raman imaging, wet chemistry, C-13-solid state NMR, pyrolysis-GC/MS, wide angle X-ray scattering, and N-2 nitrogen adsorption. VICWs in WAW possessed a cleavage of carboxyl in side chains of xylan, a serious loss of polysaccharides, and a partial breakage of beta -O-4 interlinks in lignin. This was accompanied by a higher amount of mesopores in cell walls. Even VICWs in WAW were severely deteriorated at the nanoscale with impact on mechanics, which has strong implications for the conservation of archaeological shipwrecks.
  • Kohout, T.; Kiuru, R.; Montonen, M.; Scheirich, P.; Britt, D.; Macke, R.; Consolmagno, G. (2011)
  • Kuva, J.; Voutilainen, M.; Mattila, K. (2019)
    The time domain-random walk method was developed further for simulating mass transfer in fracture flows together with matrix diffusion in surrounding porous media. Specifically, a time domain-random walk scheme was developed for numerically approximating solutions of the advection-diffusion equation when the diffusion coefficient exhibits significant spatial variation or even discontinuities. The proposed scheme relies on second-order accurate, central-difference approximations of the advective and diffusive fluxes. The scheme was verified by comparing simulated results against analytical solutions in flow configurations involving a rectangular channel connected on one side with a porous matrix. Simulations with several flow rates, diffusion coefficients, and matrix porosities indicate good agreement between the numerical approximations and analytical solutions.
  • Svensson, Urban; Voutilainen, Mikko; Muuri, Eveliina; Ferry, Michel; Gylling, Björn (2019)
    A numerical reactive transport model for crystalline rocks is developed and evaluated. The model is based on mineral maps generated by X-ray micro computed tomography (X-μCT); the maps used have a resolution of approximately 30 μm and the rock samples are on the cm scale. A computational grid for the intergranular space is generated and a micro-DFN (Discrete Fracture Network) model governs the grid properties. A particle tracking method (Time Domain Random Walk) is used for transport simulations. The basic concept of the model can now be formulated as follows; “when a particle is close to a reactive mineral surface it has a certain probability to get sorbed during a certain time span. Once sorbed it will remain so a certain time”. The model requires a number of input parameters that represent the sorption properties of the reactive minerals. Attempts are made to relate the parameters to traditional distribution parameters. The model is evaluated by comparisons with recent laboratory experimental data. These experiments consider two rock types (veined gneiss and pegmatitic granite) and two radionuclides (cesium and barium). It is concluded that the new reactive transport model can simulate the experimental data in a consistent and realistic way.
  • Rasa, Kimmo; Vihera-Aarnio, Anneli; Rytkonen, Peetu; Hyvaluoma, Jari; Kaseva, Janne; Suhonen, Heikki; Jyske, Tuula (2021)
    Novel bioeconomic approaches call for increasingly faster production of lignocellulosic biomass and its bettertailored use for higher added value. The high-yield capacity and structural properties of willows (Salix spp.) suggest their excellent potential for the production of designed biochar for use in agronomic, electronic and technical applications. All these applications rely on the internal pore structure of biochar. However, we lack an in-depth quantitative understanding of the interlinkages between the feedstock properties and the physical quality of the biochar produced. We studied quantitatively how the clonal and within-plant properties of five different willow clones (hybrids of Salix schwerinii E.L. Wolf) affected the micrometre-scale pore properties of the produced biochars (pyrolyzed at + 462 ?C). The porosity and pore size distribution were analysed before and after slow pyrolysis by X-ray microtomography and image analysis. We also studied the potential of conventional low-cost fibre analysis techniques to be used to predict biochar pore properties directly from fresh feedstock. The total porosity (0.55?0.62) and the pore size distribution of willow wood and derived biochars varied between clones. Approximately two-thirds of the biochar total porosity was associated with pores formed by wood fibres. Pyrolysis levelled off the structural variation detected between and within the clones. Pyrolysis-induced shrinkage reduced the pore sizes and narrowed the pore size distribution. The results suggest that conventional fibre analysis techniques could be utilized to predict biochar homogeneity. Short rotation coppice willows are suitable feedstock to produce homogenous biochar precursor for production of bio-based carbon materials to be used in high value-added technical applications. The structural homogeneity of the feedstock and produced biochar can be enhanced by selecting proper harvesting strategy and clones used in plantations. From the industrial perspective, comprehensive understanding of feedstock properties helps to control quality of the produced biochar.
  • Mirhashemihaghighi, Shadi; Swiatowska, Jolanta; Maurice, Vincent; Seyeux, Antoine; Klein, Lorena H.; Salmi, Emma; Ritala, Mikko; Marcus, Philippe (2016)
    Surface smoothening by substrate annealing was studied as a pre-treatment for improving the corrosion protection provided to copper by 10, 20 and 50 nm thick alumina coatings deposited by atomic layer deposition. The interplay between substrate surface state and deposited film thickness for controlling the corrosion protection provided by ultrathin barrier films is demonstrated. Pre-annealing at 750 degrees C heals out the dispersed surface heterogeneities left by electropolishing and reduces the surface roughness to less than 2 nm independently of the deposited film thickness. For 10 nm coatings, substrate surface smoothening promotes the corrosion resistance. However, for 20 and 50 nm coatings, it is detrimental to the corrosion protection due to local detachment of the deposited films. The weaker adherence of the thicker coatings is assigned to the stresses accumulated in the films with increasing deposited thickness. Healing out the local heterogeneities on the substrate surface diminishes the interfacial strength that is bearing the stresses of the deposited films, thereby increasing adhesion failure for the thicker films. Pitting corrosion occurs at the local sites of adhesion failure. Intergranular corrosion occurs at the initially well coated substrate grain boundaries because of the growth of a more defective and permeable coating at grain boundaries. (C) 2016 Elsevier B.V. All rights reserved.
  • Aromaa, Hanna; Voutilainen, Mikko; Ikonen, Jussi; Yli-Kaila, Maarit; Poteri, Antti; Siitari-Kauppi, Marja (2019)
    The spent nuclear fuel in Finland will be deposited in crystalline granitic rock in Olkiluoto, Finland. As a part of the safety assessment of the repository, series of extensive in-situ sorption and diffusion experiments and supplementary laboratory work has been done in the Olkiluoto site. Through Diffusion Experiment in a laboratory (TDElab) aims to provide applicable data for the ongoing in-situ experiment in Olkiluoto. This laboratory scale experiment resembles the in-situ experiment and aims to gain information on possible effects in values of distribution coefficients, effective diffusion coefficient and porosity that are caused by differences in laboratory and in-situ conditions. The through diffusion and sorption of tracer solution with known activities of HTO, 36Cl, 133Ba and 134Cs were studied in a decimeter scale sample of veined gneiss, which is one of the main rock types in Olkiluoto. The measured breakthrough curves were modeled taking into account the porosity of the rock and diffusion and sorption of the radionuclides using Time-Domain Random Walk (TDRW) simulations. The porosities of 0.7–0.8% were determined for the rock and effective diffusion coefficients of (3.5 ± 1.0) × 10−13 m2/s and (3.0 ± 1.0) × 10−13 m2/s were determined for HTO and 36Cl, respectively. The porosity and effective diffusion coefficients were found to be in agreement with previous results for veined gneiss. Furthermore, distribution coefficients of (1.0 ± 0.3) × 10−4 m3/kg and (2.0 ± 0.5) × 10−3 m3/kg were determined for 133Ba and 134Cs, respectively, using information about the effective diffusion coefficient determined for HTO. The distribution coefficients were found to be significantly smaller than the ones determined for crushed rock in previous studies and slightly smaller than the ones from previous in-diffusion experiments.
  • Kohout, Tomas; Karlqvist, Ronnie; Lassila, Ilkka Johannes; Eskelinen, Joona Juhani; Hortling, Airi; Pesonen, Lauri; Haeggström, Edward (2013)
    An ultrasonic method was tested to rapidly determine the porosity in custom made ceramic samples. The samples with porosities between 4 and 33% were of identical composition. The porosity estimates by ultrasonic method were validated against those obtained by helium and air pycnometry as well as with Archimedean method. The ultrasonic measurements can be performed rapidly (less than a minute) but they require a well prepared sample.