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.

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.

Production of applicable and homogeneous biochar for soil amendment purposes would benefit from knowledge on how feedstock heterogeneity impacts key biochar pore properties and how the properties are transformed due to pyrolysis. This study aimed (1) to quantify how clonal differences and within-tree heterogeneity of a hybrid aspen feedstock (wood) impact biochar pore properties and (2) to estimate how pore properties of non-pyrolysed wood materials are transformed when pyrolysed into biochar. The study was conducted by collecting samples from a hybrid aspen (Populus tremula L. x Populus tremuloides Michx.) clonal field trial. Key pore properties of non-pyrolysed and pyrolysed wood samples were quantified with 3D X-ray imaging and quantitative image analyses. The results demonstrated how pyrolysis shifted distinctively bi-modal pore size distributions of the wood samples towards smaller pore size regions. The bi-modal wood tissue structure controlled the pore structure also in the biochars. Due to decreasing cell wall thicknesses, the pyrolysis increased the porosity of the materials. While the thermal process homogenized differences in the wall thicknesses, the thicknesses of the feedstock were also shown to control the resulting thicknesses in the biochars. Mechanisms of biochar pore property formation can be considered important when designing applicable biochars for a chosen purpose. Clonal differences and within-tree heterogeneity had a direct impact only on the wall thicknesses and the pore diameters of vessels. These impacts can be of interest when planning feedstock utilization in biochar production. However, the results suggest that relatively homogeneous biochar can be produced from hybrid aspen feedstocks.

The porosity distribution and mineralogical changes in a clay-rich fault core from the Tournemire underground research laboratory are analyzed to determine the mechano-chemical processes in a small-scale vertical strike-slip fault. The results display significant spatial variations in porosity and mineralogy along different gouge zones due to a polyphased tectonic history combined with complex paleo-fluid migrations. Porosity values increase from the center of the gouges to their borders indicating diffusive sealing/healing effects and past hydrothermal activities. The healing and thus the strengthening of the fault is marked by an increase of calcium content, which is concurrent with lower porosities around the gouge zone. Chemical mapping in the gouges reveal clay alteration, iron zonality and the presence of zinc sulphide as well as barium sulphate inside the gouge, further suggesting past hydrothermal activity. Finally, even though the observed porosity variations only occur in subcentimeter-thick gouge bands, the higher porosity sections are pathways for fluid flow during fault activity. © 5th International Conference on Fault and Top Seals 2019. All Rights Reserved.

Silicon-based mesoporous nanoparticles have been extensively studied to meet the challenges in the drug delivery. Functionality of these nanoparticles depends on their properties which are often changing as a function of particle size and surrounding medium. Widely used characterization methods, dynamic light scattering (DLS), and transmission electron microscope (TEM) have both their weaknesses. We hypothesize that conventional light scattering (LS) methods can be used for a rigorous characterization of medium sensitive nanoparticles’ properties, like size, stability, and porosity. Two fundamentally different silicon-based nanoparticles were made: porous silicon (PSi) from crystalline silicon and silica nanoparticles (SN) through sol-gel process. We studied the properties of these mesoporous nanoparticles with two different multiangle LS techniques, DLS and static light scattering (SLS), and compared the results to dry-state techniques, TEM, and nitrogen sorption. Comparison of particle radius from TEM and DLS revealed significant overestimation of the DLS result. Regarding to silica nanoparticles, the overestimation was attributed to agglomeration by analyzing radius of gyration and hydrodynamic radius. In case of PSi nanoparticles, strong correlation between LS result and specific surface area was found. Our results suggest that the multiangle LS methods could be used for the size, stability, and structure characterization of mesoporous nanoparticles.

The development of porosity during rock weathering is a key process controlling nutrients release, water holding capacity available for plants and water flow. Here we used X-ray Computed Tomography (XRCT) and 14C PolyMethylMethAcrylate (PMMA) autoradiography to show how cracks are created and enlarged during initial weathering stages (saprock and saprolite) of granodiorite in southern Brazil (Viama similar to o - RS). The physical evolution is characterized by imaging the pore network, using 14C-PMMA and XRCT methods. Combined with bulk porosity measurements, they highlight the increase in porosity with the degree of weathering (un-weathered rock phi = 1.66 %, saprolite phi = 11.7 %). This increase is related to the joint increase of the density of the cracks (unweathered rock D = 0.28 mm-1, saprolite D = 0.94 mm-1) and of the average opening of the microcracks (unweathered rock w = 2.4 mu m, saprolite w = 3.9 mu m) and macrocracks (un-weathered rock w = 176 mu m, saprolite w = 400 mu m). However, these average crack openings do not account for the variability of the openings that govern the flows, characterized here by specific distribution ranging from the submicrometre to the centimetre scale. The results highlight that the pore network of the un-weathered rock plays a key role in the initial stages or incipient weathering. The density and aperture and cracks increase following the subcritical cracking concept and new pores are formed by chemo-mechanical processes. The presence/absence of initial fractures in the regolith is certainly a key parameter controlling the weathering of different rock types (mafic vs felsic).