| 1. |
- Berglund, Sten, et al.
(författare)
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Identification and Characterization of Potential Discharge Areas for Radionuclide Transport by Groundwater from a Nuclear Waste Repository in Sweden
- 2013
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Ingår i: Ambio. - : Springer Nature. - 0044-7447 .- 1654-7209. ; 42:4, s. 435-446
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes solute transport modeling carried out as a part of an assessment of the long-term radiological safety of a planned deep rock repository for spent nuclear fuel in Forsmark, Sweden. Specifically, it presents transport modeling performed to locate and describe discharge areas for groundwater potentially carrying radionuclides from the repository to the surface where man and the environment could be affected by the contamination. The modeling results show that topography to large extent determines the discharge locations. Present and future lake and wetland objects are central for the radionuclide transport and dose calculations in the safety assessment. Results of detailed transport modeling focusing on the regolith and the upper part of the rock indicate that the identification of discharge areas and objects considered in the safety assessment is robust in the sense that it does not change when a more detailed model representation is used.
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| 2. |
- Bosson, Emma, et al.
(författare)
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Exchange and pathways of deep and shallow groundwater in different climate and permafrost conditions using the Forsmark site, Sweden, as an example catchment
- 2013
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Ingår i: Hydrogeology Journal. - : Springer Nature. - 1431-2174 .- 1435-0157. ; 21:1, s. 225-237
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Tidskriftsartikel (refereegranskat)abstract
- This study simulates and quantifies the exchange and the pathways of deep and shallow groundwater flow and solute transport under different climate and permafrost conditions, considering the example field case of the coastal Forsmark catchment in Sweden. A number of simulation scenarios for different climate and permafrost condition combinations have been performed with the three-dimensional groundwater flow and transport model MIKE SHE. Results show generally decreasing vertical groundwater flow with depth, and smaller vertical flow under permafrost conditions than under unfrozen conditions. Also the overall pattern of both the vertical and the horizontal groundwater flow, and the water exchange between the deep and shallow groundwater systems, change dramatically in the presence of permafrost relative to unfrozen conditions. However, although the vertical groundwater flow decreases significantly in the presence of permafrost, there is still an exchange of water between the unfrozen groundwater system below the permafrost and the shallow groundwater in the active layer, via taliks. ‘Through taliks’ tend to prevail in areas that constitute groundwater discharge zones under unfrozen conditions, which then mostly shift to net recharge zones (through taliks with net downward flow) under permafrost conditions.
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| 3. |
- Cvetkovic, Vladimir, et al.
(författare)
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Comparative measures of radionuclide containment in the crystalline geosphere
- 2002
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Ingår i: Nuclear science and engineering. - : Informa UK Limited. - 0029-5639 .- 1943-748X. ; 142:3, s. 292-304
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Tidskriftsartikel (refereegranskat)abstract
- A probabilistic model for assessing the capacity of a fractured crystalline rock volume to contain radionuclides is developed The rock volume is viewed as a network of discrete fractures through which radionuclides are transported by flowing water. Diffusive mass transfer between the open fractures and the stagnant water in the pore space of the rock matrix allow radionuclides access to mineral grains where physical and chemical processes-collectively known as sorption-can retain radionuclides. A stochastic Lagrangian framework is adopted to compute the probability that a radionuclide particle will be retained by the rock, i.e., the probability that it will decay before being released from the rock volume. A dimensionless quantity referred to as the containment index is related to this probability and proposed as a suitable measure for comparing different rock volumes; such a comparative measure may be needed, for example, in a site selection program for geological radioactive waste disposal. The probabilistic solution of the transport problem is based on the statistics of two Lagrangian variables: T, the travel time of an imaginary tracer moving with the flowing water, and beta, a suitably normalized surface area available for retention. Statistics of tau and beta may be computed numerically using site-specific discrete fracture MP network simulations. Fracture data from the well-characterized Aspo Hard Rock Laboratory site in southern Sweden are used to illustrate the implementation of the proposed containment index for six radionuclides (Sn-126, I-129, Cs-135, Np-237, Pu-239, and Se-79). It is found that fractures of small aperture imply prolonged travel times and hence long tails in both beta and tau. This, in turn, enhances retention and is favorable from a safely assessment perspective.
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| 4. |
- Cvetkovic, Vladimir, et al.
(författare)
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Inference of Retention Time From Tracer Tests in Crystalline Rock
- 2020
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 56:2
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Tidskriftsartikel (refereegranskat)abstract
- A statistical parametrization of transport combined with a new, general partition function for diffusive mass transfer (Cvetkovic, 2017, ) is here developed into a practical tool for evaluating tracer tests in crystalline rock. The research question of this study is how to separate the characteristic times of retention and advection, using tracer test information alone; this decoupling is critical for upscaling of transport. Three regimes are identified based on the unconditional mean number of trapping events. Analytical expressions are derived for inferring transport-retention parameters; these are first tested on a series of generic examples and then using two sets of tracer test data. Our results indicate that the key transport-retention parameters can be inferred separately with reasonable accuracy by a few simple steps, provided that the macrodispersion is not too large and retention not too strong. Of particular interest is inference of the retention time from the breakthrough curve peak that avoids costly asymptotic monitoring. Finally, we summarize the retention times as inferred from a series of nonsorbing tracer tests in the Swedish granite, demonstrating the uncertainties when estimating retention based on material and structural properties from samples. Possible strategies for reducing these uncertainties that combine improved understanding of crystalline rock evolution with numerical simulations are noted as topics for future research.
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| 5. |
- Cvetkovic, Vladimir, et al.
(författare)
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Stochastic simulation of radionuclide migration in discretely fractured rock near the Aspo Hard Rock Laboratory
- 2004
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 40:2, s. W02404-
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Tidskriftsartikel (refereegranskat)abstract
- We study the migration of sorbing tracers through crystalline rock by combining relatively simple transport measures with particle tracking in a discrete fracture network. The rock volume is on a 100 m scale and is a replica of a thoroughly characterized site at the Aspo Hard Rock Laboratory, Sweden. Flow is driven by generic boundary conditions consistent with the natural gradient in the region. The emphasis is on the global effect of fracture-to-fracture hydraulic variability where individual fractures are assumed to be of uniform aperture. The transport measures are conditioned on two random variables: the water residence time (tau) and a parameter which quantifies the hydrodynamic control of retention (beta). Results are illustrated for two radionuclides: technetium (strongly sorbing) and strontium (weakly sorbing). It is found that the assumption of streamline routing or full mixing at fracture intersections has comparatively little impact on transport. The choice of the cubic or quadratic hydraulic law (i.e., relation between transmissivity and aperture) strongly affects water residence times but has little impact on average transport since it does not affect the statistics of beta. If the statistics of beta are known, then the distribution of water residence time (tau) is of little importance for transport. We assess the applicability of a linearized model beta = tau/b(ret) using two different approaches to estimate the effective retention'' aperture 2b(ret): from transmissivity data and from fracture density and flow porosity data. Under some conditions, these conventional estimates may provide acceptable representation of transport. The results stress the need for further studies on upscaling of tau, beta distributions as well as on estimating effective parameters for hydraulic control of retention.
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| 6. |
- Cvetkovic, Vladimir, et al.
(författare)
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Water and solute transport along hydrological pathways
- 2012
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 48:6, s. W06537-
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Tidskriftsartikel (refereegranskat)abstract
- A Lagrangian framework for material transport along hydrological pathways is presented and consequences of statistically stationary space-time flow velocity variations on advective transport are investigated. The two specific questions addressed in this work are: How do temporal fluctuations affect forward and backward water travel time distributions when combined with spatial variability? and Can mass transfer processes be quantified using conditional probabilities in spatially and temporally variable flow? Space-time trajectories are studied for generic conditions of flow, with fully ergodic or only spatially ergodic velocity. It is shown that forward and backward distributions of advective water travel time coincide for statistically stationary space-time variations. Temporal variability alters the statistical structure of the Lagrangian velocity fluctuations. Once this is accounted for, integration of the memory function with the travel time distribution is applicable for quantifying retention. Further work is needed to better understand the statistical structure of space-time velocity variability in hydrological transport, as well as its impact on tracer retention and attenuation.
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| 7. |
- Davy, Philippe, et al.
(författare)
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Scaling of fractured rock flow. Proposition of indicators for selection of DFN based flow models
- 2023
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Ingår i: Comptes rendus Geoscience. - : Cellule MathDoc/CEDRAM. - 1631-0713 .- 1778-7025. ; 355
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Tidskriftsartikel (refereegranskat)abstract
- The objective of the paper is to better understand and quantify the flow structure in fractured rocks from flow logs, and to propose relevant indicators for validating, calibrating or even rejecting hydrogeological models. We first studied what the inflow distribution tells us about the permeability structure from a series of analyses: distribution of transmissivities as a function of depth, proportion of flowing sections as a function of section scale, and scaling of the arithmetically-averaged and geometrically-averaged permeability. We then define three indicators that describe few fundamental characteristics of the flow/permeability, whatever the scale: a percolation scale ls, the way permeability increases with scale above ls, and the variability of permeability. A 4th indicator on the representative elemental volume could in principle be defined but the data show that this volume/scale is beyond the 300 m investigated. We tested a series of numerical models built in three steps: the geo-DFN based on the observed fracture network, the open-DFN which is the part of the geo-DFN where fractures are open, and a transmissivity model applying on each fracture of the open-DFN (Discrete Fracture Network). The analysis of the models showed that the percolation scale is controlled by the open-DFN structure and that the percolation scale can be predicted from a scale analysis of the percolation parameter (basically, the third moment of the fracture size distribution that provides a measure of the network connectivity). The way permeability increases with scale above the percolation threshold is controlled by the transmissivity model and in particular by the dependence of the fracture transmissivity on either the orientation of the fractures via a stress-controlled transmissivity or their size or both. The comparison with data on the first two indicators shows that a model that matches the characteristics of the geo-DFN with an open fraction of 15% as measured adequately fits the data provided that the large fractures remain open and that the fracture transmissivity model is well selected. Most of the other models show unacceptable differences with data but other models or model combinations has still to be explored beforerejecting them. The third indicator on model variability is still problematic since the natural data show a higher variability than the models but the open fraction is also much more variable in the data than in the models.
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| 8. |
- Decramer, M, et al.
(författare)
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Asthma and COPID: differences and similarities - With special reference to the usefulness of budesonide/formoterol in a single inhaler (Symbicort (R)) in both diseases
- 2005
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Ingår i: International Journal of Clinical Practice. - : Hindawi Limited. - 1742-1241 .- 1368-5031. ; 59:4, s. 385-398
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Forskningsöversikt (refereegranskat)abstract
- Asthma and chronic obstructive pulmonary disease (COPD) both have a high prevalence worldwide and yet each condition remains underdiagnosed. Despite a number of common features, these inflammatory respiratory syndromes have distinct clinical outcomes. COPD represents a greater economic burden than asthma because it has a less favourable prognosis and is associated with greater morbidity and mortality. Therefore, it is important to distinguish between these two diseases at an early stage, so that appropriate therapy can be prescribed to prevent deterioration. However, effective treatments that may be used in both conditions can minimise the effects of misdiagnosis and maximise the impact of treatment without the associated complexity when both conditions occur together. The current review summarises the differences and similarities of asthma and COPD, in terms of risk factors, pathophysiology, symptoms and diagnosis, to provide greater understanding of the role of budesonide/ formoterol in a single inhaler in both diseases.
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| 9. |
- Doolaeghe, D., et al.
(författare)
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Controls on fracture openness and reactivation in Forsmark, Sweden
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- In crystalline bedrock, the open fraction of the fracture network constitutes the main pathways for fluids. Many observations point out that the state of stress influences the open fraction, likely indicating recent reactivation. But how this occurs is still unresolved. We analyse the conditions for fracture reactivation from fracture data collected in the uppermost 1 km of bedrock in Forsmark, Sweden. The open fraction is mainly correlated to the stress acting normally on the fracture but even away from critical failure, leading us to analyse the potential fluid pressure required for reactivation, P-c. We observe that 100% of the fractures are open when P-c is hydrostatic, and the ratio decreases exponentially to a plateau of similar to 17% when P-c is lithostatic and above. Exceptions are the oldest fractures, having a low open fraction independent of P-c. We suggest that these results reflect past pressure build-ups, potentially related to recent glaciations, and developing only if the preexisting open fraction is large enough.
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| 10. |
- Grenier, Christophe, et al.
(författare)
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Groundwater flow and heat transport for systems undergoing freeze-thaw : Intercomparison of numerical simulators for 2D test cases
- 2018
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Ingår i: Advances in Water Resources. - : Elsevier BV. - 0309-1708 .- 1872-9657. ; 114, s. 196-218
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Tidskriftsartikel (refereegranskat)abstract
- In high-elevation, boreal and arctic regions, hydrological processes and associated water bodies can be strongly influenced by the distribution of permafrost. Recent field and modeling studies indicate that a fully-coupled multidimensional thermo-hydraulic approach is required to accurately model the evolution of these permafrost-impacted landscapes and groundwater systems. However, the relatively new and complex numerical codes being developed for coupled non-linear freeze-thaw systems require verification.This issue is addressed by means of an intercomparison of thirteen numerical codes for two-dimensional test cases with several performance metrics (PMs). These codes comprise a wide range of numerical approaches, spatial and temporal discretization strategies, and computational efficiencies. Results suggest that the codes provide robust results for the test cases considered and that minor discrepancies are explained by computational precision. However, larger discrepancies are observed for some PMs resulting from differences in the governing equations, discretization issues, or in the freezing curve used by some codes.
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