The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Ivars Neretnieks - One of the best experts on this subject based on the ideXlab platform.
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the effect of Stagnant Water zones on retarding radionuclide transport in fractured rocks an extension to the channel network model
Journal of Hydrology, 2016Co-Authors: Pirouz Shahkarami, Luis Moreno, Longcheng Liu, Ivars NeretnieksAbstract:Abstract An essential task of performance assessment of radioactive waste repositories is to predict radionuclide release into the environment. For such a quantitative assessment, the Channel Network Model and the corresponding computer program, CHAN3D, have been used to simulate radionuclide transport in crystalline bedrocks. Recent studies suggest, however, that the model may tend to underestimate the rock retarding capability, because it ignores the presence of Stagnant Water zones, STWZs, situated in the fracture plane. Once considered, the STWZ can provide additional surface area over which radionuclides diffuse into the rock matrix and thereby contribute to their retardation. The main objective of this paper is to extend the Channel Network Model and its computer implementation to account for diffusion into STWZs and their adjacent rock matrices. In the first part of the paper, the overall impact of STWZs in retarding radionuclide transport is investigated through a deterministic calculation of far-field releases at Forsmark, Sweden. Over the time-scale of the repository safety assessments, radionuclide breakthrough curves are calculated for increasing STWZ width. It is shown that the presence of STWZs enhances the retardation of most long-lived radionuclides except for 36 Cl and 129 I. The rest of the paper is devoted to the probabilistic calculation of radionuclide transport in fractured rocks. The model that is developed for transport through a single channel is embedded into the Channel Network Model and new computer codes are provided for the CHAN3D. The program is used to (I) simulate the tracer test experiment performed at Aspo HRL, STT-1 and (II) investigate the short- and long-term effect of diffusion into STWZs. The required data for the model are obtained from detailed hydraulic tests in boreholes intersecting the rock mass where the tracer tests were made. The simulation results fairly well predict the release of the sorbing tracer 137 Cs. It is found that over the short time-scale of the tracer experiment, the effect of diffusion into STWZs is not as pronounced as that of matrix diffusion directly from the flow channel, and the latter remains the main retarding mechanism. Predictions for longer time-scale, tens of years and more, show that the effect of STWZs becomes strong and tends to increase with transport time. It is shown that over the long times of interest for safety assessment of radioactive waste repositories, STWZs can substantially contribute to radionuclide retardation, though for the short time-scales the impact is not very strong and is not expected to affect the results of short-term field experiments.
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radionuclide migration through fractured rock for arbitrary length decay chain analytical solution and global sensitivity analysis
Journal of Hydrology, 2015Co-Authors: Pirouz Shahkarami, Luis Moreno, Ivars NeretnieksAbstract:Summary This study presents an analytical approach to simulate nuclide migration through a channel in a fracture accounting for an arbitrary-length decay chain. The nuclides are retarded as they diffuse in the porous rock matrix and Stagnant zones in the fracture. The Laplace transform and similarity transform techniques are applied to solve the model. The analytical solution to the nuclide concentrations at the fracture outlet is governed by nine parameters representing different mechanisms acting on nuclide transport through a fracture, including diffusion into the rock matrices, diffusion into the Stagnant Water zone, chain decay and hydrodynamic dispersion. Furthermore, to assess how sensitive the results are to parameter uncertainties, the Sobol method is applied in variance-based global sensitivity analyses of the model output. The Sobol indices show how uncertainty in the model output is apportioned to the uncertainty in the model input. This method takes into account both direct effects and interaction effects between input parameters. The simulation results suggest that in the case of pulse injections, ignoring the effect of a Stagnant Water zone can lead to significant errors in the time of first arrival and the peak value of the nuclides. Likewise, neglecting the parent and modeling its daughter as a single stable species can result in a significant overestimation of the peak value of the daughter nuclide. It is also found that as the dispersion increases, the early arrival time and the peak time of the daughter decrease while the peak value increases. More importantly, the global sensitivity analysis reveals that for time periods greater than a few thousand years, the uncertainty of the model output is more sensitive to the values of the individual parameters than to the interaction between them. Moreover, if one tries to evaluate the true values of the input parameters at the same cost and effort, the determination of priorities should follow a certain sequence.
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solute transport in fractured rocks with Stagnant Water zone and rock matrix composed of different geological layers model development and simulations
Water Resources Research, 2013Co-Authors: Batoul Mahmoudzadeh, Luis Moreno, Longcheng Liu, Ivars NeretnieksAbstract:A model is developed to describe solute transport and retention in fractured rocks. It accounts for the fact that solutes can not only diffuse directly from the flowing channel into the adjacent ro ...
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channeling with diffusion into Stagnant Water and into a matrix in series
Water Resources Research, 2006Co-Authors: Ivars NeretnieksAbstract:Numerous field observations show that most Water flow in fractured rocks takes place in only a small part of the fractures. We call these channels. Solutes in the flowing Water can diffuse in and out of Stagnant Water in the porous rock matrix that the flowing Water contacts via the so-called flow wetted surface (FWS). In addition, the solutes can diffuse into Stagnant Water in the fractures themselves and from this Water further into the rock matrix. For narrow channels with small FWS the transport via the Stagnant Water in the fracture can considerably add to the exchange of solutes between flowing Water and matrix Water. For sorbing solutes that interact with the micropore surfaces in the matrix the effect can be very strong. Some models that account for these processes are developed and solved using Laplace transforms. Some examples are presented that show the effects of first diffusion into Stagnant Waters in fractures with subsequent diffusion into the rock matrix. Effects of slit-like and tube-like channels are considered as well as the presence of intersecting fractures. The solutions are especially useful to model solute transport in complex three-dimensional channels networks where wide and narrow or even tube-like channels with widely varying flow rates combine into a multitude of different paths.
Merel B Soons - One of the best experts on this subject based on the ideXlab platform.
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the role of wind in the dispersal of floating seeds in slow flowing or Stagnant Water bodies
Journal of Vegetation Science, 2014Co-Authors: Judith M Sarneel, Boudewijn Beltman, Anneke Buijze, Roderick Groen, Merel B SoonsAbstract:QuestionWhat is the role of wind in the dispersal of Waterborne seeds in slow-flowing and Stagnant Water bodies at different temporal and spatial scales? (i) Is there a direct effect of wind on see ...
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post dispersal probability of germination and establishment on the shorelines of slow flowing or Stagnant Water bodies
Journal of Vegetation Science, 2012Co-Authors: Judith M Sarneel, Merel B SoonsAbstract:Question: In Dutch fens, species that colonize open Water and induce the formation of floating peat mats have become rare. Many such riparian pioneer species occur predominantly on shorelines sheltered from the wind, whereas the majority of seeds tend to be deposited on exposed shorelines, as seeds are dispersed via wind-driven waves and currents. Do differences in germination and seedling survival between sheltered and exposed shorelines explain this difference? Location: The fen reserve ‘De Westbroekse zodden’ (52 °10′ N; 5 °07′ E) Methods: With a sowing experiment, the germination, seedling survival and overall recruitment of Berula erecta, Calla palustris, Comarum palustre, Glyceria maxima and Mentha aquatica were studied on sheltered and wind-exposed banks in eight fen ponds. Temperature, light availability, Water level, wave impact, litter and seed deposition and vegetation height were recorded over 16 wk. The probability of washing away was quantified with small seed mimics. With a greenhouse experiment, we separately examined the effects of environmental differences between sheltered and exposed banks. Results: In the field, compared to sheltered shorelines, exposed shorelines had a higherwave impact, higher light availability in spring andmore litter and seeds deposited on them. In the greenhouse experiment, only litter addition decreased germination. This effect was overridden in the field, where the higher light availability on exposed banks increased germination. In the field, the number of seedlings decreased strongly over time, and eventual recruitment was determined by the degree to which seeds and seedlings were washed away by wave action. The probability of being washed away was highest on exposed shorelines (where waves were larger), which resulted in higher recruitment on sheltered shorelines. Conclusions: The recruitment of colonizing species to fen pond shorelines is limited by the probability that seeds and seedlings may be washed into the open Water. This process can eventually cause more successful recruitment on upwind or lee-side shorelines despite lower seed inputs there.
Luis Moreno - One of the best experts on this subject based on the ideXlab platform.
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the effect of Stagnant Water zones on retarding radionuclide transport in fractured rocks an extension to the channel network model
Journal of Hydrology, 2016Co-Authors: Pirouz Shahkarami, Luis Moreno, Longcheng Liu, Ivars NeretnieksAbstract:Abstract An essential task of performance assessment of radioactive waste repositories is to predict radionuclide release into the environment. For such a quantitative assessment, the Channel Network Model and the corresponding computer program, CHAN3D, have been used to simulate radionuclide transport in crystalline bedrocks. Recent studies suggest, however, that the model may tend to underestimate the rock retarding capability, because it ignores the presence of Stagnant Water zones, STWZs, situated in the fracture plane. Once considered, the STWZ can provide additional surface area over which radionuclides diffuse into the rock matrix and thereby contribute to their retardation. The main objective of this paper is to extend the Channel Network Model and its computer implementation to account for diffusion into STWZs and their adjacent rock matrices. In the first part of the paper, the overall impact of STWZs in retarding radionuclide transport is investigated through a deterministic calculation of far-field releases at Forsmark, Sweden. Over the time-scale of the repository safety assessments, radionuclide breakthrough curves are calculated for increasing STWZ width. It is shown that the presence of STWZs enhances the retardation of most long-lived radionuclides except for 36 Cl and 129 I. The rest of the paper is devoted to the probabilistic calculation of radionuclide transport in fractured rocks. The model that is developed for transport through a single channel is embedded into the Channel Network Model and new computer codes are provided for the CHAN3D. The program is used to (I) simulate the tracer test experiment performed at Aspo HRL, STT-1 and (II) investigate the short- and long-term effect of diffusion into STWZs. The required data for the model are obtained from detailed hydraulic tests in boreholes intersecting the rock mass where the tracer tests were made. The simulation results fairly well predict the release of the sorbing tracer 137 Cs. It is found that over the short time-scale of the tracer experiment, the effect of diffusion into STWZs is not as pronounced as that of matrix diffusion directly from the flow channel, and the latter remains the main retarding mechanism. Predictions for longer time-scale, tens of years and more, show that the effect of STWZs becomes strong and tends to increase with transport time. It is shown that over the long times of interest for safety assessment of radioactive waste repositories, STWZs can substantially contribute to radionuclide retardation, though for the short time-scales the impact is not very strong and is not expected to affect the results of short-term field experiments.
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radionuclide migration through fractured rock for arbitrary length decay chain analytical solution and global sensitivity analysis
Journal of Hydrology, 2015Co-Authors: Pirouz Shahkarami, Luis Moreno, Ivars NeretnieksAbstract:Summary This study presents an analytical approach to simulate nuclide migration through a channel in a fracture accounting for an arbitrary-length decay chain. The nuclides are retarded as they diffuse in the porous rock matrix and Stagnant zones in the fracture. The Laplace transform and similarity transform techniques are applied to solve the model. The analytical solution to the nuclide concentrations at the fracture outlet is governed by nine parameters representing different mechanisms acting on nuclide transport through a fracture, including diffusion into the rock matrices, diffusion into the Stagnant Water zone, chain decay and hydrodynamic dispersion. Furthermore, to assess how sensitive the results are to parameter uncertainties, the Sobol method is applied in variance-based global sensitivity analyses of the model output. The Sobol indices show how uncertainty in the model output is apportioned to the uncertainty in the model input. This method takes into account both direct effects and interaction effects between input parameters. The simulation results suggest that in the case of pulse injections, ignoring the effect of a Stagnant Water zone can lead to significant errors in the time of first arrival and the peak value of the nuclides. Likewise, neglecting the parent and modeling its daughter as a single stable species can result in a significant overestimation of the peak value of the daughter nuclide. It is also found that as the dispersion increases, the early arrival time and the peak time of the daughter decrease while the peak value increases. More importantly, the global sensitivity analysis reveals that for time periods greater than a few thousand years, the uncertainty of the model output is more sensitive to the values of the individual parameters than to the interaction between them. Moreover, if one tries to evaluate the true values of the input parameters at the same cost and effort, the determination of priorities should follow a certain sequence.
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solute transport in fractured rocks with Stagnant Water zone and rock matrix composed of different geological layers model development and simulations
Water Resources Research, 2013Co-Authors: Batoul Mahmoudzadeh, Luis Moreno, Longcheng Liu, Ivars NeretnieksAbstract:A model is developed to describe solute transport and retention in fractured rocks. It accounts for the fact that solutes can not only diffuse directly from the flowing channel into the adjacent ro ...
Pirouz Shahkarami - One of the best experts on this subject based on the ideXlab platform.
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the effect of Stagnant Water zones on retarding radionuclide transport in fractured rocks an extension to the channel network model
Journal of Hydrology, 2016Co-Authors: Pirouz Shahkarami, Luis Moreno, Longcheng Liu, Ivars NeretnieksAbstract:Abstract An essential task of performance assessment of radioactive waste repositories is to predict radionuclide release into the environment. For such a quantitative assessment, the Channel Network Model and the corresponding computer program, CHAN3D, have been used to simulate radionuclide transport in crystalline bedrocks. Recent studies suggest, however, that the model may tend to underestimate the rock retarding capability, because it ignores the presence of Stagnant Water zones, STWZs, situated in the fracture plane. Once considered, the STWZ can provide additional surface area over which radionuclides diffuse into the rock matrix and thereby contribute to their retardation. The main objective of this paper is to extend the Channel Network Model and its computer implementation to account for diffusion into STWZs and their adjacent rock matrices. In the first part of the paper, the overall impact of STWZs in retarding radionuclide transport is investigated through a deterministic calculation of far-field releases at Forsmark, Sweden. Over the time-scale of the repository safety assessments, radionuclide breakthrough curves are calculated for increasing STWZ width. It is shown that the presence of STWZs enhances the retardation of most long-lived radionuclides except for 36 Cl and 129 I. The rest of the paper is devoted to the probabilistic calculation of radionuclide transport in fractured rocks. The model that is developed for transport through a single channel is embedded into the Channel Network Model and new computer codes are provided for the CHAN3D. The program is used to (I) simulate the tracer test experiment performed at Aspo HRL, STT-1 and (II) investigate the short- and long-term effect of diffusion into STWZs. The required data for the model are obtained from detailed hydraulic tests in boreholes intersecting the rock mass where the tracer tests were made. The simulation results fairly well predict the release of the sorbing tracer 137 Cs. It is found that over the short time-scale of the tracer experiment, the effect of diffusion into STWZs is not as pronounced as that of matrix diffusion directly from the flow channel, and the latter remains the main retarding mechanism. Predictions for longer time-scale, tens of years and more, show that the effect of STWZs becomes strong and tends to increase with transport time. It is shown that over the long times of interest for safety assessment of radioactive waste repositories, STWZs can substantially contribute to radionuclide retardation, though for the short time-scales the impact is not very strong and is not expected to affect the results of short-term field experiments.
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radionuclide migration through fractured rock for arbitrary length decay chain analytical solution and global sensitivity analysis
Journal of Hydrology, 2015Co-Authors: Pirouz Shahkarami, Luis Moreno, Ivars NeretnieksAbstract:Summary This study presents an analytical approach to simulate nuclide migration through a channel in a fracture accounting for an arbitrary-length decay chain. The nuclides are retarded as they diffuse in the porous rock matrix and Stagnant zones in the fracture. The Laplace transform and similarity transform techniques are applied to solve the model. The analytical solution to the nuclide concentrations at the fracture outlet is governed by nine parameters representing different mechanisms acting on nuclide transport through a fracture, including diffusion into the rock matrices, diffusion into the Stagnant Water zone, chain decay and hydrodynamic dispersion. Furthermore, to assess how sensitive the results are to parameter uncertainties, the Sobol method is applied in variance-based global sensitivity analyses of the model output. The Sobol indices show how uncertainty in the model output is apportioned to the uncertainty in the model input. This method takes into account both direct effects and interaction effects between input parameters. The simulation results suggest that in the case of pulse injections, ignoring the effect of a Stagnant Water zone can lead to significant errors in the time of first arrival and the peak value of the nuclides. Likewise, neglecting the parent and modeling its daughter as a single stable species can result in a significant overestimation of the peak value of the daughter nuclide. It is also found that as the dispersion increases, the early arrival time and the peak time of the daughter decrease while the peak value increases. More importantly, the global sensitivity analysis reveals that for time periods greater than a few thousand years, the uncertainty of the model output is more sensitive to the values of the individual parameters than to the interaction between them. Moreover, if one tries to evaluate the true values of the input parameters at the same cost and effort, the determination of priorities should follow a certain sequence.
Judith M Sarneel - One of the best experts on this subject based on the ideXlab platform.
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the role of wind in the dispersal of floating seeds in slow flowing or Stagnant Water bodies
Journal of Vegetation Science, 2014Co-Authors: Judith M Sarneel, Boudewijn Beltman, Anneke Buijze, Roderick Groen, Merel B SoonsAbstract:QuestionWhat is the role of wind in the dispersal of Waterborne seeds in slow-flowing and Stagnant Water bodies at different temporal and spatial scales? (i) Is there a direct effect of wind on see ...
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post dispersal probability of germination and establishment on the shorelines of slow flowing or Stagnant Water bodies
Journal of Vegetation Science, 2012Co-Authors: Judith M Sarneel, Merel B SoonsAbstract:Question: In Dutch fens, species that colonize open Water and induce the formation of floating peat mats have become rare. Many such riparian pioneer species occur predominantly on shorelines sheltered from the wind, whereas the majority of seeds tend to be deposited on exposed shorelines, as seeds are dispersed via wind-driven waves and currents. Do differences in germination and seedling survival between sheltered and exposed shorelines explain this difference? Location: The fen reserve ‘De Westbroekse zodden’ (52 °10′ N; 5 °07′ E) Methods: With a sowing experiment, the germination, seedling survival and overall recruitment of Berula erecta, Calla palustris, Comarum palustre, Glyceria maxima and Mentha aquatica were studied on sheltered and wind-exposed banks in eight fen ponds. Temperature, light availability, Water level, wave impact, litter and seed deposition and vegetation height were recorded over 16 wk. The probability of washing away was quantified with small seed mimics. With a greenhouse experiment, we separately examined the effects of environmental differences between sheltered and exposed banks. Results: In the field, compared to sheltered shorelines, exposed shorelines had a higherwave impact, higher light availability in spring andmore litter and seeds deposited on them. In the greenhouse experiment, only litter addition decreased germination. This effect was overridden in the field, where the higher light availability on exposed banks increased germination. In the field, the number of seedlings decreased strongly over time, and eventual recruitment was determined by the degree to which seeds and seedlings were washed away by wave action. The probability of being washed away was highest on exposed shorelines (where waves were larger), which resulted in higher recruitment on sheltered shorelines. Conclusions: The recruitment of colonizing species to fen pond shorelines is limited by the probability that seeds and seedlings may be washed into the open Water. This process can eventually cause more successful recruitment on upwind or lee-side shorelines despite lower seed inputs there.
