scholarly journals A MiniSandwich Experiment with Blended Ca-Bentonite and Pearson Water—Hydration, Swelling, Solute Transport and Cation Exchange

Minerals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1061
Author(s):  
Katja Emmerich ◽  
Eleanor Bakker ◽  
Franz Königer ◽  
Christopher Rölke ◽  
Till Popp ◽  
...  
Keyword(s):  
Solute Transport ◽  
Cation Exchange ◽  
Numerical Models ◽  
Chloride Concentration ◽  
Injection Pressure ◽  
Sodium Concentration ◽  
Opalinus Clay ◽  
Hydraulic Permeability ◽  
Data Set ◽  
Clay Formation

Shaft seals are geotechnical barriers in nuclear waste deposits and underground mines. The Sandwich sealing system consists of alternating sealing segments (DS) of bentonite and equipotential segments (ES). MiniSandwich experiments were performed with blended Ca-bentonite (90 mm diameter and 125 mm height) to study hydration, swelling, solute transport and cation exchange during hydration with A3 Pearson water, which resembles pore water of Opalinus Clay Formation at sandy facies. Two experiments were run in parallel with DS installed either in one-layer hydrate state (1W) or in air-dry two-layer hydrate (2W) state. Breakthrough at 0.3 MPa injection pressure occurred after 20 days and the fluid inlet was closed after 543 days, where 4289 mL and 2984 mL, respectively, passed both cells. Final hydraulic permeability was 2.0–2.7·10−17 m2. Cells were kept for another 142 days before dismantling. Swelling of DS resulted in slight compaction of ES. No changes in the mineralogy of the DS and ES material despite precipitated halite and sulfates occurred. Overall cation exchange capacity of the DS does not change, maintaining an overall value of 72 ± 2 cmol(+)/kg. Exchangeable Na+ strongly increased while exchangeable Ca2+ decreased. Exchangeable Mg2+ and K+ remained nearly constant. Sodium concentration in the outflow indicated two different exchange processes while the concentration of calcium and magnesium decreased potentially. Concentration of sulfate increased in the outflow, until it reached a constant value and chloride concentration decreased to a minimum before it slightly increased to a constant value. The available data set will be used to adapt numerical models for a mechanism-based description of the observed physical and geochemical processes.

scholarly journals Claystone formations in Germany: what we (don't) know about them and how we can change this

2021 ◽  
Vol 1 ◽  
pp. 47-48
Author(s):  
Bernhard Schuck ◽  
Tilo Kneuker
Keyword(s):  
Phase I ◽  
Nuclear Waste ◽  
Site Selection ◽  
Numerical Models ◽  
Selection Procedure ◽  
Opalinus Clay ◽  
Nuclear Waste Repository ◽  
Fracture Density ◽  
Clay Formation

Abstract. Deep geological formations are considered for safe long-term disposal of high-level radioactive waste. Such a repository would be requested to prevent radionuclides from entering the biosphere for a period of 1 million years (StandAG, 2017). Consequently, a holistic characterization including lithological, mineralogical, geochemical, hydrological, structural and geomechanical properties of any potential repository-hosting rock formation is required. Nine claystone formations have been identified as “sub-areas” within the German site-selection procedure (BGE, 2020). The area covered by these formations comprises about half of the total area considered as being qualified for further exploration. However, despite its relevance to act as a geological barrier for, e.g. hydrocarbons or radionuclides, the characterization of clay-rich formations at depths exceeding 300 m in Germany has attained substantially less attention than economically more relevant units hosted by, e.g. sandstones or rock salt, which have been intensively explored. The BGR project BASTION aims at contributing to characterizing these claystone formations and emphasizes properties relevant to host a repository for nuclear waste. Investigations comprise (micro)structural/petrographic, mineralogical, geochemical, geophysical, hydraulic and thermomechanical analyses. In project phase I (2013–2019), claystones deposited in Northern Germany during the Lower Cretaceous were studied. These rocks belong to the fourth largest sub-area hosting claystones. Two of the main foci were to explore variations in lithology, mineralogy and geochemistry, and to identify deformation mechanisms (natural and artificial) by microstructural analyses. Although rocks appeared to be quite homogeneous on the 10–100 m scale, the results revealed distinct structural and sedimentary heterogeneities on the meter scale affecting fracture density. Another sub-area located in Southern Germany hosts the Opalinus Clay Formation (OPA). This up to 150 m thick claystone formation was deposited during the Middle Jurassic (Franz and Nitsch, 2009). Owing to its self-sealing capacity and ability to retain fluids, it is supposed to host the nuclear waste repository of Switzerland (Bossart et al., 2017). The OPA is quite well understood in terms of its lithology and (bio)stratigraphy, and there have been mineralogical, hydrological and petrophysical analyses, mostly documented in university theses a few decades old and sometimes difficult to access. However, it is questionable to what extent these investigations reflect the situation at depths relevant for the site-selection procedure. Well-documented data on the OPA and its properties relevant for nuclear waste disposal are available via the Swiss site-selection procedure (Bossart et al., 2017). However, as there remain substantial questions regarding the nature of the German portions of the OPA (e.g. spatial distribution of lithology, mineralogy, microstructures) at depths greater than a few decameters, it is unclear to what degree insights obtained in the Swiss site-selection procedure also account for Germany. Therefore, phase II of BASTION, which began in 2020, aims to use the multidisciplinary approach developed during phase I to characterize properties of the OPA relevant for the save long-term disposal of nuclear waste by identifying and quantifying structural and rheological heterogeneities. This will constitute important input for numerical models in any long-term safety assessment.

Numerical modeling of hydro-mechanical coupled effects in the cyclic deformation (CD-A) experiment: First results and comparison with observations

2021 ◽  
Author(s):  
Tuanny Cajuhi ◽  
Gesa Ziefle ◽  
Jobst Maßmann ◽  
Markus Furche
Keyword(s):  
Cyclic Deformation ◽  
Unsaturated Flow ◽  
Temporal Evolution ◽  
Numerical Models ◽  
Climatic Conditions ◽  
Opalinus Clay ◽  
Northwestern Part ◽  
Tunnel Wall ◽  
Clay Formation ◽  
Mont Terri

<p>The Mont Terri rock laboratory is situated in a clay formation in the northwestern part of Switzerland and is the place of several research focused experiments. These experiments enable the study of relevant coupled effects in the Opalinus Clay formation, an important material in the context of radioactive waste management due to its possible use as geological barrier. Our study focuses on the cyclic deformation (CD-A) experiment, which aims at investigating the coupled hydro-mechanical (HM) behavior of the material, e.g. shrinkage, swelling, changes in permeability. These processes can affect the stability and integrity of the rock. The experiment encompasses seasonal variations such as natural cyclic humidity changes due to winter and summer and consists of two niches. While one niche is open to the influence of the surroundings and hence, subjected to the effects of the seasonal changes of air humidity, the other niche is kept under controlled, high humidity conditions. Long-term quasi-continuous as well as repeating measurements for parameters such as relative humidity, water content, temperature, electrical resistivity and deformation, e.g. tunnel wall convergence via laser scans, are carried out amongst others (start in October 2019). These monitoring data are used as input for calibration and validation of numerical models.</p><p>In this contribution we numerically model the HM coupled effects in the context of the CD-A experiment using a macroscopic poromechanical approach. The mathematical model consists of the mass balance of the solid and the liquid phases with displacements and pore pressure as independent variables. Furthermore, it considers unsaturated flow by the Richards approximation. The model is solved numerically with the finite element method using the open-source software OpenGeoSys (OGS 6). Based on a literature review on the material properties of the clay sandy facies and experimental data, a two-dimensional model has been setup stepwise considering (i) in-situ initial pore water pressures and stresses, (ii) the effect of excavation, (iii) the experimentally based seasonal climatic conditions in the niches and (iv) the effect of bedding-induced anisotropy on the HM coupled behavior. With this numerical investigation, we evaluate the temporal evolution of the unsaturated zone. The Nuclear Magnetic Resonance (NMR), Electric Resistivity Tomography (ERT) and Taupe measurements indicate the spatial and temporal evolution of the seasonal hydraulic effects near the niches within the first experimental year. A first comparative study indicates qualitative agreement between monitored ERT data and simulation results and offers paths for model improvement and extension such as in the context of shrinkage-induced cracking.</p>

scholarly journals Osmotically inactive sodium and potassium storage: lessons learned from the Edelman and Boling data

2016 ◽  
Vol 311 (3) ◽  
pp. F539-F547 ◽  
Author(s):  
Minhtri K. Nguyen ◽  
Dai-Scott Nguyen ◽  
Minh-Kevin Nguyen
Keyword(s):  
Linear Regression ◽  
Measurement Errors ◽  
Linear Regression Analysis ◽  
Sodium Concentration ◽  
Lessons Learned ◽  
Dynamic Changes ◽  
Data Set ◽  
Storage Pool ◽  
Total Body ◽  
Sodium And Potassium

Because changes in the plasma water sodium concentration ([Na+]pw) are clinically due to changes in the mass balance of Na+, K+, and H2O, the analysis and treatment of the dysnatremias are dependent on the validity of the Edelman equation in defining the quantitative interrelationship between the [Na+]pw and the total exchangeable sodium (Nae), total exchangeable potassium (Ke), and total body water (TBW) (Edelman IS, Leibman J, O'Meara MP, Birkenfeld LW. J Clin Invest 37: 1236–1256, 1958): [Na+]pw = 1.11(Nae + Ke)/TBW − 25.6. The interrelationship between [Na+]pw and Nae, Ke, and TBW in the Edelman equation is empirically determined by accounting for measurement errors in all of these variables. In contrast, linear regression analysis of the same data set using [Na+]pw as the dependent variable yields the following equation: [Na+]pw = 0.93(Nae + Ke)/TBW + 1.37. Moreover, based on the study by Boling et al. (Boling EA, Lipkind JB. 18: 943–949, 1963), the [Na+]pw is related to the Nae, Ke, and TBW by the following linear regression equation: [Na+]pw = 0.487(Nae + Ke)/TBW + 71.54. The disparities between the slope and y-intercept of these three equations are unknown. In this mathematical analysis, we demonstrate that the disparities between the slope and y-intercept in these three equations can be explained by how the osmotically inactive Na+ and K+ storage pool is quantitatively accounted for. Our analysis also indicates that the osmotically inactive Na+ and K+ storage pool is dynamically regulated and that changes in the [Na+]pw can be predicted based on changes in the Nae, Ke, and TBW despite dynamic changes in the osmotically inactive Na+ and K+ storage pool.

Mitigation of Vortex-Induced Motions in a Monocolumn Platform

2009 ◽  
Author(s):  
Andre´ L. C. Fujarra ◽  
Rodolfo T. Gonc¸alves ◽  
Fernando Faria ◽  
Marcos Cueva ◽  
Kazuo Nishimoto ◽  
...  
Keyword(s):  
Model Test ◽  
Numerical Models ◽  
Cross Flow ◽  
Important Data ◽  
Data Set ◽  
Concept Model ◽  
Flow Motion

A great deal of works has been developed on the Spar VIM issue. There are, however, very few published works concerning VIM of monocolumn platforms, partly due to the fact that the concept is fairly recent and the first unit was only installed last year. In this context, the present paper presents a meticulous study on VIM for this type of platform concept. Model test experiments were performed to check the influence of many factors on VIM, such as different headings, wave/current coexistence, different drafts, suppression elements, and the presence of risers. The results of the experiments presented here are inline and cross-flow motion amplitudes, ratios of actual oscillation and natural periods, and motions in the XY plane. This is, therefore, a very extensive and important data set for comparisons and validations of theoretical and numerical models for VIM prediction.

Validation of Mooring Simulations (for Mooring Integrity Assessment) With In-Service Tension Measurements

2021 ◽  
Author(s):  
Willemijn Pauw ◽  
Remco Hageman ◽  
Joris van den Berg ◽  
Pieter Aalberts ◽  
Hironori Yamaji ◽  
...  
Keyword(s):  
Numerical Models ◽  
Weather Conditions ◽  
Mooring Line ◽  
Mooring System ◽  
Mooring Lines ◽  
Data Set ◽  
Integrity Assessment ◽  
Motion Data ◽  
Load Cells ◽  
Line Loads

Abstract Integrity of mooring system is of high importance in the offshore industry. In-service assessment of loads in the mooring lines is however very challenging. Direct monitoring of mooring line loads through load cells or inclinometers requires subsea installation work and continuous data transmission. Other solutions based on GPS and motion monitoring have been presented as solutions to overcome these limitations [1]. Monitoring solutions based on GPS and motion data provide good practical benefits, because monitoring can be conducted from accessible area. The procedure relies on accurate numerical models to model the relation between global motions and response of the mooring system. In this paper, validation of this monitoring approach for a single unit will be presented. The unit under consideration is a turret-moored unit operating in Australia. In-service measurements of motions, GPS and line tensions are available. A numerical time-domain model of the mooring system was created. This model was used to simulate mooring line tensions due to measured FPSO motions. Using the measured unit response avoids the uncertainty resulting from a prediction of the hydrodynamic response. Measurements from load cells in various mooring lines are available. These measurements were compared against the results obtained from the simulations for validation of the approach. Three different periods, comprising a total of five weeks of data, were examined in more detail. Two periods are mild weather conditions with different dominant wave directions. The third period features heavy weather conditions. In this paper, the data set and numerical model are presented. A comparison between the measured and numerically calculated mooring line forces will be presented. Differences between the calculated and measured forces are examined. This validation study has shown that in-service monitoring of mooring line loads through GPS and motion data provides a new opportunity for mooring integrity assessment with reduced monitoring system complexity.

Studies on Salt and Water Balance in Caddis Larvae (Trichoptera)

1961 ◽  
Vol 38 (3) ◽  
pp. 521-530 ◽  
Author(s):  
D. W. SUTCLIFFE
Keyword(s):  
Sea Water ◽  
Salt Water ◽  
Chloride Concentration ◽  
Malpighian Tubule ◽  
Sodium Concentration ◽  
Fluid Composition ◽  
Chloride Level ◽  
Highly Sensitive ◽  
Water Media ◽  
Salt And Water Balance

1. Survival and regulation in sea-water media was studied in the freshwater caddises Limnephilus stigma and Anabolia nervosa. 2. The majority of larvae did not survive for more than a few days at external salt concentrations greater than about 6o mM./l. NaCl. 3. In sea-water media the haemolymph osmotic pressure increased to remain slightly hyper-osmotic to the medium. The haemolymph sodium level also increased to remain slightly hypertonic to the medium, but the chloride level was maintained hypotonic until just prior to death of the larvae. 4. When the haemolymph chloride concentration was raised above the normal level, the Malpighian tubule-rectal system elaborated fluid in which the chloride concentration was hypertonic to the haemolymph. The system is highly sensitive to changes in the haemolymph chloride level. 5. The regulation of body-fluid composition in the freshwater caddises is compared with that found previously in the euryhaline larvae of Limnephilus affinis. It is suggested that the maintenance of a low haemolymph sodium concentration in L. affinis larvae is an important part of the adaptation for survival in salt water.

scholarly journals Evaluation of coral reef carbonate production models at a global scale

2015 ◽  
Vol 12 (5) ◽  
pp. 1339-1356 ◽  
Author(s):  
N. S. Jones ◽  
A. Ridgwell ◽  
E. J. Hendy
Keyword(s):  
Coral Reef ◽  
Predictive Power ◽  
Numerical Models ◽  
Coral Cover ◽  
Light Availability ◽  
Global Scale ◽  
Data Set ◽  
Carbonate Production ◽  
Future Global Warming ◽  
Atmospheric Co2 Concentrations

Abstract. Calcification by coral reef communities is estimated to account for half of all carbonate produced in shallow water environments and more than 25% of the total carbonate buried in marine sediments globally. Production of calcium carbonate by coral reefs is therefore an important component of the global carbon cycle; it is also threatened by future global warming and other global change pressures. Numerical models of reefal carbonate production are needed for understanding how carbonate deposition responds to environmental conditions including atmospheric CO2 concentrations in the past and into the future. However, before any projections can be made, the basic test is to establish model skill in recreating present-day calcification rates. Here we evaluate four published model descriptions of reef carbonate production in terms of their predictive power, at both local and global scales. We also compile available global data on reef calcification to produce an independent observation-based data set for the model evaluation of carbonate budget outputs. The four calcification models are based on functions sensitive to combinations of light availability, aragonite saturation (Ωa) and temperature and were implemented within a specifically developed global framework, the Global Reef Accretion Model (GRAM). No model was able to reproduce independent rate estimates of whole-reef calcification, and the output from the temperature-only based approach was the only model to significantly correlate with coral-calcification rate observations. The absence of any predictive power for whole reef systems, even when consistent at the scale of individual corals, points to the overriding importance of coral cover estimates in the calculations. Our work highlights the need for an ecosystem modelling approach, accounting for population dynamics in terms of mortality and recruitment and hence calcifier abundance, in estimating global reef carbonate budgets. In addition, validation of reef carbonate budgets is severely hampered by limited and inconsistent methodology in reef-scale observations.

Characteristics of variably saturated granular bentonite after long-term storage at near-field relevant temperatures

Clay Minerals ◽  
2013 ◽  
Vol 48 (2) ◽  
pp. 343-361 ◽  
Author(s):  
M. Valter ◽  
M. Plötze
Keyword(s):  
Physicochemical Properties ◽  
Cation Exchange ◽  
Surface Area ◽  
Cation Exchange Capacity ◽  
Elevated Temperatures ◽  
Near Field ◽  
Exchange Capacity ◽  
Hydraulic Permeability ◽  
Cation Composition ◽  
Retention Capacity

AbstractBentonite is a potential material for use in the engineered barrier of radioactive waste repositories because of its low hydraulic permeability, self-sealing capability and retention capacity. It is expected that bentonite would react at the elevated temperatures accompanying the radioactive decay in the nuclear waste. The presented study was started in order to improve understanding of the coupled influence of temperature and (pore) water on the physicochemical and mineralogical properties of bentonite during thermal treatment under near-field relevant conditions. Granular Na-bentonite MX-80 was differently saturated (Sr = 1–0.05) and stored at different temperatures (50–150°C) in a closed system. Upon dismantling after different periods of time (3 to 18 months), mineralogical characteristics, cation exchange capacity and content of leachable cations, as well as physicochemical properties such as surface area and water adsorption were investigated.The results showed a high mineralogical stability. A slight conversion from the sodium to an earth alkali form of the bentonite was observed. However, considerable changes in the physicochemical properties of the bentonite were observed, particularly by treatment above the critical temperature of 120°C. The cation exchange capacity decreased during heating at 150°C by approximately. 10%. The specific surface area dropped by more than 50%. The water uptake capacity under free swelling conditions showed a slight tendency to lower values especially for samples heated for more than 12 months. The water vapour adsorption ability in contrast drops by 25% already within three months at T = 120°C. These changes are mostly related to the variations in the interlayer cation composition and to smectite aggregation processes. The observed alterations are rather subtle. However, temperatures ⩾ 120°C had a remarkable negative influence on different properties of MX-80.

A Numerical Simulation of Diffusion Experiment in Clay

2011 ◽  
Vol 322 ◽  
pp. 353-356
Author(s):  
Qing Chun Yang
Keyword(s):  
Numerical Simulation ◽  
Opalinus Clay ◽  
Isotropic Case ◽  
Diffusion Experiment ◽  
Deep Geological Repository ◽  
Transport Distance ◽  
Geological Repository ◽  
Geological Formation ◽  
Clay Formation ◽  
Anisotropic Case

Safety assessment of nuclear waste disposal in a deep geological repository requires understanding and quantifying radionuclide transport through the hosting geological formation. Determining diffusion parameters under real conditions is necessary for the performance assessment of a deep geological repository where high level wastes are placed for safety disposal. The in situ diffusion and retention (DR) experiments are designed to study the transport and retention properties of the Opalinus clay formation. In this paper, a scoping numerical simulation is performed in Opalinus Clay, The simulated results for all the traces illustrate that the maximum transport distance perpendicular to the bedding is larger in the isotropic case and those along the bedding is larger in the anisotropic case. Tracer depletion in the isotropic case is a little larger than in the anisotropic case. Deuterium and iodide can be detected in the other interval but strontium can’t. Since the length of injection interval is shorter than the transport distance, the anisotropy effect is clearly measurable. This numerical simulation of diffusion experiment aims at contributing to the optimum design of the experiment. The results of this experiment will provide additional insight into the role of diffusion anisotropy and sorption parameters for radionuclides in clays.

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