ERE3.2 | Radioactive waste repositories - Geosciences in the assessment of the long-term evolution of the geosphere
EDI
Radioactive waste repositories - Geosciences in the assessment of the long-term evolution of the geosphere
Convener: Vanessa Montoya | Co-conveners: Koen Beerten, Emiliano Stopelli, Theresa Hennig, Alwina HovingECSECS
Orals
| Tue, 16 Apr, 08:30–10:15 (CEST)
 
Room K2
Posters on site
| Attendance Tue, 16 Apr, 16:15–18:00 (CEST) | Display Tue, 16 Apr, 14:00–18:00
 
Hall X4
Orals |
Tue, 08:30
Tue, 16:15
Geoscience knowledge is essential to investigate safety requirements to construct a geological or surface disposal facility for radioactive waste in a specific selected site. Safety requirements include i) isolation of the nuclear waste from humans and the accessible biosphere, ii) containment by retention and retardation of contaminants, iii) limited water flow to the geo-engineered facility and iv) long-term geological stability of the site. For this reason, in this session, relevant topics included, but not limited, are:
• Constraints on kinetics of rock-water interactions under ambient/elevated temperature, through data-model comparison
• Constraints on flow and transport in host rocks, soils and surrounding aquifers through groundwater dating and tracing of natural study cases
This session is a forum for discussing challenging issues faced by geoscientists including:
• Thermo-hydro-mechanical-chemical (THMC) processes with implications on radionuclide migration and barrier performance
• Studies related to radionuclides migration through the multi-barrier system and radionuclide-rock interaction
• Water-rock interactions, flow and transport studies in hydro(geo)logical site characterization
• Characterization of natural and repository-induced bio-geo-chemical effects
• Linking hydrosphere, geosphere and biosphere in long-term evolution studies, including determining the rate of internal and external geodynamic processes and their effect on various sub-compartments of the disposal system (e.g., permafrost phenomenology, erosion, landscape evolution)
• Studies dealing with the performance of soil covers as (hydraulic) barriers for surface disposal through analyzing natural soil profiles in relevant pedological and hydro(geo)logical settings
• Development of new methodologies for site characterization and monitoring
• Climate change and its effect on groundwater flow and composition
• Data digitalization/management and parameter collection
Contributions on the above topics can include all aspects covering lab-scale experimentation, large-scale experiments in underground research laboratories, observation of natural analogues, physics- and data-driven modelling and code development. In this context, natural analogues are particular relevant in upscaling data (in space and time) obtained on laboratory and/or underground research laboratories (URL’s) and as such test future scenarios of long-term evolution.

Orals: Tue, 16 Apr | Room K2

08:30–08:35
Radionuclides migration
08:35–08:45
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EGU24-1916
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ERE3.2
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ECS
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Highlight
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On-site presentation
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Alexandra Duckstein, Solveig Pospiech, Raimon Tolosana-Delgado, and Vinzenz Brendler

In the event of radionuclides leaking from a deep geological repository for radioactive waste, they can reach the ecosphere through fluid migration pathways in the rock and aquifers. Retention mechanisms such as the sorption of radionuclides on the minerals along such pathways influence the migration patterns and are thus an essential part of the safety requirements. Consequently, determining the mineral composition and its spatial distribution of a crystalline host rock is an important task in the safety assessment for potential repositories.

In the SANGUR project (Systematic sensitivity analysis for mechanistic geochemical models using field data from crystalline rock) we aim to determine which parameters and their uncertainties are essential for developing models for the simulation of radionuclide retention in crystalline rock. Radionuclide retention is substantially affected by sorption processes on the mineral surfaces, described by distribution coefficients (Kd values). A subsequent sensitivity analysis will help to identify the most influential parameters.

In addition to the groundwater composition and the thermodynamic sorption data, the mineralogy and its heterogeneity of the host rock play an important role in establishing the model. For the sensitivity analysis, in turn, it is vital to be able to describe the uncertainties of the individual parameters in the model.

To quantify the uncertainties, we simulate crystalline rock based on MLA (Mineral Liberation Analyzer image) data using Multinary Random Fields geostatistics. The focus is not only on the mineral composition of the bulk rock as a function of number of mineral phases and variability in grain sizes, but above all on the determination of the mineral composition of the exposed surfaces with which the aqueous phase comes into contact and on which sorption processes will  thus preferentially take place.

Besides the question of how detailed the rock must be modeled in order to adequately capture the heterogeneities, the question of the model scale or the size of the representative volume element is also addressed.

In addition to the discussion of the methodology and the results of the host rock simulations, we show the results of an initial study that enables us to determine what size the representative volume element should have in order to best describe the heterogeneities of the host rock for the subsequent calculation of the Kd values and their uncertainties.

How to cite: Duckstein, A., Pospiech, S., Tolosana-Delgado, R., and Brendler, V.: Radionuclide sorption in the far field: Geostatistical simulation of crystalline rock to assess uncertainties due to heterogeneities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1916, https://doi.org/10.5194/egusphere-egu24-1916, 2024.

08:45–08:55
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EGU24-11390
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ERE3.2
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ECS
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Highlight
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On-site presentation
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Nikolai Trofimov, Inna Kurganskaya, and Andreas Luttge

Barite (BaSO4) is a common rock-forming mineral, controlling barium behavior in Earth’s crust and marine water. This mineral can incorporate Sr and Ra into the crystal lattice by forming binary and ternary solid solutions. It makes barite a promising material for use in nuclear storages e.g., for nuclear waste containers. The achievement of high levels of safety in modern nuclear waste deposits requires studies on container’s material-water interaction. The data on solid-liquid interface reactions can be obtained by both experimental and computational methods. The most widespread experimental methods for studying surface reaction kinetics are Atomic Force Microscopy (Putnis, 1995; Bosbach, 1998; Risthaus, 2001; Kuwahara, 2011) and Vertical Scanning Interferometry (Luttge, 2010). However, these methods do not provide information on reaction mechanisms at the molecular scale. Approaches such as Density Functional Theory and Molecular Dynamics give detailed information of the reaction mechanisms at the nano-scale but are limited by the computational costs, system size, and reactions time period (Kurganskaya et al., 2022). Kinetic Monte Carlo is a stochastic approach, which can be successfully used as a connecting link between molecular and macroscopic scales, incorporating both experimental (AFM, VSI) and computational (DFT, MD) data. The KMC model of pure barite dissolution in water was developed by Kurganskaya et al., 2022. We present a new Kinetic Monte Carlo model of mineral-water dissolution in (Ba,Sr,Ra)SO4 system and discuss the general approaches for KMC models parameterization, based on a crystal chemistry of studied material.

Putnis, A., Junta-Rosso, J. L., & Hochella Jr, M. F. (1995). Dissolution of barite by a chelating ligand: An atomic force microscopy study. Geochimica et Cosmochimica Acta59(22), 4623-4632.

Bosbach, D., Hall, C., & Putnis, A. (1998). Mineral precipitation and dissolution in aqueous solution: in-situ microscopic observations on barite (001) with atomic force microscopy. Chemical Geology151(1-4), 143-160.

Risthaus, P., Bosbach, D., Becker, U., & Putnis, A. (2001). Barite scale formation and dissolution at high ionic strength studied with atomic force microscopy. Colloids and Surfaces A: Physicochemical and Engineering Aspects191(3), 201-214.

Kuwahara, Y. (2011). In situ Atomic Force Microscopy study of dissolution of the barite (0 0 1) surface in water at 30° C. Geochimica et Cosmochimica Acta75(1), 41-51.

Luttge, A., & Arvidson, R. S. (2010). Reactions at surfaces: a new approach integrating interferometry and kinetic simulations. Journal of the American Ceramic Society93(11), 3519-3530.

Kurganskaya, I., Rohlfs, R. D., & Luttge, A. (2023). Multi-scale modeling of crystal-fluid interactions: state-of-the-art, challenges and prospects.

Kurganskaya, I., Trofimov, N., & Luttge, A. (2022). A Kinetic Monte Carlo Approach to Model Barite Dissolution: The Role of Reactive Site Geometry. Minerals12(5), 639.

How to cite: Trofimov, N., Kurganskaya, I., and Luttge, A.: Kinetic Monte Carlo as a bridge between nano- and macroscales: a case study on dissolution of (Ba,Sr,Ra)SO4 solid solution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11390, https://doi.org/10.5194/egusphere-egu24-11390, 2024.

08:55–09:05
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EGU24-11632
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ERE3.2
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Highlight
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On-site presentation
Marco De Lucia, Max Lübke, and Bettina Schnor

The computational burden associated with coupled reactive transport simulations limits their application coarse models and thus to oversimplified geological and geochemical features, with obvious repercussions on uncertainty and safety assessment of nuclear waste disposal facilities. Techniques from approximated computing can however be leveraged to accelerate simulations of large-scale, heterogeneous domains. These include both surrogate models based on machine learning and artificial intelligence (ML/AI) to replace more costly numerical geochemical simulators, and algorithmic improvements such as interpolation from previously computed geochemical simulations stored and indexed in efficient data structures such as  Distributed Hash Tables during coupled simulations. In this contribution we demonstrate recent advancements in physics-based geochemical surrogates achieved within the ML-Benchmark initiative from the DONUT/EURAD project for Uranium diffusion in clay subject to exchange and sorption. Furthermore, the algorithm implemented in the reactive transport simulator POET [1] based on automatic clustering of multivariate data and subsequent interpolation enables the simulation of large-scale, heterogeneous reactive transport scenarios on uniform grids of magnitude of million grid elements at reduced computational costs.


[1] Marco De Lucia, Michael Kühn, Alexander Lindemann, Max Lübke, and Bettina Schnor, 2021: POET (v0.1): speedup of many-core parallel
reactive transport simulations with fast DHT lookups, Geoscientific Model Development, 14, 7391--7409. https://doi.org/10.5194/gmd-14-7391-2021

How to cite: De Lucia, M., Lübke, M., and Schnor, B.: 2D simulations of Uranium diffusion in clay: geochemical surrogate models and accelerated coupled reactive transport simulations with POET, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11632, https://doi.org/10.5194/egusphere-egu24-11632, 2024.

09:05–09:15
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EGU24-13990
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ERE3.2
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ECS
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On-site presentation
Qingyin Xia, Yuqing Niu, Longcheng Liu, Zhean Zhang, and Tingting Xie

Clay and clay rocks are being considered as possible barriers for nuclear waste disposal worldwide, due to their high adsorption capacity and limited hydraulic conductivity. Moreover, clay minerals have been regarded as one of the major Fe-containing phases in the Earth’s crust due to their ubiquitous occurrences in soil and sediments.  Hence, a solid understanding of uranium interactions with Fe(III)-bearing clay minerals is needed for the optimal design and long-term stewardship of uranium waste disposal. Besides clay minerals, metal-chelating ligands were found at appreciable concentrations in certain uranium-contaminated sites due to their prevalent use as decontaminant (e.g., complexing) agents in radioactive waste streams, which ultimately impacted the redox kinetics of U in proximity.

Herein, we report a combined effect of Fe(III)-rich nontronite (NAu-2) and environmentally prevalent organic ligands on re-oxidation of biogenic UO2 at circumneutral pH. After 30 d incubation, structural Fe(III) in NAu-2 oxidized 45.50% UO2 with an initial rate of 2.68*10-3 mol*m-2*d-1. The addition of citrate and EDTA greatly promoted the oxidative dissolution of UO2 by structural Fe(III) in NAu-2, primarily through the formation of aqueous ligand-U(IV) complexes. In contrast, a model siderophore, DFOB, partially inhibited UO2 oxidation due to the formation of a stable DFOB-Fe3+ complex. The resulting U(VI) species intercalated into the NAu-2 interlayer, driving UO2 dissolution by keeping dissolved U(VI) concentrations low. Our results highlight the importance of organic ligands on the oxidative dissolution of U(IV) minerals by Fe(III)-bearing clay minerals and have important implications for the design of nuclear waste storage and remediation strategies, especially in clay- and organic-rich environments.

How to cite: Xia, Q., Niu, Y., Liu, L., Zhang, Z., and Xie, T.: The roles of clay minerals and/or organic ligands in the mobility of uranium: an insight for geological disposal of radioactive waste, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13990, https://doi.org/10.5194/egusphere-egu24-13990, 2024.

Rock fractures
09:15–09:25
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EGU24-10758
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ERE3.2
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ECS
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On-site presentation
Mostafa Mollaali, Renchao Lu, Keita Yoshioka, Wenqing Wang, Vanessa Montoya, and Olaf Kolditz

We present a fully coupled chemo-hydro-mechanical variational phase field model for simulating fracture initiation and propagation, including chemical reactions in cementitious systems. Using a staggered approach, we coupled three subprocesses: (i) fluid flow in porous media, (ii) reactive transport, and (iii) mechanical deformation of fractured porous media using a variational phase field. The geochemical package PHREEQC was coupled in an operator-splitting approach with a finite element transport solver to calculate chemical reactions in thermodynamic equilibrium (dissolution or precipitation), considering changes in porosity. Mechanical deformation and fluid flow were coupled using the fixed-stress splitting approach. For chemical damage, we introduced a variable to a constitutive relation representing a degree of chemical damage ranging from zero (intact) to one (damaged material). This chemical damage variable represents changes in porosity caused by chemical reactions independently from the phase field variable that represents the mechanical damage.

Additionally, as effective diffusion and hydraulic conductivity increase in the presence of fracture and changes in porosity, the phase field variable and chemical damage should impact the hydraulic conductivity and the diffusion coefficient. We conducted different benchmarks to demonstrate the model's capabilities and properties in capturing fracture initiation and propagation due to chemical reactions. The proposed model was implemented in the open-source finite element framework OpenGeoSys. 

How to cite: Mollaali, M., Lu, R., Yoshioka, K., Wang, W., Montoya, V., and Kolditz, O.: Chemo-Hydro-Mechanical variational phase-field fracture model , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10758, https://doi.org/10.5194/egusphere-egu24-10758, 2024.

09:25–09:35
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EGU24-11766
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ERE3.2
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On-site presentation
Andrew Frampton

There is a need for improved understanding of flow channelling and solute transport in fractured crystalline rock in the context of safety analysis of geological repositories for spent nuclear fuel. Numerical discrete fracture network (DFN) models of sparsely fracture rock often employ an assumption of effectively homogeneous properties at the scale of individual fractures. However, real-world fractures have rough surfaces which translates to internal variability in aperture and permeability which can impact transport properties. Although it is known that internal variability controls flow channelling at the scale of single fractures, there is a lack of understanding of effects at the bedrock scale of multiple connected fractures forming networks. Therefore, it is relevant to study internal fracture variability in DFN models to better understand potential impacts on flow and transport.

In this contribution, flow channelling and solute transport in three-dimensional fracture networks with internal variability in permeability is investigated using a numerical DFN flow model with a stochastic Lagrangian transport framework. The fracture network properties are obtained from field measurements and data of fractured rock from the Forsmark site in Sweden, which is a planned location for the construction of the spent nuclear fuel repository. Different assumptions for describing the correlation length of the textures used for internal variability of fracture permeability are considered. Multiple realisations are generated and it is shown that cases with strong correlation length can lead to reduced travel times and reduced solute retention when compared to cases assuming homogenous fractures. The changes observed occur only for a small fraction of early arrivals, whereas bulk mass is essentially unaltered, and late mass breakthrough with strong retention is generally enhanced. Cases with weak correlation lengths generally have minor impacts. Thereby key thresholds for cases where flow channelling is controlled by internal fracture variability versus network scale connectivity are discussed, and a need to understand and evaluate correlation structures for real-world fractures is highlighted.

How to cite: Frampton, A.: Effects of internal fracture variability on flow channelling in discrete fracture network models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11766, https://doi.org/10.5194/egusphere-egu24-11766, 2024.

09:35–09:45
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EGU24-18157
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ERE3.2
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ECS
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On-site presentation
Michael Kröhn and Klaus-Peter Kröhn

In the German site selection process for a nuclear waste repository, crystalline rock is one of three different types of host rock that are currently considered. As contact of groundwater with the waste canisters poses one of the main threats to such a repository, knowledge about groundwater flow in the general area is essential for a safety assessment. By law, the safety of a nuclear waste repository in Germany must be ensured for at least one million years. During this time, several ice ages are very likely to occur. They are expected to cause permafrost conditions in the underground at any conceivable location for a repository and are to be considered in the safety assessment as they are accompanied by considerable changes in groundwater flow due to freezing.

Freezing of water in a classic porous medium does not result in an instantaneous phase change of the whole pore water, though. Within a certain temperature range, an increasing volume of ice builds up in the pore space with falling temperatures. The referring Soil Freezing Characteristic Curve (SFCC) relates the degree of water/ice saturation with temperature thereby providing a key parameter for the temperature-dependent relative permeability. While these constitutive relations have already been investigated for classic porous media, hardly any information is available yet for fracture flow in crystalline rock. A new methodology has thus been developed for measuring the temperature-dependent relative permeability in fractures.

Based on a digital representation, a transparent fracture replica with a size of 7 by 10cm has been 3d printed. As groundwater flow in granite mainly occurs within the fractures, the influence of the rock matrix on such processes is neglected by the new method. To detect the formation of ice inside the fracture replica, a LED light source was placed underneath the fracture replica and freezing as well as melting processes were observed by a camera positioned above the fracture. The whole experimental setup was placed inside a climate chamber to test the influence of different temperatures. Before the tests, all components were tempered for at least 3 days before the system got completely flooded. The distinction between water as well as ice who are both transparent in their natural state was rendered possible by using a 0,05% methylene-blue solution. In a liquid state it is dark blue while being transparent in solid state. Pretesting ensured that the added methylene-blue has only a negligible effect on the freezing behavior. In parallel to observing visually the freezing and thawing in the fracture, the related effective permeability was determined by measuring the outflow rate at a constant inflow pressure.  

The obtained images were segmented using Matlab for evaluating the ratio between ice and liquid water. In combination with the performed flow tests, the relation between relative permeability and ice content has been determined for the printed fracture replica. Further tests with variations of the replica are envisioned.

How to cite: Kröhn, M. and Kröhn, K.-P.: Visual observation of freezing and thawing processes in 3d printed fracture replicas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18157, https://doi.org/10.5194/egusphere-egu24-18157, 2024.

Climate change, glaciation and subglacial erosion and permafrost formation
09:45–09:55
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EGU24-13289
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ERE3.2
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Highlight
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On-site presentation
Angela Landgraf, Michael Schnellmann, Kristin Vogel, Wolfgang Betz, Daniel Straub, Wolfgang Schwanghart, J Ramon Arrowsmith, Simon Mudd, Emma Graf, Andreas Ludwig, Florian Kober, Gaudenz Deplazes, Urs Fischer, Jens Becker, Fabian Maier, and Frank Scherbaum

The safety assessment of radioactive waste repositories requires scenarios and forecasts of the erosional, climatic, and tectonic future evolution. One of the major challenges in the assessment of long-term landscape evolution for safety is that the relevant processes, models and model parameters are subject to a range of significant uncertainties. Assessments should provide the full range of conceivable developments using the best available scientific knowledge. Here, we present an assessment framework for future erosion with a rigorous uncertainty management. The approach anticipates erosion from fluvial, hillslope, and glacial processes over a timescale of 105-106 years. Uncertainties are addressed in a hybrid way, using probabilistic methods in combination with a scenario approach, whereby the chosen scenarios cover a wide range of possibilities. A protocol was followed to derive model parameter uncertainties that respect individual estimates of experts. The entire process is accompanied by a sensitivity analysis. We used the workflow to assess erosion in Northern Switzerland over the next million years. The results serve as input to site a deep geological repository for nuclear waste in Switzerland and to demonstrate its long-term safety.

How to cite: Landgraf, A., Schnellmann, M., Vogel, K., Betz, W., Straub, D., Schwanghart, W., Arrowsmith, J. R., Mudd, S., Graf, E., Ludwig, A., Kober, F., Deplazes, G., Fischer, U., Becker, J., Maier, F., and Scherbaum, F.: Assessing the effects of long-term landscape evolution on the overburden of deep repository sites: application to northern Switzerland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13289, https://doi.org/10.5194/egusphere-egu24-13289, 2024.

09:55–10:05
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EGU24-3146
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ERE3.2
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Highlight
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On-site presentation
Jörg Lang, Anke Bebiolka, Sonja Breuer, Andrea Hampel, and Vera Noack

The safety of repositories for high-level radioactive waste has to be assessed for very long time periods (e.g., 1 Ma by German regulations), which implies that the impact of potential future cold stages and glaciations on the geological barrier of a repository needs to be considered. The largest impact may occur if a repository site is transgressed by an ice sheet or at least in the immediate proximity of an ice margin. However, also repository sites outside the maximum ice-sheet extent may be affected. Examples of relevant processes with potentially huge impacts include glacigenic erosion and ice-load induced deformation of rocks. Erosion by glaciers and meltwater is capable of mobilising and redistributing substantial amounts of rock and sediment. Overdeepened basins and (tunnel) valleys may attain depths of more than 500 m, which is within the depth range considered for repositories. Subglacial overdeepenings form independently of any regional base level as their formation relates to pressurised meltwater that effectively removes sediment.

Ice-load induced deformation of rocks includes glacial isostatic adjustment (GIA), deformation of salt structures and glacitectonics. The weight of an ice sheet triggers long-wavelength glacial isostatic adjustments, which strongly modify the regional stress field. Such changes of the stress field may cause the activation or shutdown of faults and affects areas beyond the ice margin. More locally, ice-sheet loading may trigger the deformation of salt structures due to the viscous behaviour of salt rocks. Glacitectonic deformation affects near surface rocks and includes the formation of glacitectonic shear zones, folds and faults. Movements of rock masses induced by ice loading, particularly along faults, have the potential of creating fluid pathways. Additionally, glacitectonic thrusting can relocate coherent rock masses from depths of up to 350 m.

Key to assessing the potential impact of future glaciations is the thorough understanding of the processes during past glaciations, which serve as analogues for the future. The effects of past glaciations can be analysed to reconstruct processes and allow the quantification of past extreme scenarios (e.g., depth of erosion). Numerical models are another important tool and allow the quantification and evaluation of controlling factors and the testing of extreme values (e.g., thickness of ice sheets). Ideally, both approaches should be combined to assess the potential impact of a glaciation on the geological barrier of a repository.

Examples will be presented from current projects incorporating reconstructions of Pleistocene processes into long-term safety assessments. The first case study is on the maximum depth of Pleistocene erosion in northern Germany (Breuer et al. 2023). Based on the mapped depth zones, the potential for erosion can be assessed. The second case study is a numerical simulation of the response of salt structures to ice-sheet loading (Lang & Hampel 2023), which provides new insights into the relevant controlling factors of ice-salt interactions.

 

References

Breuer et al. (2023) E&G Quat. Sci. J., 72, 113-125, DOI: https://doi.org/10.5194/egqsj-72-113-2023

Lang & Hampel (2023) Intern. J. Earth Sci. 112, 1133-1155, DOI: https://doi.org/10.1007/s00531-023-02295-5

How to cite: Lang, J., Bebiolka, A., Breuer, S., Hampel, A., and Noack, V.: Assessing the impact of potential future glaciations on the long-term safety of radioactive waste repositories: relevant processes and examples from current studies, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3146, https://doi.org/10.5194/egusphere-egu24-3146, 2024.

10:05–10:15
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EGU24-16907
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ERE3.2
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On-site presentation
Johan Liakka, Jens-Ove Näslund, Rémi Vachon, and Dan J Lunt

In many regions considered for deep geological repositories (DGR) to contain nuclear waste, there will be repeated glaciations throughout periods pertinent to their long-term safety (up to 1 million years; Ma). Ice sheets can influence the containment of radionuclides through various mechanisms. For example, when the margin of an ice sheet is situated in close proximity to the DGR, groundwater flow may increase, potentially leading to enhanced erosion and corrosion of the technical barriers within the DGR. Furthermore, the temporal extent of glaciations at the DGR site impacts groundwater chemistry, such as salinity and oxygen content, as well as the magnitude of glacial isostatic adjustment and surface bedrock denudation over the ensuing 1 Ma. Consequently, evaluations of long-term DGR safety must account for uncertainties related to ice-sheet variability at the DGR site throughout the next 1 Ma, specifically addressing the frequency of glaciations (nglac) and the total duration of ice-sheet coverage (tglac). Additionally, assessments should consider the potential for ice-marginal stillstands, denoting temporary halts in the advancement and/or retreat of the ice-sheet margin over the DGR site.

The utilization of coupled ice sheet-climate models for constraining uncertainties in nglac and tglac over the next 1 Ma is not feasible due to the long timescales involved and substantial computational requirements. To assess future ice-sheet variability, we propose a simplified methodology that uses (i) reconstructions of historical ice sheets, (ii) records of past global ice-volume fluctuations, and (iii) simulations of future global ice-volume changes. These simulations are conducted using a simple multi-step climate model, which is driven by changes in insolation and radiative forcing due to atmospheric greenhouse gases.

Utilizing the proposed methodology on the Swedish site chosen for nuclear waste disposal (Forsmark) suggests that the onset of the first glaciation at the site is projected not to take place within the coming 100,000 years (100 ka), irrespective of human-induced greenhouse-gas emissions. Following the initial glacial event at Forsmark, the frequency and duration of subsequent glaciations will likely be similar to those observed in the late Quaternary (last 800 ka). Taking into consideration identified model and scenario uncertainties, the total glaciation duration (tglac) at Forsmark may either decrease by a factor of five or increase by a factor of two in comparison to the average conditions of the late Quaternary. In contrast to tglac, the number of glaciations (nglac) at Forsmark is found to be largely insensitive to the evaluated uncertainties.

The potential for ice-margin stillstands within the next 1 Ma is assessed through theoretical considerations complemented by simulations with ice-sheet model simulations. Initial findings indicate that stillstands will be brief, lasting less than 1000 years under nearly all examined scenarios. This observation aligns with historical records of stillstands during the last deglaciation. The occurrence of stillstands modestly exceeding 1000 years can only occur if a glacial maximum is promptly followed by a millennial-scale cooling event.

How to cite: Liakka, J., Näslund, J.-O., Vachon, R., and Lunt, D. J.: Assessing Ice-Sheet Variability for Post-Closure Safety of Deep Geological Repositories, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16907, https://doi.org/10.5194/egusphere-egu24-16907, 2024.

Posters on site: Tue, 16 Apr, 16:15–18:00 | Hall X4

Display time: Tue, 16 Apr 14:00–Tue, 16 Apr 18:00
X4.143
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EGU24-3991
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ERE3.2
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ECS
Theresa Hennig, Sina Grossmann, and Vinzenz Brendler

Smectite-rich natural clays, usually referred to as bentonite, are used as backfill material in disposal concepts for highly-radioactive wastes. The main component of bentonite is montmorillonite, characterised by a high cation exchange capacity resulting from isomorphous substitution and swelling due to the incorporation of water molecules between the stacked clay platelets, the interlayer. These properties render bentonite an ideally suited barrier material for cationic radionuclides. Caesium is such a radionuclide that is relevant in the context of nuclear waste disposal since it is highly soluble and can be incorporated in organisms.

Migration of caesium in MX-80 bentonite (Na-montmorillonite) was investigated for different dry bulk densities (1.3, 1.6 and 1.9 g/cm³) in long-term through-diffusion experiments running for up to 600 days. Diffusion experiments of tritiated water (HTO, non-sorbing) provided the transport accessible porosities. Batch sorption experiments at varying caesium concentrations should test the transferability between dispersed and compacted systems by means of the distribution coefficient Kd (m³/kg). The synthetic pore water compositions were calculated as a function of the dry bulk density. Caesium and HTO are expected to migrate via molecular diffusion through the compacted bentonite sample. Therefore, a one-dimensional numerical model was applied to determine the transport parameters, effective diffusion coefficient De (m²/s) and rock capacity factor α (-), from the temporal evolution of the diffusive flux and the accumulated activity.

In the dispersed systems, measured Kd values increase with decreasing caesium concentration and dry bulk density. The linear sorption isotherm indicates that sorption mainly occurred via cation exchange, predominantly with ions from the interlayer. Accordingly, the higher the cation concentration in the contacting pore water, less caesium is exchanged due to competing effects. At low concentrations (<10-6 mol/L), however, the measured sorbed caesium concentrations do not match exactly with the isotherm. This can be attributed to impurities in form of illite-smectite mixed layers. With increasing caesium concentration, measured Kd decreases due to saturation of the high affinity sites at the illite surfaces. Kd values differ by a factor of up to ten between batch and compacted systems. With compaction, the amount of water in the interlayer decreases. This, in turn, affects the space and ability to hydrate sodium so that it is exchanged with the less hydrated caesium from the bulk solution. Accordingly, Kd values are not transferable due to thermodynamic changes of the exchange process with compaction. Consequently, caesium sorption depends on the ionic strength, the compaction and on the caesium concentration.

With increasing bulk density, the apparent diffusion coefficients of caesium decrease by a factor of ten. In general, diffusion of caesium was twice as high as that of HTO. This can be attributed to an additional transport pathway in the interlayer, which is not accessible for neutral species. For the transient phase, there was an offset between simulations and experiments, what might be explained by higher temperatures at the beginning of the experiments. Simulated and experimental steady-state phases are in line. With compaction, sorption increases, and thus diffusivity decreases.

How to cite: Hennig, T., Grossmann, S., and Brendler, V.: Diffusion and sorption of caesium depend on the dry bulk density of bentonite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3991, https://doi.org/10.5194/egusphere-egu24-3991, 2024.

X4.144
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EGU24-15090
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ERE3.2
Aaron Peche, Tuong Vi Tran, and Sven Altfelder

The release and migration of radionuclides towards the biosphere from underground waste repositories may pose a threat to the environment and humans. Therefore, the understanding of transport processes of radionuclides in the subsurface is crucial in order to predict the arrival in the near-surface environment for effectively mitigating and managing associated risk. Processes controlling radionuclide transport may be advection, dispersion, diffusion, sorption and decay, among others.

In the context and typical locations of existing waste repositories and test sites, diffusion-dominated transport occurs. Typically, local permeabilities and flow velocities are so small that advection and dispersion would only become significant at very large timescales. The processes of diffusion, sorption (possibly modulated by pressure and temperature) and decay may often be crucial for a) predicting the gradual release and movement of contaminants from the repository into the surrounding geological formations and b) in the geological barrier itself as part of safety analyses. Therefore, understanding of barrier-specific diffusion processes is essential for assessing long-term containment and designing effective concepts to ensure reliable isolation of radionuclides over a time period long enough for their decay to safe levels and to avoid potential environmental risks associated with the disposal of radioactive waste.

In the present desktop study, we calculate diffusion-dominated transport of specific radionuclides (Tritium, Technetium, Neptunium a.o.) for various host rocks (tuff a.o.). We calculate radionuclide breakthrough curves and timescales using the 1D analytical model by Lapidus & Amundson (1952), extended for decay in Bear (1972). In order to validate transport parameters for specific radionuclides in specific rock, we analytically try to reproduce physical radionuclide diffusion experiments. Subsequently, we use the validated transport parameters to predict timescales of diffusion-dominated transport.

References:

Bear, J., 1972. Dynamics of Fluids in Porous Media. American Elsevier, New York.

Lapidus, L., & Amundson, N. R. (1952). Mathematics of adsorption in beds. VI. The effect of longitudinal diffusion in ion exchange and chromatographic columns. The Journal of Physical Chemistry, 56(8), 984-988.

How to cite: Peche, A., Tran, T. V., and Altfelder, S.: Timescales of diffusion-dominated radionuclide migration – an evaluation of selected existing nuclear waste repository sites and test sites , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15090, https://doi.org/10.5194/egusphere-egu24-15090, 2024.

X4.145
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EGU24-3471
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ERE3.2
Solveig Pospiech, Frank Bok, Mostafa Abdelhafiz, Alexandra Duckstein, Elmar Plischke, and Vinzenz Brendler

The secure disposal of nuclear waste is of high societal concern, necessitating the development of deep geological repositories as a reliable solution. A key aspect of repository safety lies in understanding the far field, particularly the host rock, to predict the long-term behavior and migration of radionuclides within the geological environment from the deposit up to the ecosphere. This study addresses the specific challenges associated with crystalline host rocks.

Crystalline host rocks could be on the one hand of granitic composition and texture, but the term is also used for host rocks of metamorphic origin. While inside a large granitic intrusion there is little petrological variation expected, metamorphic rocks or the intrusion rim can exhibit complex structures in terms of structural geology as well as mineral composition, especially along potential fluid migration pathways. Consequently, this leads to a multitude of possible rock-composition/fluid-composition interactions and thus significantly affects the retention potential of radionuclides as opposed to the simplified model of an isotropic, uniform granite. The results of the study will allow to determine which components of the host rock are important to be included in geostatistical models which in turn serve as basis to estimate uncertainties of reactive transport through crystalline rocks.

Our study involves the development of Python code to feed chemical modelling software like PHREEQC or Geochemist’s Workbench© with varying mineral compositions and chemical conditions of the aqueous phase, following a specific Quasi-Monte-Carlo sampling scheme. The application of compositional data analysis principles is essential to guarantee a meaningful sampling of constraint concentration data, such as mineralogical rock compositions or element concentrations in aqueous phases. Given that compositional data sum to a fixed total, each mineral content becomes a dependent variable in relation to the other contents. Recognizing and accounting for these interdependencies is crucial to ensuring the integrity of the sampling. The chemical modelling software relies on Surface Complexation Models (SCM) for each mineral phase to calculate the distribution coefficient (Kd-value) for the radionuclide (here: uranium) in the respective setting. Furthermore, a global sensitivity analysis is employed to investigate the complex interactions between mineralogical variations and radionuclide behavior. In this study, two techniques are employed namely, High-Dimensional Model Representation (HDMR) and Cumulative Sum of Univariate Nonlinear Regression (CUSUNORO) plots. The application of HDMR allows for a detailed investigation of high-dimensional parameter spaces, while CUSUNORO plots provide a visual representation of cumulative sensitivity effects.

This study presents a complete workflow of modelling how petrological variations in crystalline host rocks, including both granitic and metamorphic compositions, affects radionuclide retention. This approach advances the understanding of nuclear waste disposal and provides valuable tools for assessing the retention potential of radionuclides in diverse geological settings.

How to cite: Pospiech, S., Bok, F., Abdelhafiz, M., Duckstein, A., Plischke, E., and Brendler, V.: Understanding Geological Key Factors for Radionuclide Retention: Insights from Sensitivity Analysis on Varied Crystalline Host Rock Compositions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3471, https://doi.org/10.5194/egusphere-egu24-3471, 2024.

X4.146
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EGU24-19338
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ERE3.2
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ECS
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Highlight
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Sebastian Schramm, Ferry Schiperski, Mathias Hübschmann, Frank Horna, and Traugott Scheytt

Geochemical background values are commonly used for the authorization of remediation measures. However, in the case of the former Königstein uranium ore mine, located in Saxony (Germany), natural uranium concentrations in groundwater cannot be directly assessed, due to active mining activities. The Königstein uranium ore depositis located within the 4th aquifer and consists of the Oberhäslich Formation and 'Wurm'-Sandstone.

This study aimed at deriving natural uranium content using batch shake test, assuming chemical equilibrium with regard to the speciation of uranium in solution and the binding to the rock matrix. For that purpose, representative subsamples from core material were taken for batch experiments and geochemical analyses. As uranium solubility strongly dependents on the redox state, the pH value, and the hydrochemistry of the target fluid, experiments were performed under various conditions.

The rock samples were analyzed with respect to geochemical and mineralogical compositions, while uranium concentration in fluid samples was measured using inductively coupled plasma - mass spectrometry. Concentrations of major cations were analyzed using cation chromatography techniques. The PHREEQC software was used to analyses the species distribution of uranium under the hydrochemical conditions of the the unaffected inflowing water from the inflow area.

Results show, that the sandstones in the middle of the 4th aquifer consist mainly of SiO2 with more than 98 wt.-%. Two-layer clay minerals and iron oxides were identified in another sample with fractions more than 50 wt.-% kaolinite. Uranium was found in the anaerobic zone in one rock sample at 1820 ppm and once at only 25.6 ppm.

Equilibrium modeling revealed, that at a pH of 5.5 to 6 and under oxidizing conditions, uranium mainly occurs as UO22+, UO2OH+, and UO2CO3. It can therefore be expected that the uranium species present as cations will likely be adsorbed by the solid matrix. Initial shaking tests showed that combining reduced rock materials with oxidizing water led to excessive uranium fractionation into the fluid phase. Batch tests using deionised water showed uranium concentrations between 2 and 2.5 mg/l, contrasting expectation of natural uranium concentrations in the lower µg/l range.

How to cite: Schramm, S., Schiperski, F., Hübschmann, M., Horna, F., and Scheytt, T.: Geochemical composition of sandstone samples from drill cores of the former uranium ore mine Königstein (Saxony) and the determination of hydrochemical equilibrium concentrations of uranium by means of batch tests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19338, https://doi.org/10.5194/egusphere-egu24-19338, 2024.

X4.147
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EGU24-8225
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ERE3.2
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Highlight
Miroslav Honty, Alwina Hoving, Lander Frederickx, Jean-Marc Greneche, and Daniel Traber

The Boom Clay (BC) in Belgium and the Opalinus Clay (OPA) in Switzerland are studied as potential host rocks for radioactive waste disposal in the frame of national programmes. In the assessment of the long-term natural barrier evolution, redox capacity is an important physical-chemical parameter to consider as it may affect the speciation and migration behavior of the released radionuclides from the waste. In this respect, iron plays an important role in the electron transfer and thus may influence the speciation and transport of many redox sensitive radionuclides. The clay minerals, commonly present in these rocks, contain iron in the octahedral and tetrahedral sheets of their structure (e.g. illite, smectite, mixed layer illite-smectite (I-S) and chlorite). Despite their relatively high abundance in the sedimentary rocks, the electrochemical activity of iron within clay minerals may vary from as high as 100% in the case of pure smectite, through 41% in the mixed 70/30 layer I-S, 10% in illite and only 2% in chlorite. The electrochemical activities of non-clay iron-bearing minerals, is low in the case of pyrite (from 2 to 12%) and zero in the case of siderite.

In order to estimate the redox capacities of BC and OPA, Fe distribution, redox state and electrochemical activity were determined by a combination of quantitative XRD analysis (QXRD), XRF, phenanthroline, 57Fe Mössbauer spectroscopy and mediated electrochemical oxidation (MEO) and mediated electrochemical reduction (MER) measurements. In the bulk OPA clay samples, the Fe2+ states dominate over Fe3+ states, whereas Fe3+ states dominate over Fe2+ states in the studied bulk BC samples. In both cases, illite, I-S and smectite are the main Fe3+ carriers, while chlorite, pyrite and siderite are the main Fe2+ carriers. Fe distribution and the valence state are therefore controlled by the quantitative mineralogical composition in both rocks. The results of the MER and MEO measurements indicate that total electron transfer capacity (ETC) varies in the range between 45 and 64 µmol e-/g bulk OPA and between 160 and 181 µmol e-/g bulk BC. In most of the studied samples, the electron accepting capacity (EAC) is higher than the electron donating capacity (EDC). The measured EACs positively correlate with increasing Fe3+ contents, smectite content and cation exchange capacities. The correlation between measured EDCs and Fe2+ contents is less satisfactory, most likely due to overall low Fe2+ electrochemical activities reported for pure pyrite, chlorite and siderite. The quantitative mineralogical composition and available electrochemical data of the pure minerals were used to calculate the theoretical ETCs, EDCs and EACs of the studied OPA and BC samples. Despite relatively large uncertainties in the electrochemical activities in the EDC field, the correlation between theoretical and experimental EACs and ETCs is relatively good in both studied cases (R2 = 0.83 and 0.76, respectively for EAC and ETC in the case of OPA and R2=0.74 and 0.84 in the case of BC). The proposed mineral electrochemical model should be tested on larger data sets to verify its general applicability to other clay formations.

How to cite: Honty, M., Hoving, A., Frederickx, L., Greneche, J.-M., and Traber, D.: Towards a comprehensive model to estimate redox capacity of clay rocks studied as natural barriers for radioactive waste disposal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8225, https://doi.org/10.5194/egusphere-egu24-8225, 2024.

X4.148
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EGU24-1317
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ERE3.2
Anja Schleicher, Marie Bonitz, Theresa Hennig, Jessica Stammeier, David Jaeggi, and Michael Kühn

Opalinus Clay is the chosen host rock for the deep geological disposal of nuclear waste in Switzerland and is also being considered for this purpose in Germany. For the long-term integrity of the disposal site, temporally and spatially stable geochemical conditions are essential. Adjacent aquifers can induce changes into the system. It is therefore essential to investigate if and how the geochemistry and mineralogy of the sediments is influenced by the hydrogeology. Changes in the Opalinus Clay and the surrounding formations provide information about geochemical processes in the past and thus enable an assessment for the future.

In this context, a 58 m long borehole was drilled at the Swiss Rock Laboratory in Mont Terri. Drilling was conducted from the Opalinus Clay (Toarcian) through the entire Staffelegg Formation (Toarcian-Sinemurian), which contains two water-bearing sections. The groundwater, the members and their transitions were characterised with a variety of analytical methods.

Groundwater was found locally in the Beggingen (Gryphaea Limestone) and Rietheim (Posidonia Shale) members, depending on the presence of pathways in open fractures and with differences in their chemical composition. The groundwater in the Rietheim member is not directly connected to the surface, but seems to be continuously recharged by an adjacent aquifer. At the transition from the Gross Wolf to the Rietheim Member, pyrite increases and many trace elements are enriched. The Fe/Al paleoredox proxy and the enrichment of trace-metals like uranium reveal prevailing anoxic conditions in the sediment and groundwater. This is more indicative for a depositional than a mobilization feature. The influence of the groundwater can therefore be classified as limited due to its reducing conditions at this transition.

The aim is to establish a method for analytically distinguishing between features of deposition, diagenesis, alteration and mobilization. This will allow assessment of the long-term integrity of the Opalinus Clay as a host rock and the surrounding formations. The gained understanding of the hydrogeological influence on the geochemical conditions within a system is to be transferred to other potential repository sites.

How to cite: Schleicher, A., Bonitz, M., Hennig, T., Stammeier, J., Jaeggi, D., and Kühn, M.: Geochemical profiles in the hydrogeological system of the Opalinus Clay, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1317, https://doi.org/10.5194/egusphere-egu24-1317, 2024.

X4.149
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EGU24-7840
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ERE3.2
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ECS
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Jonas Suilmann, John Molson, and Thomas Graf

In the overburden of salt domes, salt is dissolved by groundwater, resulting in groundwater flow under highly variable water densities. Density-dependent flow is therefore important in assessing potential migration pathways for radionuclides accidentally released from high-level nuclear waste repositories located in salt domes. Groundwater life expectancy has been established as a safety indicator for radionuclide travel times and is therefore of particular interest.

The objective of this study is to numerically investigate and understand the effects of uncertain transport parameters on density-dependent flow above a salt dome. The effects of density-dependent flow and salt transport, along with the transport parameters on the groundwater life expectancy are investigated numerically using the FEM code Saltflow. Groundwater life expectancy can be directly simulated using an advection-dispersion equation. The life expectancy depends on the transport parameters in two ways, first via the flow velocities calculated in the density-dependent flow simulation which depend on the dispersion terms, and second directly for the calculation of the life expectancy. This suggests a strong and also highly non-linear dependence of life expectancy on the transport parameters.

Preliminary results support this interpretation. Longitudinal macrodispersivity shows a considerable influence on groundwater life expectancy. Strongly non-linear results are also obtained depending on the transverse vertical dispersivity. Increasing the transverse dispersivity up to a certain threshold leads to an increase of the maximum life expectancy in the model domain. Above this threshold, which depends on the longitudinal dispersivity, the maximum life expectancy decreases. Life expectancy also strongly increases with a decreasing diffusion coefficient. These results highlight the importance of considering uncertainty in the transport parameters when numerically evaluating groundwater life expectancy in density-dependent flow in the context of nuclear waste disposal.

How to cite: Suilmann, J., Molson, J., and Graf, T.: Groundwater life expectancy simulations in strongly coupled density-dependent flow above a salt dome, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7840, https://doi.org/10.5194/egusphere-egu24-7840, 2024.

X4.150
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EGU24-17411
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ERE3.2
Tuong Vi Tran, Aaron Peche, Katrin Brömme, Robert Kringel, and Sven Altfelder

Understanding the movement of radionuclides over time is crucial for assessing the integrity of geological formations as barrier for a radionuclide waste repository. Long-term groundwater potential time series enable the modelling of flow and transport scenarios, which help to predict how radionuclides may migrate from the repository through the overburden into the biosphere, if the overburden as geological barrier should fail. The accuracy of numerical flow and transport models depend on the availability of reliable input data, such that long-term groundwater potential time series help to ensure that numerical flow and transport scenarios accurately represent the complex hydrogeological processes occurring over time.

However, in practice it is very common that, due to financial constraints, vandalism of measurement devices, and other logistical problems result in shorter and/or longer gaps in the ideally continuous groundwater monitoring time series. These gaps can significantly hinder the reliability and completeness of the dataset, making it challenging to perform accurate analyses.

In response to these challenges, we use machine-learning methods with monthly precipitation data from the German meteorological service (DWD), monthly groundwater recharge data generated from the hydrological model RUBINFLUX and continuous groundwater time series from state run monitoring wells as inputs to predict the missing gaps in the groundwater potential time series in the overburden of the radioactive waste repository Morsleben (ERAM).

This approach highlights the importance of continuity in the dataset for further studies, modelling, and safety assessments for radioactive waste repositories. Using machine learning techniques can help to reconstruct the missing data and provide a more comprehensive and continuous dataset for validating and calibrating numerical flow and transport models. 

 

References:

Bear, J., 1972. Dynamics of Fluids in Porous Media. American Elsevier, New York.

Langkutsch, U., Käbel, H., Margane, A., & Schwamm, G. (1998). Planfeststellungsverfahren zur Stillegung des Endlagers für radioaktive Abfälle Morsleben. 457. 

Peche, A., Kringel, R., Orilski, J., & Skiba, P. (2021). Hydrogeologische Modellbildung des ERA Morsleben. In Zwischenbericht Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) im Auftrag der Bundesgesellschaft für Endlagerung (BGE).

Hölting, B., & Coldewey, W. G. (2013). Hydrogeologie. In Hydrogeologie. Spektrum Akademischer Verlag. https://doi.org/10.1007/978-3-8274-2354-2

Zepp, H., König, C., Kranl, J., Becker, M., Werth, B., & Rathje, M. (2017). Implizite Berechnung der Grundwasserneubildung (RUBINFLUX) im instationären Grundwasserströmungsmodell SPRING. Eine neue Methodik für regionale, räumlich hochaufgelöste Anwendungen. Grundwasser, 22(2), 113–126. 
https://doi.org/10.1007/S00767-017-0354-3

How to cite: Tran, T. V., Peche, A., Brömme, K., Kringel, R., and Altfelder, S.: Machine learning-based prediction of gaps in groundwater time series in the overburden of the Morsleben radioactive waste repository, Germany, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17411, https://doi.org/10.5194/egusphere-egu24-17411, 2024.

X4.151
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EGU24-15040
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ERE3.2
Jaehoon Choi, Jeong-Hwan Lee, SunJu Park, Hyunsoo Seo, and Seong-Taek Yun

Geothermal resources have been emerged as a practical and cost-effective clean energy alternative to fossil fuels in many countries. The study of geothermal water can provide valuable insights for sustainable long-term utilization of geothermal energy and for understanding deep geologic environments for diverse emerging geo-energy technologies. For this study, chemical and isotopic tracers (δ2H, δ18O, δ13C, 14C) of thermal groundwaters over South Korean peninsula were investigated to evaluate their geochemical characteristics and reservoir parameters (i.e., temperature, recharge and circulation depth of groundwater, and circulation dynamics). Based on geochemical characteristics, geologic setting, and geographical location, South Korean thermal groundwaters were categorized into five groups (Kim et al., 2020): saline, CO2-rich, high-pH alkaline, sulfate-rich, and diluted freshwater. These distinct hydrochemical characteristics are determined by complex geochemical processes which include calcite dissolution, plagioclase feldspar hydrolysis, CO2 gas dissolution, cation exchange, precipitation of secondary minerals (clay, calcite, fluorite), gypsum dissolution, and seawater mixing. However, each group tends to show no systematic change among outflowing temperature, hydrochemistry, and stable isotopes over time (i.e., radiocarbon age), which may indicate that thermal waters have reached an equilibrium through deep circulation over very long periods of time (millennial scales). All groups of thermal water originated from deeply circulated meteoric water, and their stable water isotope data (δ2H, δ18O) show a systematic fractionation pattern depending on the recharge altitude (Choi et al., 2023). Temperatures of geothermal reservoirs at depths were estimated by using chemical geothermometers considering the ambient geology and measured outflow temperatures. The results obtained from K-Mg, Li-Mg, Na-K-Ca, Na-K, and Si geothermometers ranged widely from a minimum of 28°C to a maximum of 207°C, with an average of 61 to 148°C. The estimated depths of groundwater circulation to form South Korean thermal waters fall between about 1.0 and 3.3 km, if calculate from the calculated average reservoir temperature and geothermal gradient data in each location. The estimated circulation depths tend to increase with decreasing stable water isotope data (δ2H, δ18O) and increasing radiocarbon (14C) ages. This study, conducted across South Korea, provides important information about the origin and evolution of deep thermal water, which may be helpful to the efficient and sustainable management of geothermal resources and to the selection of suitable sites for geologic CO2 storage or high-level radioactive waste disposal. Acknowledgements: This study was supported by the Institute for Korea Spent Nuclear Fuel (iKSNF) and the BK Plus project in Korea.

References

Choi, J., Yu, S., Park, S., Yun, S.T., Lee, J., Park, J. (2023). Hydrochemical and Isotopic Assessment of Deep Groundwater: Residence Time, Circulation and Inter-Aquifer Mixing in South Korea. Goldschmidt 2023 Abstracts. https://doi.org/10.7185/gold2023.20028

Kim, K.H., Yun, S.T., Yu, S., Choi, B.Y., Kim, M.J., Lee, K.J. (2020). Geochemical pattern recognitions of deep thermal groundwater in South Korea using self-organizing map: identified pathways of geochemical reaction and mixing. Journal of Hydrology 589, 125202. https://doi.org/10.1016/j.jhydrol.2020.125202

How to cite: Choi, J., Lee, J.-H., Park, S., Seo, H., and Yun, S.-T.: Investigating Geochemical Characteristics of South Korean Geothermal Waters and Their Reservoir Condition Using Combined Hydrogeochemical, Isotopic and Geothermometric Approaches, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15040, https://doi.org/10.5194/egusphere-egu24-15040, 2024.

X4.152
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EGU24-16083
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ERE3.2
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ECS
Raphael Burchartz, Mohammadreza Jalali, Sebastian Grohmann, Lisa Winhausen, Garri Gaus, Timo Seemann, Jochen Erbacher, Ralf Littke, and Florian Amann

Characterizing the host rocks for high-level radioactive waste disposal requires considering various rock parameters such as petrophysical (e.g., porosity, permeability and storativity) as well as mechanical (e.g., Young’s modulus) properties. The burial history and thermal maturity of rock formations, particularly shale, significantly affect these properties. Understanding the relationship between the thermal maturity and the referred properties is essential for transferring data among various test sites.

Pliensbachian shales (Lower Saxony Basin, Hils area) are characterized by a notably homogenous mineral composition. Previous studies on this formation suggest a highly variable burial history over a lateral distance of about 50 km, reaching maximum burial depths between 1300 m in the southeast to 3600 m in the northwest of this region (Gaus et al., 2022; Littke et al., 1987, 1991). In the context of the MATURITY project, eight boreholes were drilled at five different locations with varying thermal maturity along this axis. Geophysical well logging was carried out in all boreholes to investigate mineralogical (clay mineral content), petrophysical (porosity), and rock mechanical properties (e.g., dynamic Poisson's ratio). First results revealed a homogeneous clay mineralogy in all boreholes. However, significant differences were observed in both the dynamic-elastic behavior and porosity of the investigated shale formation at different locations. The obtained data can be used to establish correlations between burial history and various shale rock properties, contributing to a site-independent characterization of shale formations for long-term disposal of high-level nuclear waste.

 

 References

  • Gaus, G., Hoyer, E.M., Seemann, T., Fink, R., Amann, F., Littke, R. (2022). Laboratory investigation of permeability, pore space and unconfined compressive strength of uplifted Jurassic mudstones: The role of burial depth and thermal maturation. Zeitschrift der Deutschen Gesellschaft für Geowissenschaften, 173 (3), 469-489
  • Littke, R., Baker, D. R., & Leythaeuser, D. (1988). Microscopic and sedimentologic evidence for the generation and migration of hydrocarbons in Toarcian source rocks of different maturities. Advances in Organic Geochemistry, Vol.13(Nos 1-3), 549–559.
  • Littke, R., Leythaeuser, D., Rullkötter, J., & Baker, D. R. (1991). Keys to the depositional history of the Posidonia Shale (Toarcian) in the Hils Syncline, northern Germany. Geological Society, London, Special Publications, 58(1), 311–333.

How to cite: Burchartz, R., Jalali, M., Grohmann, S., Winhausen, L., Gaus, G., Seemann, T., Erbacher, J., Littke, R., and Amann, F.: The Influence of Burial History on the In-situ Petrophysical and Mechanical Characteristics of Pliensbachian Shale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16083, https://doi.org/10.5194/egusphere-egu24-16083, 2024.

X4.153
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EGU24-19823
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ERE3.2
Vanessa Montoya and Koen Beerten

Climate evolution over millennial timescales significantly influences various environmental aspects, including thermal conditions, regional sea levels, geomorphological evolution, weathering processes, and hydrogeological evolution. This intricate relationship has direct implications for nuclear waste management facilities, as climate change alters the frequency and intensity of extreme events, posing risks during construction, operation, and post-closure phases. Understanding these impacts is crucial for ensuring safety and to building civil society's confidence in radioactive waste management programes. This contribution centers on Belgian scenarios.

SCK CEN, with extensive experience in studying climate change impacts on nuclear waste management, shares its insights from projects such as BIOCLIM, BIOMOSA, and EURAD. The Belgian case, with its diverse climate regions, offers valuable data applicable to other countries facing similar climate challenges. For example, SCK CEN's involvement in EURAD - UMAN has already prompted recommendations for managing uncertainties in the geosphere, particularly in climatic evolution. Key areas of focus could include validating permafrost depth models, modeling hydrochemical changes resulting from permafrost development, conducting detailed palaeo-hydrological studies, and considering the influence of decompaction on host rock properties. This study serves as a critical resource for understanding and addressing climate-related challenges in nuclear waste management, fostering international collaboration and knowledge exchange.

How to cite: Montoya, V. and Beerten, K.: Climate Change Impacts on Nuclear Waste Management: Insights from Belgium and Recommendations for Future Research, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19823, https://doi.org/10.5194/egusphere-egu24-19823, 2024.

X4.154
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EGU24-3920
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ERE3.2
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ECS
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Highlight
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Ji-Min Choi, Soolim Jung, Doohee Jeong, Nak Kyu Kim, Kyung-Woo Park, and Young-Seog Kim

High-level radioactive waste repositories rely on multi-barrier systems, including natural and engineered barriers, crucial for long-term safety through isolation and delay functions. Improving the performance of natural barriers poses challenges, necessitating thorough evaluation via ongoing field surveys and lab tests. Natural barriers are categorized and analyzed based on lithological and structural characteristics. Structural elements such as fractures, joints, and faults play a crucial role in performance assessment as they can serve as pathways for groundwater flow. Existing studies lack a unified criterion for defining structural boundaries, prompting a systematic review to establish standards suitable for site characteristics by applying various structural factors to study area boreholes. Considering the deep location of the disposal site, borehole data plays a pivotal role. The KAERI Underground Research Tunnel (KURT) is a small-scale Underground Research Laboratory (URL) with a maximum depth of 120 m excavated within the Korea Atomic Energy Research Institute (KAERI). The boreholes used in the study were drilled to depths ranging from approximately 500 to 1,000 m within the site, including KURT. The preliminary fracture zone was identified through frequency analysis of gaps between fractures in the borehole images. As reviewed previously, the methods for defining the fracture zone can broadly emphasize the background fracture and presenting exclusion conditions or emphasize the dense area of fractures and presenting boundary conditions. For each method, the match rate with the preliminary fracture zone was validated. To confirm the correlation between the match rate and the natural state, it was compared with the actual fracture density found in the drill core. By integrating a series of processes, we could quantify standards for defining deep fracture zones using boreholes. The results of this study will contribute to a three-dimensional model of the deep brittle structure within the natural barriers. Future research can explore the identified fracture zone, surface fracture zone, and the definition of fault zones with fault rocks.

Keywords: Deep fracture zones, background fracture, brittle structure, Borehole data, KURT

Acknowledgements: This research was supported by the Institute for Korea Spent Nuclear Fuel (iKSNF) and National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT (MSIT) (2021M2E1A1085200).

How to cite: Choi, J.-M., Jung, S., Jeong, D., Kim, N. K., Park, K.-W., and Kim, Y.-S.: Characterizing deep fracture zones within the natural barrier: Insights from borehole data around the KAERI underground research tunnel, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3920, https://doi.org/10.5194/egusphere-egu24-3920, 2024.

X4.155
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EGU24-7277
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ERE3.2
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Highlight
Yuxin Wu, Jiannan Wang, Hang Chen, Linqing Luo, Shawn Otto, Kristopher Kuhlman, Liange Zheng, and Jens Birkholzer

The distinctive properties of salt, such as low permeability, high thermal conductivity, and self-sealing features, make it a suitable medium for storing heat-generating radioactive waste. Understanding the thermal, hydrological, and mechanical (THM) processes, including permeability evolution and brine migration around the heat source, is crucial for safety. The Brine Availability Tests in Salt (BATS) at the Waste Isolation Pilot Plant were conducted to investigate these processes, employing an array of sensors and techniques like electrical resistivity tomography (ERT), fiber optic distributed temperature sensing (DTS), and strain sensing (DSS). These techniques monitored temperature changes, brine movement, and stress conditions in the salt.

This presentation highlights the results from ERT, DTS, and DSS in controlled heating experiments, focusing on the response differences across various heating events. The analysis, augmented by Discrete Element Models (DEM) simulations, showed that resistivity changes were sensitive to temperature and brine movement. A significant decrease in resistivity, especially beyond temperature effects, indicated brine migration or permeability changes. The DTS and DSS data captured the evolving thermal and mechanical responses of the salt to heating and cooling cycles, including salt deformation, and creeping towards the drift wall.

Joint analysis of ERT, DTS, and DSS data provided an integrated understanding of THM processes in salt during heating. Consistent heating and brine migration patterns were observed across different events. Ongoing work aims to combine all monitoring data for a deeper insight into the coupled behaviors in salt formations, offering valuable calibration and benchmarking for numerical models.

How to cite: Wu, Y., Wang, J., Chen, H., Luo, L., Otto, S., Kuhlman, K., Zheng, L., and Birkholzer, J.: Geophysical Understanding of Coupled Thermal-Hydro-Mechanical Dynamics in Rock Salt During Heating, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7277, https://doi.org/10.5194/egusphere-egu24-7277, 2024.

X4.156
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EGU24-13566
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ERE3.2
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ECS
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Gabriel Iklaga, Nándor Kaposy, Istvan Tolnai, Viktória Gável, Margit Fábián, Csaba Szabó, Péter Völgyesi, and Zsuzsanna Szabó-Krausz

Boric acid is used in pressurized water reactor (PWR) systems as an efficient neutron absorber for activity control which aids in the maintenance of steady state operating temperature control. The boric acid liquid waste produced from the system might contain low concentrations of nuclear fission produced radioisotopes such as 137Cs and its metastable decay product 137mBa (also named as 137mCs). Adequate repository storage of this high-volume liquid waste has become environmentally important for study as these radioisotopes can become bio-available in the natural systems if not effectively immobilized. Our research main aims are to assess the geochemical effects of natural zeolite (i.e., clinoptilolite and mordenite) additives in sulfoaluminate cement (SAC) and ordinary Portland cement (OPC) blends for optimizing chemical and mechanical stability for immobilizing boric acid liquid waste and contained fission isotopes, mentioned above in solidified cement paste waste forms.

To accomplish our research goal, the natural zeolite additives at ratios ranging from 0%, 5%, 10%, 15% and 20%, respectively, were added to a benchmarked OPC to SAC blend (i.e., 80% OPC to 20% SAC) based on results from our previous experiments. The samples were then mixed with simulated boric acid liquid waste containing Cs and Ba isotopes and allowed to cure for 28 days. Standardized reference leaching test was carried out on the cured solid waste forms for 11 days and then they were analyzed by standardized compressive strength test, scanning electron microscopy (SEM) for morphology and X-ray diffraction (XRD) for mineralogy. While the liquid waste solutions (leachate) from the leaching test were analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectroscopy (ICP-MS) to assess elemental and isotopic changes.  

How to cite: Iklaga, G., Kaposy, N., Tolnai, I., Gável, V., Fábián, M., Szabó, C., Völgyesi, P., and Szabó-Krausz, Z.: Physical and chemical effects of natural zeolites additives on the cementitious stabilization of cesium and barium isotopes in boric acid liquid waste  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13566, https://doi.org/10.5194/egusphere-egu24-13566, 2024.

X4.157
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EGU24-3648
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ERE3.2
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ECS
Amber Zandanel, Alyssa McKanna, Marlena Rock, Kirsten Sauer, and Florie Caporuscio

Long-term stability of engineered barrier system (EBS) materials in repository conditions is a primary concern for radioactive waste repository success. EBS designs generally include bentonite as barrier between the canister and host rock to provide: 1) a physical barrier to prevent natural fluid from interacting with the waste package and 2) a chemical barrier that attenuates radionuclide migration. Bentonite interaction with host rock and groundwater in water-saturated geologic repositories may result in the formation of secondary minerals that affect the sealing properties of the bentonite. Specifically, the formation of zeolites may negatively affect bentonite swelling properties but may also help attenuate radionuclide migration through sorption and incorporation into zeolite structures. Here we discuss the experimental formation of analcime-group zeolite minerals with Na-, Ca-, and Cs-endmembers (analcime, wairakite, and pollucite, respectively) through hydrothermal bentonite alteration in geologic repository conditions.

Experimental work was conducted at elevated pressure and temperatures conditions relevant to underground repositories. High-pressure Cs-bentonite experiments were completed from 150-400 °C and 500-1000 bar for 14 to 62 days. Gold capsules were loaded with a 2:1 water:rock ratio of unprocessed bentonite from Colony, Wyoming and an aqueous fluid containing 2 molal CaCl + CsCl + NaCl with an initial pH of ~5.8. At 200 °C Cs was found to be entrained in different phases including the zeolite clinoptilolite. Clinoptilolite is an accessory mineral in the initial bentonite mineral assemblage and the results suggest incorporation into existing clinoptilolite rather than any Cs-clinoptilolite precipitation. At reaction temperatures ≥ 300 °C and < 450 °C we observed newly precipitated crystals of pollucite in the bentonite matrix. After reaction at 450 °C only trace amounts of Cs were identified in mineral phases: instead, we observed the formation of analcime-wairakite minerals with little or no pollucite formation. Comparing these results to analcime-wairakite-pollucite stability at a range of pressure-temperature conditions sheds light on conditions that promote Cs immobilization through incorporation in pollucite crystal structures. These results expand the range of experimentally observed zeolite formation and define pressure and temperature fields that promote Cs entrapment during hydrothermal bentonite alteration. The potential benefits of radionuclide immobilization through zeolite formation are contextualized by thermodynamic and kinetic geochemical modelling of Na-, Ca-, Cs-zeolite formation and the anticipated effects to bentonite and EBS properties over time.

How to cite: Zandanel, A., McKanna, A., Rock, M., Sauer, K., and Caporuscio, F.: Temperature and reaction time dependence of (Na,Ca,Cs)-zeolite formation., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3648, https://doi.org/10.5194/egusphere-egu24-3648, 2024.

X4.158
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EGU24-18345
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ERE3.2
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ECS
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Carla Soto Ruiz, Úrsula Alonso de los Ríos, Tiziana Missana, and Pedro Pablo Valdivieso Mayoral

Deep geological repository (DGR) is the best solution for confining high-level radioactive waste (HLRW). DGRs are multibarrier systems, where a metallic container of carbon steel or other metals is surrounded by a compacted bentonite barrier confining the waste, and placed in adequate geological formation. The purpose of DGRs is to delay the migration of radionuclides (RN) into the biosphere until the radiation was inoffensive.

Bentonite is a clay with high stability. Its durability depends on the physical, chemical, thermal and mechanical conditions of the repository and may be affected by the radiation emitted by the waste.

The objective of this research is to compare the surface properties of gamma-irradiated and unirradiated bentonite (Ca-Mg FEBEX bentonite) to evaluate if the irradiation from the radioactive waste encapsulated in the metallic container modifies.

To evaluate the effect of the accumulated dose, the bentonite was subjected to two rounds of irradiations during 9 days with a 60Co source in pool like installation achieving cumulative gamma doses of 14 kGy and 140 kGy.

The structural characteristics of irradiated and unirradiated bentonite samples are analysed by infrared spectroscopy [1] to identify changes in functional groups of the clays. Zeta potential measurements as well as potentiometric titrations to obtain information on the density of SOH hydroxyl surface groups on the edges of clay particles. All these properties are essential for the adsorption capacity of the material.

Lastly, the sorption capacity of irradiated bentonite was evaluated by measuring Sr and Se sorption isotherms at fixed pH and ionic strength conditions, representative elements with different sorption mechanism on bentonite, to be compared to the unirradiated bentonite [2], [3].

Results showed that the analysed properties were slightly affected by gamma-irradiation in the doses investigated.

 

 

ACKNOWLEDGEMENTS: The authors would like to thank the finance of this research to the CIEMAT predoctoral fellowship (209-PRECIE-PDE22) through the European Union Project, EURAD-WP ConCorD, Grant Agreement no. 847593.

 

REFERENCES

 

[1] Madejova, J., Komadel, P. 2001. Baseline studies of the clay minerals society source clays: infrared methods. Clays and clay minerals, 49(5), 410-432.

[2] Mayordomo, N., Alonso, U., & Missana, T. (2016). Analysis of the improvement of selenite retention in smectite by adding alumina nanoparticles. Science of The Total Environment, 572, 1025-1032.

[3] Missana, T., Garcia-Gutierrez, M., & Alonso, U. (2008). Sorption of strontium onto illite/smectite mixed clays. Physics and Chemistry of the Earth, Parts A/B/C, 33, S156-S162.

How to cite: Soto Ruiz, C., Alonso de los Ríos, Ú., Missana, T., and Valdivieso Mayoral, P. P.: Effect of gamma-irradiation on the surface and adsorption properties of bentonite clay, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18345, https://doi.org/10.5194/egusphere-egu24-18345, 2024.

X4.159
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EGU24-17828
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ERE3.2
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ECS
Deepa Bartak, Šárka Šachlová, Vlastislav Kašpar, Jakub Říha, Petr Večerník, Veronika Hlaváčková, and Kateřina Černá

Bentonite is a crucial part of the engineered barrier system (EBS) of the deep geological repositories (DGR) for nuclear waste. However, as a natural material, it harbors diverse indigenous microorganisms whose metabolic activity might compromise the long-term integrity of EBS. One of the critical questions for microbial activity prediction in DGR is the microbial reaction to the early hot phase of nuclear waste repository evolution. Our study investigates the impact of gamma radiation and heat on microbial survivability in bentonite (Czech bentonite BCV and reference bentonite MX-80), considering variations in compaction, temperature, and saturation levels as these factors are known to influence microbial reaction to extreme conditions. Previous results suggested average radiation tolerance and high heat tolerance of indigenous bentonite microorganisms. We aimed to confirm these findings during the medium-term experiment (18 months) at the repository simulating conditions. Four experimental setups were conducted using compacted BCV and MX-80 bentonites under anoxic conditions differing in initial saturation level (15-20 wt. %), heating temperature ( 90 or 150°C), and irradiation (0.4 Gy/h). An additional set of bentonite powder samples heated at 90°C or 150°C for 1, 3, and 6 months was further included to unravel the time effect of heat exposure on microbial survivability. Microbial community analysis, involving natural incubations in the form of bentonite suspension, enrichment cultures, microscopy, and molecular methods, was conducted for each sample to estimate microorganism survival following exposure to extreme conditions.

Contrary to expectations, no microbial growth and recovery were detected in any treated samples except for the additional set. Fresh samples, suspension incubations, and enrichment cultures were checked negative for microbial presence in almost all the cases in the four main experimental sets except for the positive controls. On the other hand, the samples from the additional set showed microbial recovery after heating at 90°C for 1, 3, and 6 months. However, exposure to 150°C for only 1 month resulted in bentonite sterilization. These medium-term data pointed out the high tolerance of indigenous bentonite microorganisms to heat but also indicated that developing a sterile bentonite layer in the proximity of hot and radiation-emitting metal canister is highly likely at the early stage of the DGR evolution. However, the particular development will depend upon the DGR design and actual levels of temperatures and irradiation. To enhance our understanding and predictability of microbial processes in the bentonite sealing layer of DGRs for nuclear waste, further microbiological experiments simulating conditions in distant bentonite layers subjected to lower temperature and studying potential microorganism penetration from non-sterile to sterilized zones are needed.

How to cite: Bartak, D., Šachlová, Š., Kašpar, V., Říha, J., Večerník, P., Hlaváčková, V., and Černá, K.: Assessing microbial activity and survivability in heated and irradiated bentonite samples under deep geological repository relevant conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17828, https://doi.org/10.5194/egusphere-egu24-17828, 2024.

X4.160
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EGU24-7345
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ERE3.2
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Highlight
FE-G: Gas dynamics over 10 years at the Full-Scale Emplacement experiment (Mont Terri, CH) 
(withdrawn)
Emiliano Stopelli, Typhaine Guillemot, Myriam Agnel, Scott Briggs, Fraser King, Rolf Kipfer, Simon Norris, Nikitas Diomidis, and Irina Gaus
X4.161
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EGU24-18849
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ERE3.2
Vanessa Montoya and Jaime Garibay-Rodriguez

In this contribution we have developed a reactive transport model to assess the hydro-chemical evolution of a L-ILW disposal cell in indurated clay rocks, involving the interaction of different components/materials and the expected hydraulic and/or chemical gradients over 100 000 years. The L-ILW disposal cell leverages a multi-barrier concept buried between 200 and 800 m below the surface. The multi-barrier system is comprised of the waste matrix (i.e. backfilling the waste drums), the disposal container, the mortar backfill in the emplacement tunnel (where the disposal containers are located) and the clay host rock. The dimensions and design of the emplacement tunnel (e.g. 11 × 13 m) and disposal cells represent and consider some aspects taken into account in the designs of some European countries. In addition, tunnel walls reinforced with a shotcrete liner and the Excavation Damaged Zone is considered in the concept. The model is implemented in OpenGeoSys-6, an open-source version-controlled scientific software based on Finite Element Method which is capable of handling fully coupled hydro-chemical models by coupling OpenGeoSys to iPHREEQC. First calculation results, demonstrate that the most important processes affecting the near-field chemical evolution are i) the degradation of the concrete and cementitious grouts with porewater migrating inwards from the host rock and ii) the significant quantities of reactive and non-reactive gases (i.e. hydrogen, carbon dioxide and methane) that are generated as a result of: i) the anaerobic corrosion of metals present in the waste and containers and ii) the degradation of organic compounds by microbial and chemical processes. Several simulation cases were carried out under different assumptions, specially related to the saturation of the domain, the final goal was to have a 2D model of the system representing a more realistic geometry which will potentially help in design optimization decisions.

How to cite: Montoya, V. and Garibay-Rodriguez, J.: 2D reactive transport model for assessing the chemical evolution of a low and intermediate-level waste repository in clayrock, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18849, https://doi.org/10.5194/egusphere-egu24-18849, 2024.

X4.162
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EGU24-21286
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ERE3.2
Diederik Jacques and Vanessa Montoya and the EURAD - ACED Team:

The European Union’s Horizon 2020 project EURAD (European Joint Progamme on Radioactive Waste Management) aim is to implement a joint Strategic Programme of research and knowledge management activities at the European level, bringing together and complementing EU Member State programmes in order to ensure cutting-edge knowledge creation and preservation in view of delivering safe, sustainable and publicly acceptable solutions for the management of radioactive waste across Europe now and in the future. The broader scope of the work package ACED (Assessment of the chemical evolution in intermediate and high level radioactive waste disposal cells) in EURAD is the assessment of the chemical evolution at the disposal cell scale involving interacting components/materials and thermal, hydraulic and/or chemical gradients. Four generic disposal cells that are representative for the most important aspects of disposal designs in several national disposal programs throughout Europe, formed the basis for the research activities in this work package.

Conceptual, mathematical and numerical models were developed and implemented to describe the geochemical evolution in the combined engineered barrier system and the immediately surrounding host formation (clay or granite) from a more detailed scale up to a spatial scale of a few meters and time scales up to 100 000 y. ACED demonstrated the applicability of advanced coupled reactive transport models to provide an integrated view on coupled geochemical processes in the multi-barrier system of a deep geological repository. Insight in the geochemical evolution was obtained from more detailed numerical models at the scale of the waste package (neglecting influences from the host rock) up to models with the detailed geometry and the different materials in the disposal scale (depending on the system including nuclear glass, organic waste, metallic waste, steel, cementitious materials, bentonite, and host rock). Beside models that integrated as detailed as possible the available information, approaches were tested to decrease the model complexity while preserving the key findings of the more complex models; a process also known as model abstraction. Simplifications were made with respect to dimensionality, chemical complexity and numerical accuracy as well by implementing surrogate models based on machine learning tools to replace the parts of the models requiring the most computational time.

ACED made a significant step forward in process-based modelling of geochemical interactions  in the near field of a geological repository where the engineered barrier system interacts with the host rock. The models and insights obtained for the generic disposal cells can form a basis for more specific research studies in national disposal programs.

Acknowledgement: The research leading to these results was funded by the EURAD work package (European Joint Programme on Radioactive Waste Management of the European Union, EC grant agreement nº 847593)

How to cite: Jacques, D. and Montoya, V. and the EURAD - ACED Team:: EURAD ACED – Modelling the geochemical evolution of disposal cells in deep geological repositories, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21286, https://doi.org/10.5194/egusphere-egu24-21286, 2024.

X4.163
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EGU24-21252
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ERE3.2
Lucie Mareda, Igor Soejono, Zita Bukovská, Ondřej Švagera, Lenka Rukavičková, Jaroslav Řihošek, Jakub Kry, Tereza Zelinková, Tomáš Chabr, Radek Morávek, Kamil Souček, Martin Vavro, Petr Waclawik, Karel Sosna, Jiří Nedvěd, Lukáš Mareček, and Anna Macáková

​In order to place experiments in real geological conditions, a new section of the already active generic underground research facility Bukov (Bukovská et al. 2019) is recently being constructed. It is located in the central Bohemian Massif, in former uranium mine Rožná, at c. 550 m below the surface. During the excavation of new tunnels and laboratory chambers, a complex of geomechanical, structural, geological, hydrogeological and geophysical measurements and monitoring activities is continuously performed. The main objectives of this in-situ characterization project are to understand and 3D visualize the structural record and its hydrogeological systematics. Other objectives are to determine the excavation damage zones, the effect of blasting, the physical and mechanical properties of the rocks, and testing the excavation and drilling methodology.

The laboratory is situated mostly in the intensively deformed paragneiss, high-grade amphibolites and migmatites, typical for the European Variscan belt. Geological observations have revealed a complex polyphase deformational pattern of metamorphic foliations, strongly influencing the superposed fault and fracture systems, hydrogeological conditions and rock mass properties. Based on multidisciplinary research of borehole and tunnel data, possible problematical geological structures are identified and investigated. Finally, all obtained data and experience will serve to development of work-flows of documentation and rock-mass suitability classification system during building of the future real deep geological repository.

The construction will be completed in 2024 and the underground research facility will become part of the national planning and siting strategy for the deep underground repository for high-level radioactive waste. The data from this research will contribute to the understanding of the geology of the region and will be used for experiments addressing long-term safety and technical feasibility. Such results from the depth can allow correlation and validation of data collected from surface research (Soejono et al. 2021) in the potential sites for deep geological repository construction.

 Bukovská, Z., Soejono, I., Vondrovic, L., et al., 2019. Characterization and 3D visualization of underground research facility for deep geological repository experiments: A case study of underground research facility Bukov. Czech Republic. Eng. Geol. 259, 105186. https://doi.org/10.1016/j.enggeo.2019.105186

Soejono, I., Bukovská, Z., Levá, B., et al., 2021. Interdisciplinary geoscientific approach to radioactive waste repository site selection: the Březový potok site, southwestern Czech Republic. J. Maps 17, 741–749. https://doi.org/10.1080/17445647.2021.2004942

How to cite: Mareda, L., Soejono, I., Bukovská, Z., Švagera, O., Rukavičková, L., Řihošek, J., Kry, J., Zelinková, T., Chabr, T., Morávek, R., Souček, K., Vavro, M., Waclawik, P., Sosna, K., Nedvěd, J., Mareček, L., and Macáková, A.: New underground research facility for deep disposal of radioactive waste Bukov II, Czech Republic: objectives, geological constraints and current status, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21252, https://doi.org/10.5194/egusphere-egu24-21252, 2024.

X4.164
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EGU24-12859
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ERE3.2
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ECS
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Qian Chen, Marc S. Boxberg, Nino Menzel, Maria F. Morales Oreamuno, Wolfgang Nowak, Sergey Oladyshkin, Florian M. Wagner, and Julia Kowalski

Given the importance of ensuring the safe disposal of radioactive waste, it is vital to understand the targeted subsurface systems and to build physics-based models to predict their dynamic responses to human interventions. Constructing robust predictive models, however, is very challenging due to the systems’ complexity as well as the scarcity and cost of geophysical data acquisition. Optimal matching of data acquisition and predictive simulations is therefore necessary and can be achieved via integrating predictive process modeling, Bayesian parameter estimation, and optimal experimental design into a modular workflow. This allows to quantify the information content of measurement data and therefore enables optimal planning of data acquisition and monitoring strategies. Conducting such data-integrated simulation studies, however, requires a robust workflow management that ensures reproducibility, error management, and transparency. 

To meet this demand, we established a data-centric approach to workflow control combining error-managed simulations with a functional data hub, providing simulations with direct access to a database of essential material properties. The latter are being made available as site specific scenario compilations along with uncertainty margins and meta information.  

The data hub serves as an interface facilitating seamless data and simulation exchange to support subsequent model-driven decision-making processes and guarantees that simulations are conducted using manageable, comparable, and reproducible test cases. Furthermore, it ensures that the simulation results can be readily transferred to a designated repository allowing for real-time updates of the model. The implementation of the data hub is based on a Python-based framework for two different use cases:

1)  GUI-based use case: The graphical user interface (GUI) facilitates data import, export, and visualization, featuring distinct sections for geographic data representation, structured table organization, and comprehensive visualization of physical properties in varying dimensions.

2) Module-based use case: Built on the YAML-based data-hub framework, it enables direct integration of simulation modules storing measurements and model parameters in the YAML data format.

The data is systematically organized to furnish a versatile data selection framework that allows information to be extracted from a variety of references, including specific on-site measurements, laboratory measurements and other references, thereby enabling a comprehensive exploration of different reference-oriented scenarios.

This study showcases the data hub as a management infrastructure for executing a modular workflow. Multiple models—such as process and impact models as well as their surrogates and geophysical inverse models—are generated within this workflow utilizing scenarios provided by the data hub. Our study shows that adopting a data-centric approach to control the simulation workflow proves the feasibility of conducting different data-integrated simulations and enhances the interchangeability of information across different stages within the workflow. The paradigm of sustainable model development ensures reproducibility and transparency of our results, while also offering the possibility of synergetic exchange with other research areas. 

How to cite: Chen, Q., Boxberg, M. S., Menzel, N., Morales Oreamuno, M. F., Nowak, W., Oladyshkin, S., Wagner, F. M., and Kowalski, J.: The site selection data hub: a data-centric approach for integrated simulation workflow management in radioactive waste disposal site selection, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12859, https://doi.org/10.5194/egusphere-egu24-12859, 2024.