In the current phase of the German Site Selection Procedure for a deep geological repository, large areas of Germany’s subsurface are being screened in order to identify the most-suited regions. A key screening tool for this purpose is the preliminary safety assessment, which allows a gradual reduction of these vast areas to a series of relatively small high-potential regions.
The portfolio of potential host rocks includes claystone, rock salt and crystalline rocks. These geological formations can exhibit significantly different properties and key subsurface uncertainties relevant to a geological repository.
Additionally, in alignment with the regulations, only existing subsurface data are used during this screening phase, i.e. data acquired for other purposes, such as hydrocarbon, ore and potash exploration, geothermal energy etc. Hence, the available dataset is heterogeneous, both in terms of data types and in terms of geographical distribution.
The estimation of the subsurface uncertainties is relevant for the robustness evaluation during the safety assessment. Consequently, the uncertainty estimation concept includes methods for different scales: screening methods applicable to large areas and detailed methods applicable to the relatively small high-potential regions.
For large areas with heterogeneous data, a semi-quantitative method for a consistent and efficient assessment of the subsurface uncertainties was developed. This method estimates a “degree of confidence”, which represents the reliability of given statements concerning the interpretation of the subsurface. The “degree of confidence” can be estimated for each given area from the combination of data quality and quantity, on one the hand, and the geological complexity, on the other. For the smaller, high-potential areas, quantitative methods of estimation of the uncertainties are used. These can include statistical and geostatistical approaches.
How to cite: Derer, C., Reyer, D., Kreye, P., and Sander, C.: Assessing subsurface uncertainties during the screening of large areas for a deep geological repository for high-level radioactive waste, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1483, https://doi.org/10.5194/egusphere-egu25-1483, 2025.
Germany is currently conducting a site selection procedure with the quest for an optimal repository site for high-level radioactive waste in geological subsurface. The site selection procedure must be done in accordance with the Final Repository Safety Requirements Ordinance, which restricts the maximum allowable exposure for high-level radioactive waste released from the final repository site. One of the potential risks associated with the repository site is the release of radionuclides through groundwater flow. Therefore, a risk assessment regarding the environmental impact of different hazard scenarios is crucial to carefully select and ensure long-term safety of the repository site.
To assess the risk of radioactive contamination in the subsurface, physics-based process models are implemented to predict the spatial-temporal evolution of the radionuclide concentration associated with a given hazard scenario. The resulting radionuclide concentration provides the basis for impact modelling, namely estimating accumulated dose and subsequently quantifying potential radioactive contamination. Simulations are implemented through the OpenGeoSys software. A supporting Python package, Yaml2Solver, is developed to orchestrate process and impact modelling along with relevant parameters. The package centralizes simulation and material information in YAML files to define and adjust model parameters, and it enables simulating different coupled-level process models.
These data-integrated models, however, are built in the presence of uncertainties in material properties, including permeability of rock and groundwater flow. Accounting for uncertainties in physics-based simulations calls for an effective and reliable uncertainty management tool. We therefore developed an analysis-ready and actionable data-hub. The data-hub consists of a database integrated with a graphic user interface (GUI). The database provides material properties along with their uncertainty margins and sensible defaults in YAML files for analysis readiness of simulation models. The material properties are associated with synthetic, reference, and candidate sites, enabling the compilation of site-specific scenarios for simulations. The GUI provides detailed visualization for each site, including a three-dimensional geostructural model, a chronostratigraphic chart indicating the geological formation time of each stratum, and a table providing information on rock properties and attributes of sensible defaults. The data-hub framework supports for systemic and uncertainty-informed model-based assessment as well as subsequent model-based decision-making tasks. We further integrated the data-hub with Yaml2Solver for efficient uncertainty management across various scenarios.
Data-hub integerated process and impact modelling offers benefits for managing long-term uncertainties and improving reproducibility, and thereby increasing the transparency and reliability of decision-making. Depending on the material properties with their marginal values sourced from different sites, we construct various site-specific process models. Subsequently, the process models are extended to impact models, describing spatial-temporal evolutions of radiation. The resulting uncertainty-informed impact models enable us to quantify potential radioactive contamination in specific sites and offer valuable insights in repository site selection and safety assessments.
How to cite: Chen, Q., Boxberg, M. S., Menzel, N., Wagner, F. M., and Kowalski, J.: Radioactive Contamination Risk Assessment in Long-Term Radioactive Waste Disposal: Actionable Data-Hub for Analysis-Readiness in Process and Impact Models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18973, https://doi.org/10.5194/egusphere-egu25-18973, 2025.
The search for a repository site and its design rely on digital models and simulations. An integral part of the site selection process is the assessment of the integrity of the containment-providing rock zone. Computational models assessing the integrity of geological barriers in repository systems often yield complex results typically accessible only to experts in these disciplines. An extra layer of complexity is added to these results by considering input uncertainties. As the site-selection process progresses, it is becoming increasingly important to make this kind of results accessible to a broader audience to support and facilitate decision-making and improve the acceptance of pre-selected and rejected sites.
Deterministic finite element simulation results are resolved in time and space for each primary variable and each additional post-processed quantity, such as pore water pressure, stresses, temperatures, and integrity criteria. If uncertainty – or, in other words, variability – in the input parameters is considered, the dimensionality of the state space grows with each parameter included in the stochastic or parametric model. A surrogate model is constructed by adaptive sparse grid sampling, efficiently mapping the complete state space. No data is reduced in this step such that a functional dependency between uncertain inputs and complete finite element results is established, enabling finite element result interpolation for any location in the state space. With modern software technologies developed at the Federal Institute for Geosciences and Natural Resources (BGR), the time for querying the surrogate model has been reduced to such an extent that complete finite element results are reproduced in fractions of a second, laying the foundation for a real-time visualization dashboard by which the effect of the change of any uncertain input parameter can be investigated in the complete physical and time domain.
This contribution uses the geological model ANSICHT-II [3] as an example. It represents a generic repository in a clay rock formation of greater thickness without a fixed local reference. Individual simulation runs were performed by OpenGeoSys 6 [4], and the stochastic model was generated by OpenGeoSysUncertaintyQuantification.jl [1]. The interactive dashboard was generated with the help of Makie.jl [2], a flexible, high-performance, cross-platform plotting ecosystem for the Julia programming language. With this dashboard, the user can freely select the most important input parameters (thermal, hydraulic, and mechanical properties of the host rock) within realistic ranges, and the corresponding results are displayed in real time. In addition, the area where integrity violation is to be expected is marked.
[1] Bittens, M. (2024). OpenGeoSysUncertaintyQuantification.jl: a Julia library implementing an uncertainty quantification toolbox for OpenGeoSys. Journal of Open Source Software, 9(98), 6725.
[2] Danisch, S., & Krumbiegel, J. (2021). Makie.jl: Flexible high-performance data visualization for Julia. Journal of Open Source Software, 6(65), 3349.
[3] Maßmann, J., et. al. (2022): ANSICHT-II – Methode und Berechnungen zur Integritätsanalyse der geologischen Barriere für ein generisches Endlagersystem im Tongestein. Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Ergebnisbericht; Hannover. DOI:10.25928/n8ac-y452.
[4] Kolditz, O., et al. (2012). OpenGeoSys: an open-source initiative for numerical simulation of thermo-hydro-mechanical/chemical (THM/C) processes in porous media. Environmental Earth Sciences 67 (2012): 589-599.
How to cite: Bittens, M. and Thiedau, J.: From Complexity to Comprehension: Interactive Real-Time Data Visualization for Geological Models and Uncertainty Analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9563, https://doi.org/10.5194/egusphere-egu25-9563, 2025.
Brittle damage commonly develops around tunnels in massive rocks under high-stress conditions. Understanding the shape and extent of the Excavation Damage Zone (EDZ) is crucial, particularly for deep geological repositories (DGRs) designed for nuclear waste storage. Within the EDZ, permeability often increases, which, in the context of nuclear waste disposal, could create preferential pathways for radionuclide migration. A comprehensive evaluation of brittle fracture formation over space and time necessitates the use of multidisciplinary monitoring systems. To facilitate such studies, a new Underground Research Laboratory (URL) has been recently developed in the Bedretto Underground lab for Geoenergies and Geosciences (BULGG) in southern Switzerland. This facility focuses on investigating the evolution of the Excavation Damage Zone (EDZ) in crystalline rocks. The experimental tunnel, which has been extended as a new branch tangential to the existing Bedretto tunnel, is equipped with a dense array of sensors installed prior to excavation. The main objectives of the PRECODE experiment are to understand: (1) short-term rock mass behavior and EDZ formation during tunneling; (2) long-term fracture propagation within the EDZ associated with environmental conditions (fluctuations in humidity and temperature); (3) permeability evolution around an open excavation and (4) the impact of tunneling on potential dislocations of nearby fault zones. In-situ data and a series of comprehensive laboratory tests provide a hydro-seismo-mechanically coupled reference data set for numerical simulations with the aim to further improve predictive models. This paper outlines the current status of the PRECODE tunnel and the short-term response of the tunnel to excavation. The development of stress-induced fractures was detected through acoustic emission (AE) monitoring during and after excavation. Brittle fracturing, in the form of spalling has been observed in the sidewall, where AE counts were concentrated. Borehole hydraulic and gas testing indicated a permeability enhancement in the close vicinity of the tunnel, attributed to the creation of new stress-induced fractures. The development of these fractures was further evidenced by borehole deformation monitoring using fiber optics.
How to cite: Hamdi, P., Dickmann, J., Kruszewski, M., Achtziger-Zupancic, P., Rinaldi, A., Villiger, L., Shakas, A., Bahrani, N., Perras, M., Wiemer, S., and Amann, F.: Short-Term Evolution of Excavation Damage Zone during PRECODE Mine-by Tunneling at BedrettoLab, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16953, https://doi.org/10.5194/egusphere-egu25-16953, 2025.
The assessment of deep geological repositories in crystalline rocks requires a thorough understanding of coupled hydro-mechanical (HM) processes. This is especially true for the rock mass in close proximity to the tunnel, in the so-called Excavation Damage Zone (EDZ), where coupled processes are at the highest intensity. During the drill-and-blast excavation of the 10-meter PRECODE experimental tunnel, a new branch of the Underground Research Laboratory (URL) located in the Bedretto tunnel in Southern Switzerland, distinct changes in pore pressure were registered. These pore pressure increases and decreases are expected to be dominated by an undrained poro-elastic response of the rock mass around the tunnel opening during excavation as well as dynamic forces caused by drilling and blasting operations. Using the finite element modeling software MOOSE and input parameters from extensive field campaigns measuring rock mass permeability and in situ stress conditions, we develop a three-dimensional numerical model that captures the HM response of the porous rock medium to the tunnel excavation. We validate model results against pore pressure data registered at several intervals within a borehole drilled and instrumented a few meters from the PRECODE tunnel. Additionally, we use strain data from the Distributed Strain Sensing (DSS) cable for model validation. Using results from the HM model calibrated against a comprehensive set of field measurements recorded during tunnel excavation, we evaluate the shape and extent of the short-term EDZ development around the tunnel.
How to cite: Kruszewski, M., Hamdi, P., Dickmann, J., Khaledi, K., Rinaldi, A. P., Wiemer, S., and Amann, F.: Modeling Coupled Hydro-Mechanical Effects during PRECODE Tunnel Excavation in Rotondo Granite, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18665, https://doi.org/10.5194/egusphere-egu25-18665, 2025.
As part of the programme for the development of a deep geological repository (DGR) for the disposal of radioactive waste in the Czech Republic, SÚRAO has provided support for research, development and demonstration activities at various underground research facilities for many years. SÚRAO’s research facility, the Bukov Underground Research Facility (URF), is located in the crystalline rock of the Bohemian Massif. This generic underground laboratory, which is used for the conducting of in-situ experiments and the testing of a range of methodological approaches, is situated on level 12 of the former Rožná I uranium mine, approximately 500 metres below the earth’s surface. The URF consists of two sections – Bukov URF I and URF II, both sections provide the critical infrastructure required for the testing of host rock, material testing and modelling methods and allow for the conducting of the research projects included in SÚRAO’s extensive experimental plan. The Bukov URF is critical in advancing the DGR project, supporting related scientific research, conducting experiments and, in the future, the performance of full-scale tests.
The Bukov URF research programme is based on seven defined key areas covering long-term monitoring, description of the rock environment, groundwater flow, engineered barriers for the DGR, effects of underground structures on the rock mass, construction technologies, and demonstration experiments. Currently, two major experiments are in operation at the URF I site will provide information that will enhance the understanding of the DGR engineered barriers and provide data for the long-term monitoring programme and the description of the rock environment. Completed projects considered groundwater flow and construction technologies, as well as some of the aforementioned research areas.
Experiments that focus on the development of the DGR engineered barrier system involve the use of bentonites from Czech deposits, e.g. BCV quarried at the Černý Vrch deposit, which comprises a calcium-magnesium material which is currently considered to be the Czech DGR reference material. Besides bentonite, the experiments are concerned with estimating the corrosion rates of the materials considered for the waste disposal package (e.g. carbon steel, which is being considered for the outer casing of the WDP, and copper as an alternative construction material).
The experiments that involve the research of BCV bentonite include subjecting the material to various conditions, such as artificial saturation and elevated temperatures (varying from 70°C up to 170°C), and the research of the influence of this bentonite on cement-based materials (to be used for the plugs of the DGR) and carbon steel. These experiments provide valuable information on the interactions that might occur within the bentonite itself and on how the bentonite will potentially influence other materials.
Future experiments will focus on the behaviour and characterisation of bentonite in the context of both small-scale and (near) full-scale projects. The experiments will focus on defining the behaviour of bentonite in solutions containing selected cations, the provision of information on the transfer of heat from the bentonite buffer into the host rock, and the study of the erosion of bentonite.
How to cite: Golubko, A.: Research and Development of the Engineered Barrier System for the DGR at the Bukov URF, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5615, https://doi.org/10.5194/egusphere-egu25-5615, 2025.
The Horonobe International Project (HIP) is an OECD NEA (Organisation for Economic Co-operation and Development - Nuclear Energy Agency) Joint Project running from February 2023 to March 2029. It includes 11 organisations from Asia, Australia, and Europe. HIP‘s main objectives are to 1) develop and demonstrate advanced technologies to be used in repository design, operation and closure, and a realistic safety assessment for deep geological disposal; and 2) encourage and train the next generation of engineers and researchers by sharing and transferring the knowledge and experience developed to date in the participating organisations.
HIP is conducted as a part of the Horonobe underground laboratory (URL) project in Horonobe town (northern Hokkaido, Japan). This project is in operation since 2001 in Neogene sedimentary rocks. It is a pure research and development laboratory (i.e., generic URL) for the final disposal of radioactive waste, which is not used as a final disposal site. HIP is divided into three main tasks:
Task A „Solute transport experiment with model testing“ develops realistic 3D solute transport models that can be applied to repository safety assessments for fractured porous sedimentary rocks. First in-situ (including tracer experiments) and laboratory experiments (diffusion and sorption experiments) provide basic characteristics of structures and processes relevant for solute transport. Based on these results, further in-situ experiments will validate and optimise the numerical and conceptual models for solute transport in fractured sedimentary rocks.
Task B „Systematic integration of repository technology options“ 1) develops and tests technology options for repository operation; 2) establishes the concepts and criteria for locating disposal pits or holes in suitable rock domains around the disposal tunnels; and 3) demonstrates the systematic integration of available technology options to arrange and construct the disposal pits or holes. Part of Task B is also the excavation of new galleries at 500 m depth including operational near-field exploration. So far, numerical models for the prediction of cracks, the inflow of groundwater and the development of the excavated damage zone have been developed.
Task C „Full-scale EBS dismantling experiment“ builds on the full-scale EBS (Engineered Barrier System) performance experiment for vertical emplacement, which has been carried out at the 350 m gallery since 2014. It aims to understand the thermal-hydrological-mechanical-chemical (THMC) coupled processes in such an EBS and to test and verify different THMC simulation codes based on monitoring data gained during the EBS experiment and its subsequent dismantling.
Results and experience of all above described tasks support the partnering institutions in the safety assessments for deep geological disposal of radioactive waste. In the context of the German site selection procedure for high-level radioactive waste, the results from HIP will support the further-developed preliminary safety analyses. The presentation will also highlight BGE's interests and contributions to the three tasks.
How to cite: Liebscher, A., Peti, L., Stockmann, M., Strusinska-Correia, A., Tatomir, A., Göbel, A., Ozaki, Y., Ohno, H., Tachi, Y., and Aoyagi, K.: Developing Advanced Technologies and Human Resources Towards Implementation of Geological Disposal: The Horonobe International Project (HIP), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14867, https://doi.org/10.5194/egusphere-egu25-14867, 2025.
Thermal loading significantly impacts the mechanical properties of mudstone, impacts which are crucial to understand for deep earth engineering applications such as geological disposal of radioactive waste, compressed air storage, geothermal energy, and underground coal gasification. This study analyses the response of Sidmouth Mudstone, part of the Mercia Mudstone Group, under triaxial compression with varied thermal loading conditions. Experiments were conducted at natural moisture contents across one and three thermal loading cycles to 90°C, with confining pressures of 5 MPa, at both 90°C and room temperature. The results indicate that under triaxial compression at 90°C, regardless of the number of thermal cycles, Sidmouth Mudstone exhibits a Poisson’s Ratio comparable to water and displays extremely brittle post-peak behaviour compared to room temperature conditions. After three thermal cycles at 90°C, the mudstone shows a higher fracture density. Triaxial strengths of 9 MPa and 24 MPa for tests at 90°C and room temperature, were recorded respectively. The primary mechanism driving the response is proposed to be thermal-hydro-mechanical coupling, where induced pore pressure from thermal expansion causes localised strain and propagating thermally induced fractures. This research contributes to understanding the response of mudstones under thermal loading and the magnitude of thermal-hydro-mechanical coupling effects.
How to cite: Norman, A., Ougier-Simonin, A., Valdez, R., Murphy, W., and Thomas, M.: Investigating Thermal-Hydro-Mechanical Coupling in Mudstones under Varied Thermal Cycles, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10497, https://doi.org/10.5194/egusphere-egu25-10497, 2025.
The HotBENT experiment is a joint undertaking of multiple international partners at the Grimsel Test Site operated by NAGRA [1,2]. It was designed to replicate the conditions that occur in a deep underground repository for high-level radioactive waste (see Figure 1). The experiment investigates the behaviour of bentonite buffer subjected to high heat loading (up to 200 °C) from the emplaced waste canisters and hydration from the surrounding host-rock. This gives rise to multiple processes, specifically within the bentonite buffer, that compete and interact in a complex way, including evaporation, induced desaturation and drying in regions affected by elevated temperatures, and conversely, saturation–induced swelling in the regions which are cooled. While the geometry of the experiment is not overly complex, it is not entirely straightforward due to the presence of multiple components, such as the heaters, bentonite buffer and underlying bases. Combined with the complex material behaviour also contribute to the intricate interaction of water and vapour transport and deformation processes, this introduces significant challenges. Consequently, predicting and assessing the long-term transient behaviour of this system, as observed throughout the HotBENT experiment remains challenging.
Fig. 1. The HotBENT experiment setup.
In this study conducted within the Benterest project, we present the results of our three-dimensional fully coupled thermo-hydraulic simulations of the HotBENT experiment using the computational open-source multi-physics platform OpenGeoSys [3]. Figures 2 and 3 depict the setup we use in the numerical modelling and a solution snapshot, respectively. Vapour diffusion, thermal and hydraulic conductivity, permeability, retention curve of bentonite, granite and concrete are shown to have a significant impact on the evolution of saturation (and desaturation), gas and water pressures. Herein, for the comparison and parameter calibration purposes, we employ the latest experimental data. We also discuss the numerical challenges associated with the parametrization and finite element discretization of the model.
Fig. 2. Numerical setup designated to interpret and simulate the HotBENT experiment (left), along with the prescribed temperature evolution of the heaters defined as Dirichlet boundary conditions (right).
Fig. 3. Simulation snapshot (when the target temperature of all heaters is reached) for the bentonite saturation pattern around the corresponding heaters and along the repository, as well as the spatial temperature distribution in the system.
Our findings will provide insights into the key factors influencing the bentonite buffer’s behaviour, contributing to the understanding of TH processes in engineered barriers under repository-like conditions.
References:
[1] https://grimsel.com/gts-projects/hotbent-high-temperature-effects-on-bentonite-buffers/hotbent-introduction
[2] F. Kober, R. Schneeberger, S. Vomvoris, S. Fensterle and B. Lanyon, HotBENT Experiment: objectives, design, emplacement and early transient evolution, Geoenergy, 1, 2023.
[3] https://www.opengeosys.org/
How to cite: Tatomir, A., Gerasimov, T., Simo, E., Burlaka, V., and Polster, M.: Thermo-Hydraulic Modelling of the In-Situ HotBENT Experiment: Investigating Bentonite Barrier Behaviour at High Temperature and Hydration, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10380, https://doi.org/10.5194/egusphere-egu25-10380, 2025.
The presented research project is aimed to simulate with simplistic, generic, numerical 2D models the linear elastic deformation of waste canisters in a rock salt matrix. It is based on own analogue models and an analytical solution (Mandal und Chakraborty 1990) for the linear elastic deformation behavior of pre- to syntectonic granitoid plutons intruding a schistose orogen. For this purpose, a numerical model consisting of a strong body in a weak matrix was deformed linear elastically in 2D under plain strain conditions. During deformation the Young’s modulus of the canister materials steel and copper was lowered and the Poisson’s ratio raised to simulate mechanical weakening of the canister while the rock salt matrix remained mechanically unchanged. Consequently, the canister became with time weaker than the surrounding rock salt matrix. The canisters were either empty or filled with steel in the model. Our results show clearly, that
- deformation gets more pronounced with increased mechanical weakening of the canisters,
- a copper canister develops a higher ellipticity than a steel canister and
- a strong, competent body in a weak, incompetent matrix shows different deformation patterns than a weak, incompetent body in a strong, competent matrix.
- In the first case (strong body in a weak matrix) concave strain and stress trajectories are observed plus material displacement towards the model margins.
- In the second case (incompetent body in competent matrix) material displacement from the model rims towards its center is observed and convex strain and stress trajectories occur.
Our simplistic, generic, numerical 2D models will help to strengthen our general comprehension of deformation processes in nuclear waste disposal systems.
References
Mandal, Nibir; Chakraborty, Chandan (1990): Strain fields and foliation trajecto-ries around pre-, syn-, and post-tectonic plutons in coaxially deformed terranes. In: Geol. J. 25 (1), S. 19–33. DOI: 10.1002/gj.3350250103.
How to cite: Dietl, C. and Rücker, C.: Numerical models concerning the deformation behavior of rigid bodies in a plastic matrix, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2172, https://doi.org/10.5194/egusphere-egu25-2172, 2025.
Compacted bentonite serves as an engineered barrier in deep geological repositories designed for confining high-level radioactive waste. Its role relies on maintaining a high swelling capacity to effectively seal the host rock fractures and limit radionuclide migration (Sellin & Leupin, 2013). However, groundwater flow can favor bentonite swelling and expansion through fractures in the crystalline host rock, leading to mass loss and potentially undermining the barrier's effectiveness. To ensure the safety of the repository, it is necessary to predict the long-term erosion of the bentonite barrier.
Laboratory-scale experiments simulating an artificial fracture were developed to study bentonite erosion and sedimentation in vertical fractures, focusing on parameters like clay type, water chemistry, flow and fracture aperture. To extend these findings, this research examined the impact of the groundwater flow velocity and direction in the erosion and sedimentation of compacted bentonite simulating the clay barrier in a fracture of a granitic formation.
The experimental setup consists on compacted bentonite (SWy-3, Wyoming) pre-equilibrated with sodium and compacted to a dry density of 1.4 g/cm³ (Alonso et al., 2019) emplaced in an artificial fracture of desired aperture (0.2 mm and 0.4 mm). A low-saline solution (10⁻³ M NaCl) is injected with peristaltic pumps, simulating the flow of groundwater at desired experimental velocities (3.5·10-7 m/s; 1.4·10-6 m/s and 2.1·10-6 m/s) and direction (upward, downward and lateral). Tests in the absence of flow were used as reference.
Over a 30-day period, the clay expanded into the fractures, and its progression was tracked through periodic photographs. At the end of the experiment, the amount of extruded and sedimented clay in the bottom of the fractured was collected and weighted, alongside the mobilized colloid generation by measuring their concentration and particle size using Photon Correlation Spectroscopy.
As soon as the bentonite was hydrated, expanded in the fracture with radial geometry. The expansion of bentonite ceased after 10 days, reaching similar maximum expansion distances for the three flow velocities and flow directions analyzed. Continuous flow promotes particle mobilization, as evidenced by a reduction in the radius of the expanded ring, which is more pronounced at higher flow velocities. However, in tests conducted at lower flow velocities, the behavior was comparable to that observed in the absence of flow. The comparison of test carried out at different flow directions suggested that flow can only mobilize the fraction of the initially expanded halo accessible to the flow, being lower the removal in the lateral direction compared to that upward or downward. These results suggest that, in clay barrier sedimentation processes, gravity plays a secondary role compared to factors like chemistry, flow velocity, duration, or fracture aperture.
REFERENCES
Alonso, U., Missana, T., Gutiérrez, M. G., Morejón, J., Mingarro, M., & Fernández, A. M. (2019). CIEMAT studies within POSKBAR project Bentonite expansion, sedimentation and erosion in artificial fractures (Technical Report TR-19-08). SKB.
Sellin, P., & Leupin, O. X. (2013). The Use of Clay as an Engineered Barrier in Radioactive-Waste Management – A Review. Clays and Clay Minerals, 61(6), 477–498. https://doi.org/10.1346/CCMN.2013.0610601
How to cite: Dieguez, M., Morejon, J., Mingarro, M., García-Gutiérrez, M., Missana, T., and Sellin, P.: Impact of flow velocity and direction on bentonite erosion and sedimentation in vertical fractures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20385, https://doi.org/10.5194/egusphere-egu25-20385, 2025.
An internationally accepted concept for the long-term containment of spent high-level nuclear waste (HLW) is its disposal using deep geological repositories. Therefore, the need arises to evaluate long-term safety and the efficiency of under-ground nuclear waste storage regarding among others radionuclide transport mechanisms. For this purpose, numerical modeling is an essential and powerful tool. This BGR contribution focuses on the performance assessment modeling of a generic nuclear repository in crystalline rock done within the framework of the DECOVALEX-2023 Task F joint project. The BGR-modeling strategy describes flow and transport in fractured crystalline rock using a combined Equivalent Continuous Porous Media (ECPM) and Discrete Fracture Network (DFN) approach. Using the open-source finite element code OpenGeoSys version 6, stationary flow and radionuclide transport is simulated based on the advection-dispersion equation.
Fractures and other types of discontinuities, which usually characterize crystalline rock, are expected to influence the hydraulic behavior of system and hence potentially influence transport mechanisms in the system. Therefore, their representation in numerical models is non-trivial. For this study, large connected fracture zones are represented as deterministic features. Meanwhile smaller fractures, in which only statistical characterization can be obtained, are stochastically generated and represented as an ECPM with upscaled hydraulic properties.
This contribution aims to propose an approach towards the performance assessment of a generic deep geological repository in fractured crystalline rock. Results regarding the obtained flow field as well as the corresponding radionuclide migration will be presented.
References
[1] Leone, R. et al., Comparison of performance assessment models and methods in crystalline rock: TASK F1 DECOVALEX-2023. Geomechanics for Energy and the Enviroment 2025; 41: 100629. https://doi.org/10.1016/j.gete.2024.100629.
How to cite: Guevara Morel, C. and Thiedau, J.: Numerical flow and transport modeling of a generic nuclear repository in crystalline rock, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15250, https://doi.org/10.5194/egusphere-egu25-15250, 2025.
Crystalline rocks are one of the potential host rocks for an engineered nuclear waste repository (NWR). However, crystalline rock formations contain extensive fracture networks, which are challenging to characterise hydrogeologically (Neuman, 1987). Thus, numerical models incorporate fracture networks and hydraulic heterogeneity in a statistical manner. Conventional discrete fracture network (DFN) models need to define the fracture’s orientation, aperture and roughness, which are themselves uncertain and challenging to characterise even at a laboratory scale (Neuman, 1987; Cvetkovic et al., 2004). Furthermore, field data on the hydraulic and transport properties of fracture networks remain rare (Neuman, 1987). To tackle this, geostatistical principles can be employed, approximating fractured rock mass permeability as a stochastic effective continuum permeability field (Neuman, 1987). To represent the important role of preferential pathways, subsequent probabilistic radionuclide (RN) transport studies are essential (Cvetkovic et al., 2004). The present study adopted the Gaussian autocovariance function to approximate fractured granitic rock permeability fields with log-normal distribution derived from semivariograms and simulated the transport of radionuclides (Neuman, 1987). The study considered a two-dimensional domain of an NWR consisting of buffer, intact granite rock and fractured granitic rock with multiple realisations of fractured rock permeability to account for uncertainty. The granitic rock’s correlation length, mean and standard deviation of permeability were derived from packer tests (Neuman, 1987). The transport mechanisms of the retarding and mobile radionuclides (Sr-90, Cs-135, I-129, Cl-36) considered were advection, diffusion, sorption and decay (Poller et al., 2004). The RN transport was simulated in the open-source finite element code OpenGeoSys (OGS) for one million years using the Monte-Carlo framework (Bilke et al., 2019). The simulations indicated that Sr-90 and Cs-135 sorbed onto the buffer due to their retarding nature and did not reach the geological barrier in significant concentrations. Besides, Sr-90 decayed faster due to its shorter half-life, whereas Cs-135 strongly sorbed onto the buffer due to its high retardation coefficient. However, the mobile radionuclides (I-129 and Cl-36) were transported into fractured rock mass. The mean and confidence intervals of mobile radionuclides within the crystalline rock were observed to be within the safe dosage limit of the biosphere. Overall, the study quantified the uncertainty in dosage rates, and the proposed framework reduced the computations of transport simulations in an NWR to a greater extent than traditional DFN models. Additional studies are essential to improve the computational efficiency for large-scale three-dimensional modelling, and an increased number of realisations to gain confidence.
How to cite: Bhukya, P. K., Wang, X., Nagel, T., and Arnepalli, D. N.: Monte-Carlo simulation of radionuclide migration from a nuclear waste repository in the fractured crystalline rock formation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2252, https://doi.org/10.5194/egusphere-egu25-2252, 2025.
Trajectory-based simulations of transport in porous and fractured media are computationally fast and straightforward to parallelize. They neither induce spurious oscillations nor do they introduce numerical dispersion. Such simulation techniques rely on consistent and mass-conservative particle tracking schemes posing an attractive alternative to traditional solutions via an Eulerian discretization of the transport equation possibly including chemical reactions or radioactive decay chains as well. An accurate simulation of many processes in geological media requires a coupled solution of fluid flow, heat transport, and mechanical deformation. Integrated simulation platforms like OpenGeoSys typically rely on the finite element method in different variations for solving the resulting coupled equation system. Reasons for this are the relative ease to implement the coupling of different physcial processes via finite elements, their ability to natively handle full material tensors and unstructured grids, the small number of degrees of freedom compared to other discretization techniques, as well as their matureness and common usage in solving problems from structural mechanics. However, finite element solutions of the transport equation may suffer from spurious oscillations or numerical diffusion, if grids and time-stepping are not appropriate. Particle-tracking circumvents these issues but relies on a consistent velocity field originating from the flow solution. While finite elements yield a continuous solution of the primary unknown and conserve mass in the nodes, unfortunately, they yield Darcy velocity fields in the elements which are neither conforming nor element-wise mass conservative leading to a jump of the Darcy velocity normal to an element interface. Such velocity fields do not meet the requirements for accurate and consistent particle tracking. To overcome this challenge, we adapted the flux projection of Selzer and Cirpka (2020), initially presented for steady-state groundwater flow on simplices, to coupled thermo-hydro-mechanical models based on the standard Galerkin finite element method on triangular prisms, thus yielding a conforming and element-wise mass-conservative Darcy velocity field via postprocessing. Based on this, we used the semi-analytical particle-tracking scheme presented by Selzer et al. (2021) to compute trajectories. We coupled this framework to OpenGeoSys, which is an open-source multi-field simulation platform based on finite elements, and applied it to a three-dimensional thermo-hydro-mechanical model including several geological layers simulating the fate of a conceptually simplified deep geological repository for high-level nuclear waste in clay stone as host-rock formation over one million years including the effects of glacial cycles.
How to cite: Selzer, P., Zill, F., Silbermann, C. B., Shao, H., and Kolditz, O.: Accurate and Consistent Lagrangian Transport Simulations for Finite-Element-Models of Thermo-Hydro-Mechanical Processes in Porous Media, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13190, https://doi.org/10.5194/egusphere-egu25-13190, 2025.
The Callovo-Oxfordian claystone, as potential host rock for the storage of radioactive waste in France (Bure, Meuse/Haute-Marne), is subjected to coupled processes, such as stress variations during excavation, changes in saturation, thermal variations caused by exothermic waste, and chemical interactions. To assess the feasability of geological storage in the short and long term, it is essential to develop coupled THMC (Thermo-Hydro-Mechanical-Chemical) models and experimental characterizations. These approaches, which are fundamental to geo-engineering applications, allow for a more precise understanding of associated risks.
This study focuses on evaluating the thermal effects on the mechanical behavior of Callovo-Oxfordian claystone through triaxial tests that simulate in-situ storage conditions. The tests are conducted in triaxial compression cells equipped with heating systems to examine the material at temperatures ranging from 20 to 90°C. Deformations are measured using strain gauges. Our experiments are focusing on the influence of parameters such as confining pressure (4, 8, 12 MPa), temperature (20, 45, 70, and 90°C) and orientation (parallel and perpendicular to the bedding plane). To reduce data dispersion, all tests are conducted on cores extracted from the same borehole, ensuring a homogeneous calcite content (approximately 20%) and particular attention is given to the initial saturation degree of the samples. Each sample undergoes preliminary 2D X-ray imaging to visually evaluate initial cracks. This step is critical for selecting the least initially damaged samples, thereby reducing biases caused by pre-existing microcracks. Only the samples with minimal cracks are further scanned in 3D, both before testing (initial state) and after testing (final state). These scans are analyzed with VGStudio MAX software (Volume Graphics GmbH) to evaluate deformation mechanisms occurring during deformation.
Our tests reveal that, for both orientations (parallel and perpendicular), the heating phase generates an overpressure of interstitial water (due to thermal expansion), likely inducing microcracks parallel to the bedding planes. This results in a slight reduction of the peak strength of the Callovo-Oxfordian claystone, which increase with increasing temperature due to thermo-hydro-mechanical damage caused by heating. Furthermore, regardless of orientation or confining pressure, an increase in the heating rate enhances the decrease in peak strength.
This research is essential for understanding the impact of heating on the mechanical properties of the host rock in order to optimise the design of the disposal and improve its long-term safety.
How to cite: Abou Chakra, B., Grgic, D., Bonnelye, A., and De Lesquen, C.: Effect of temperature on the mechanical behavior of Callovo-Oxfordian claystone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4435, https://doi.org/10.5194/egusphere-egu25-4435, 2025.
This study assessed the hydrogeological properties of the deep geological environment to develop safety criteria for the natural barriers used in the deep geological disposal of high-level radioactive waste in Korea. The assessment focused on the distribution and trends of hydraulic conductivity and permeability properties appropriate for the domestic geological environment, using various in-situ hydraulic test data collected for groundwater development and management. To develop a depth-hydrogeological property relationship model suitable for domestic conditions, the study reviewed various international research examples and applied a representative model that explains the trends of hydraulic conductivity and permeability with depth. The development of the model suitable for Korea involved applying ensemble regression analysis to account for the uncertainty of various factors in the collected data. The results confirmed that existing international depth- hydrogeological property relationship models adequately describe the characteristics of the domestic geological environment. Considering the preferred hydrogeological criteria suggested by countries like Sweden, Germany, and Canada, there is a high likelihood that a suitable geological environment exists in Korea. Additionally, the application of hydrogeological criteria indicative of low-permeability environments showed that suitable conditions for disposal construction increase at depths greater than 300 m, where the influence of fractures on groundwater flow might be minimal at depths exceeding 500 m. This research can serve as foundational information for establishing hydrogeological safety standards for natural barriers in Korea according to international regulatory guidelines.
How to cite: So, S., Kim, S., and Jeong, J.: Evaluation of Hydrogeological Characteristic of Natural Barrier in Korea for Establishing Safety Guidelines of Deep Geological High-Level Radioactive Waste Disposal Site, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5519, https://doi.org/10.5194/egusphere-egu25-5519, 2025.
Long-term safety analyses need to be performed by the implementer to identify adequate siting regions in the course of the site selection process in Germany, regulated by the Site Selection Act (Standortauswahlgesetz - StandAG). The Federal Office for the Safety of Nuclear Waste Management (Bundesamt für die Sicherheit der nuklearen Entsorgung - BASE) as responsible federal authority has to review the implementer’s long-term safety analyses. To perform this duty at the required detailedness, and to identify potentially missing processes, it will be necessary to recalculate important aspects of the analyses by means of numerical computer programs. In addition, this will allow to assess the underlying uncertainties of the implementer’s long-term safety analyses from a regulatory point of view.
Numerical modelling requires a high degree of quality assurance. Therefore, simplified physical problems are needed to check the results of the computer programs against analytical solution of these problems or to assess the plausibility of the results.
At the BASE it is planned to further develop and use the open source programs PFLOTRAN [1] and FEHM [2] for the review of long-term safety analyses. PFLOTRAN is an open source, multi-phase flow and reactive transport simulator designed to leverage massively-parallel high-performance computing to simulate subsurface earth system processes. FEHM is used to simulate reactive groundwater and contaminant flow and transport in deep and shallow, fractured and unfractured porous media and allows for a coupling of the transport processes with geomechanical processes. In addition, the BASE develops its own multi-phase flow and transport program MARNIE2 [3] which allows flow and transport calculations including processes which are relevant in long-term safety analyses.
This contribution presents examples from the newly developed regression test procedure for MARNIE2 which allows to check plausibility and functionality of fundamental processes in the code when the source code undergoes changes due to code development. To compare the computer programs among each other a comparison with the analytic solution for the advective and diffusive transport of a radionuclide chain with four members including adsorption is presented. As an example for recent code development, first results for the compaction of salt backfill in PFLOTRAN are presented. Here, the further development of PFLOTRAN is motivated by the participation of the BASE in the task “performance assessment” of the DECOVALEX 2027 initiative.
Literature
[1] Nole, G.D. Beskardes, D. Fukuyama, R.C. Leone, H.D. Park, M. Paul, A. Salazar, G.E. Hammond and P.C. Lichtner: Recent Advancements in PFLOTRAN Development for the GDSA Framework (FY2023), SAND2023-07655, (SNL-NM), United States, 2023; and references therein.
[2] Zyvoloski: FEHM: A control volume finite element code for simulating subsurface multi-phase multi-fluid heat and mass transfer. Earth and Environmental Sciences Division, Los Alamos National Laboratory, LAUR-07-3359, 2007.
[3] Navarro, T. Beuth, G. Bracke, J. Eckel, G. Frieling, S. Hotzel, I. Kock, H. Seher, and T. Weyand: Weiterentwicklung und Qualitätssicherung von Modellierungswerkzeugen zur Durchführung und Bewertung von Sicherheitsanalysen im Standortauswahlverfahren, Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH, GRS-622: Köln, Februar 2021.
How to cite: Eckel, J.: Code development and verification for the review of long-term safety analyses, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8501, https://doi.org/10.5194/egusphere-egu25-8501, 2025.
The Federal Company for Radioactive Waste Disposal (BGE) is responsible for identifying the site with the best-possible safety for the disposal of high-level radioactive waste for at least one million years in Germany. The Site Selection Procedure consists of three phases with an increasing level of detail. The first step of the first phase was completed in September 2020. Ninety sub-areas were identified that are expected to have favorable geological conditions for safe disposal. The potentially suitable sub-areas cover approximately 54% of Germany and are located in three different host rocks: rock salt (halite), claystone, and crystalline rock.
The second step of phase one is currently in progress and includes the so-called representative preliminary safety assessments. Within the preliminary safety assessments, the behavior of the disposal system is analyzed in its entirety, across all operational phases of the repository and under consideration of possible future evolutions of the disposal system with regard to the safe containment of the radioactive waste. The actual behavior of the repository system cannot be predicted for the entire assessment period of one million years. Therefore, the evolution of the repository system is derived systematically to ensure that the actual future evolution of the repository is covered.
This contribution presents the methodology and technical implementation for the systematic derivation of a limited number of expected and deviating future evolutions of the potential repository siting areas. Evolutions are derived from the analysis of FEP catalogues (features, events, and processes), which are comprehensive, structured descriptions of a repository system and the existing interactions and dependencies of processes and components within. In order to apply this work-intensive method to the ninety sub-areas under consideration, a basic FEP catalogue is compiled first, from which host rock-specific and area-specific FEP catalogues are created. An analysis of component and process interactions is completed at host-rock level and then transferred and adapted to individual areas, taking site-specific information into account.
To facilitate the documentation and analysis of the disposal system and ensure consistency, a sophisticated in-house database solution has been developed. The properties of the FEP-catalogue components and their relationships are mapped and respectively stored in a relational database. The application is accessible through a user-friendly web application. This approach guarantees data integrity, reproducibility, and usability and accelerates the evaluation process by employing automation where applicable.
How to cite: Rühaak, W., Müller, P., Schöne, F., Wengorsch, T., Gottron, E.-M., and Bartetzko, A.: Application of a database to manage multilevel area-specific FEP catalogues to identify a site for high-level radioactive waste disposal in Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8821, https://doi.org/10.5194/egusphere-egu25-8821, 2025.
Radioactive waste repository authority (SÚRAO) is responsible for the safe disposal of radioactive waste in the Czech Republic in accordance with the requirements of nuclear safety and environmental protection. SÚRAO currently operates low- and intermediate-level waste repositories Bratrství in Jáchymov (a former uranium mine), Richard (a discontinued limestone mine), and Dukovany (located on the premises of a nuclear power plant). Globally, deep geological repositories (DGR) are regarded as the safest solution for high-level waste and spent nuclear fuel, , Janoch, Hrádek, and Horka. The final site will be determined through a multicriteria evaluation, with an emphasis on favorable geological conditions. To support this decision, SÚRAO, in collaboration with its partners and contractors, is conducting one of the largest geological investigations in Czech history, aiming to finalize the site selection by 2030.
Generally, there are 3 main host rock types for DGR; sedimentary, crystalline and salt. Czech Republic decided to adapt crystalline host rock concept base on the rock type composition of region. All sites are situated within Bohemian massif unit, comprised mostly of variscian methamorpohsed rocks with numerous plutonic intrusions. The westernmost site is Březový potok, belonging to Central Bohemian Pluton. The site is formed by granodiorites intrusion into the older moldanubian unit ca. 346 Ma. Janoch is located within monotonous moldanubian subunit, part of moldabian unit. It comprises of paragneiss ca 340 Ma old. Hrádek mostly consists of granites (Eisgarn type) belonging to moldanubian plutonic complex. Horka sites sits within Třebíč pluton complex formed by K- and Mg-rich melanocratic microsyenite, commonly known as “Durbachite” which intruded into the older moldanubian rocks ca. 340 Ma.
While geological investigations have been ongoing throughout the site selection process, current efforts focus on obtaining detailed data at depths of 500 meters, the projected depth for the Czech DGR. Advanced geophysical methods, capable of delineating geological structures at depths of up to 1,000 meters, are critical to this process. Extensive drilling campaigns are planned at each site, involving multiple boreholes targeting depths of 300, 600, and 1,200 meters. Each borehole is planned to produce oriented drill cores and carry on comprehensive borehole testing, designed to verify crucial geological features above, at, and below the intended DGR depth. In addition to drilling, complementary research activities, such as detailed geological mapping and monitoring, are ongoing. These combined methods aim to construct comprehensive 3D geological models for each potential site. These models will serve as the cornerstone for the final site selection process in 2030.
How to cite: Klištinec, J., Mareda, L., and Dohnálkova, M.: Geological characterization of 4 potential sites for siting of the deep geological repository in the Czech Republic., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9129, https://doi.org/10.5194/egusphere-egu25-9129, 2025.
The internationally preferred option for the final disposal of High Level Nuclear Waste (HLNW) is the Deep Geological Repository. This solution in some cases, like the Spanish one, involves the use of an engineering barrier composed of compacted bentonite. The generation and accumulation of gases are a significant concern for the long-term performance of the clay-based barrier.
The FEBEX bentonite is the Spanish reference barrier material for the Engineering Barrier System (EBS). This material is a granulated bentonite (GB), composed predominantly of montmorillonite (>90%) with a maximum grain size of 5 mm.
The main aim of this study was to determine the gas breakthrough (BT) pressure on saturated samples under different conditions of compaction: dry density (1.5, 1.6 and 1.7 Mg·m-3), water content (14%, 22% and 26%), grain size distribution, and length/diameter (L/D) ratio of the cell (diameter 38 and 50 mm, length 20 mm).
Two types of custom-built equipment were used to generate de BT episodes and the detailed pressure-time data series. For the lower dry density values (1.5 and 1.6 Mg·m-3) gas-flow was calculated from dynamic fall-out tests (with variable injection and backpressures). For the highest dry density (1.7 Mg·m-3), gas flow was directly measured by mass-flowmeters in a high-pressure steady-state gas permeability unit (with steady injection pressure and atmospheric backpressure).
Before gas injection in each phase, samples were saturated and their hydraulic conductivity was measured. Average values of hydraulic conductivity, before and after the gas injection phase, were similar (0.1 – 8.5) 10-21 m2, indicating no major effect of gas injection on this property. After gas testing the samples were resaturated and the BT testing was repeated.
The BT pressure increased with higher dry density of the samples, higher water content at compaction and the decrease in the L/D ratio. Overall, there was a systematic repetition of the values of BT pressure in the same sample after resaturation, but the shape of the pressure-time series was different depending on the real BT value versus the injection gas pressure.
To study the effect of gas transport on macro-mesostructure (>7 nm) mercury intrusion porosimetry (MIP) analyses were performed after testing to compare with similar untested samples and study the evolution of pore size distribution during BT. Subsamples were taken in each bentonite sample close to the gas inlet and outlet zones, but no significant differences were observed between them.
How to cite: Garcia-Herrera, G., Martín, P. L., and Villar, M. V.: Gas breakthrough pressure of FEBEX bentonite compacted under different conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9496, https://doi.org/10.5194/egusphere-egu25-9496, 2025.
As part of the ThORN project [1], an in-situ experiment to quantify thermo-osmotic (TO) flow in Callovo-Oxfordian clays will be carried out at the Bure Underground Research Laboratory (URL) in Meuse/Haute-Marne, France.
While previous research on TO has been carried out on reconstructed samples, our in-situ experiment will be accompanied by the evaluation of well-controlled laboratory experiments on intact samples. The aim of this project is to quantitatively assess the importance and parameterisation of TO flow in clay under thermal gradients induced by the heat of nuclear decay. The design and evaluation of all experiments will be supported by numerical simulations in OpenGeoSys. The resulting models will be used to analyse near and far field effects in a repository environment.
This paper presents highlights of the preliminary design phase. Objectives, expectations and potential challenges are outlined and discussed. Predictive simulations of different designs and assumptions used in the design phase are presented and compared. We show how numerical simulations can be used to explore the potential results of physical experiments before they are built, and how this can optimise the workflow of the experiment.
References
[1] ThORN " Experimental investigations on thermo-osmotic flow in argillaceous materials relevant to deep geological repositories for radioactive waste " The Federal Office for the Safety of Nuclear Waste Management (BASE); Funds FKZ 4723F00104
How to cite: Kiszkurno, F., Magri, F., de la Vaissiere, R., Talandier, J., Robinet, J.-C., Plua, C., Armand, G., Geboreau, S., Dizier, A., Flood-Page, G., and Nagel, T.: ThORN - Experimental investigation of the relevance of thermo-osmotic flow in clay for radioactive waste disposal, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9943, https://doi.org/10.5194/egusphere-egu25-9943, 2025.
In finite element analysis (FEA) of deformation problems, volumetric locking is a common issue in nearly incompressible materials. Standard low-order elements (such as linear quadrilaterals or hexahedra) can become overly stiff under volumetric constraints, leading to inaccurate deformation predictions, checkerboard patterns in stress distributions, or, in some cases, divergence. Several methods are commonly used to address this issue, including selective reduced integration (e.g., the B-bar method and the F-bar method), mixed formulations, enhanced assumed strain (EAS) methods, higher-order elements, and polygonal/polyhedral elements. The F-bar method is specifically designed for large deformation problems and typically employs the incremental formulations of FEM for finite strain. This study derives an F-bar method for the total Lagrangian formulation. The derived linearized discretized weak form of the momentum balance equation resembles that of the B-bar method, adopting a concise and compact form. The proposed algorithms are verified using several classic large deformation examples, which exhibit volumetric locking in solutions obtained with standard FEA.
How to cite: Zill, F., Wang, W., Naumov, D., Kolditz, O., and Nagel, T.: Investigating the F-bar method as a remedy for volumetric locking in Finite Element Analysis with the total Lagrange formulation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10307, https://doi.org/10.5194/egusphere-egu25-10307, 2025.
This study explores the quantification of uncertainties in integrity assessments of geological barriers in repository systems, which is a crucial aspect required by German law (§5 Endlagersicherheitsanforderungsverordnung (EndlSiAnfV)). The analysis includes numerical approximations of thermally-hydraulically-mechanically coupled processes. The legal framework necessitates documentation of the impact of uncertainties on safety-oriented evaluations, thereby requiring a systematic investigation of uncertainties in simulated results from integrity analyses.
The German Federal Institute for Geosciences and Natural Resources (BGR) has been engaged in various projects such as ANSICHT-II, MeQUR, and ThermoBase to address the forward propagation of input parameter uncertainties through numerical approximations and have collectively contributed to developing methods for quantifying uncertainties related to repository systems.
The study focuses on quantifying uncertainty within two primary steps: sensitivity analyses and stochastic modeling. Sensitivity analyses are employed first to identify the significance of each individual input parameter in a numerical simulation, as it is likely that uncertainty in many parameters may have negligible effects on the integrity of the containment providing rock zone (CRZ). The result is a set of essential input parameters that are then used in the second step to make quantitative statements about the stochastic state space, which is sampled using methods like Monte-Carlo sampling or stochastic collocation.
In the project ANSICHT, criteria were developed based on the EndlSiAnfV to indicate integrity within the CRZ in clay rock. These criteria can be represented as functions. For stochastic models, these functional dependences are expanded to include all parameters in the state space, known as stochastic dimensions. Methods for stochastic post-processing have been developed that allow for analysis without any prior data reduction.
The study also highlights the development of specialized software tailored to handle the computational demands associated with uncertainty quantification in numerical integrity analyses for repository systems. This includes the OpenGeoSys Uncertainty Quantification framework (OpenGeoSysUncertaintyQuantification.jl) developed by BGR, which has been published in the Julia programming language (Bittens, 2024).
Additionally, an interactive dashboard is presented that provides intuitive visual access to the results and can thus contribute to knowledge transfer about safety-relevant processes in the repository and the underlying uncertainties.
Bittens, M. (2024). OpenGeoSysUncertaintyQuantification.jl: a Julia library implementing an uncertainty quantification toolbox for OpenGeoSys. Journal of Open Source Software, 9(98), 6725.
How to cite: Maßmann, J., Bittens, M., and Thiedau, J.: Uncertainty Quantification and Visualization Techniques for Numerical Integrity Analyses, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10540, https://doi.org/10.5194/egusphere-egu25-10540, 2025.
Preliminary safety analyses are part of the site selection procedure for a repository of heat-generating radioactive waste in Germany. The Federal Company for Radioactive Waste Disposal (BGE) is conducting representative preliminary safety analyses for defined potential sub-areas. The assessment of the long-term safety of potential repository systems for heat-generating waste in these areas requires knowledge of the temperature field as the initial temperature of the host rocks is crucial for determining the repository design and for analysing expected future developments with regard to the safe containment of radionuclids. In the joint research project ThermoBase commissioned by the BGE, the GFZ Helmholtz Centre for Geosciences (GFZ) and the Federal Institute for Geosciences and Natural Resources (BGR) focus on the temperature distribution in areas with sedimentary host rocks of rock salt and claystone. The present day temperature field in the subsurface can be described on the basis of borehole observations supplemented by numerical temperature models. This approach is subject to significant uncertainty in areas with structural differentiation and low data density. Therefore, structural and thermal data must be determined, and uncertainties in thermal property variations and thermal boundary conditions must be considered, to adequately represent the host rocks in the models.
To better characterize the temperature distribution in the sub-areas, 3D finite element meshes are being developed by the GFZ to represent the geological structure in great detail. Thermal properties of host rocks are being measured in the laboratory and derived from high-resolution geophysical and temperature logs, ensuring accurate parameterization of the models. Transient temperature boundary conditions are incorporated into the simulations to account for past climate variations, such as glacial and interglacial cycles, influencing the current temperature field. First results, like heat flow calculations and temperature maps for depths of interest, offering insights into the spatial variability of the thermal field and its implications for repository planning.
The BGR uses generic geological models to conduct statistical numerical analyses on the effect of parameter variations on the temperature distribution for typical geological situations with sedimentary host rocks. Subsequently, a heat-generating term representing the heat introduced by a repository is included in the models, and the impact of uncertainties in input parameters on the safety-relevant temperature development in the repository area is assessed. Additionally, we provide insights into the minor effects of permafrost during potential future cold phases.
How to cite: Noack, V., Bittens, M., Maßmann, J., Frenzel, B., Frick, M., Norden, B., Salis Gross, E., Deon, F., and Fuchs, S.: Thermal-geological data for preliminary safety analyses of repository systems in German sedimentary host rocks – new results of the project ThermoBase, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10982, https://doi.org/10.5194/egusphere-egu25-10982, 2025.
A systematic benchmark suite is conducted to evaluate numerical methods in hydro-mechanical (HM) fracture mechanics. These benchmarks draw inspiration from experimental data collected using the GREAT cell at the University of Edinburgh—an advanced equipment designed to analyze fractured rocks under rotating stress conditions that simulate real-world subsurface environments. Given the inherent complexity of the GREAT cell experiments, the benchmarks have been simplified to replicate key behaviors while remaining manageable for computational modeling. This approach allows researchers to assess and compare numerical methods for simulating fracture propagation and hydro-mechanical interactions.
Two numerical approaches were utilized to perform these simulations: the variational phase field (VPF) method and the lower interface element (LIE) method. The VPF method employs a diffuse fracture representation, which enables it to model dynamic fracture propagation like branching and merging without the need for predefined paths. In contrast, the LIE method uses a discrete fracture representation, where fractures are explicitly embedded as interfaces within the computational mesh. While the LIE method is computationally efficient for stationary or pre-existing fractures, it lacks the inherent capability to simulate propagating fractures. By comparing these complementary approaches, the study highlights their respective strengths and limitations, providing valuable insights into fracture behavior under diverse hydro-mechanical conditions.
All numerical implementations and benchmarks are available in the OpenGeoSys platform, ensuring accessibility and reproducibility. This research contributes to the DECOVALEX 2027 providing tools for robust numerical code evaluation.
How to cite: Mollaali, M., Wang, W., You, T., Yoshioka, K., and Kolditz, O.: Numerical benchmarking of GREAT cell experiments: insights into the impact of polyaxial stresses on fluid flow in fractured rock, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13137, https://doi.org/10.5194/egusphere-egu25-13137, 2025.
The assessment of the long-term performance of the engineered barrier system (EBS) of a high-level radioactive waste (HLW) deep geological repository requires the use of high-fidelity reactive transport models. The EBS in a HLW repository includes: the canister, the compacted bentonite buffer and the concrete liner. Artificial intelligence and machine learning methods (ML) are growing at a very fast pace and have been used for: a) Accelerating numerical simulations, b) Addressing multiscale and multiphysics couplings, and c) Uncertainty quantification and sensitivity analyses. Here we present high-fidelity models and ML methods to simulate steel canister corrosion, corrosion products and their interactions with compacted bentonite. Metamodels and surrogate models provide approximate and efficient solutions which emulate the high-fidelity reactive transport simulations and can reduce significantly the CPU times. The high-fidelity model was calibrated with data from the FeMo corrosion test performed by CIEMAT/UAM under isothermal and saturated conditions for 15 years. The FeMo test consists of 6 stainless-steel sinters surrounded by Fe powder emplaced in holes drilled in a FEBEX bentonite block. The bentonite block was hydrated with granitic water through the sinters by using 6 syringes. Two different particle sizes (64 and 450 µm) were used in Fe powder of the FeMo tests. Model results show that pH increases to 9.5 and magnetite is the main corrosion product. Siderite, greenalite and saponite-Mg also precipitate at the Fe powder/bentonite interface. A metamodel has been developed for a geochemical system with interactions of steel/bentonite and precipitation of corrosion products. The system includes 3 primary dissolved species (Fe2+, H+ and O2aq), 2 aqueous complexes (OH- and H2aq) and magnetite. A set of 5000 data were sampled with a Latin Hyper Cube (LHC) sequence. Batch simulations were performed with CORE2Dv5 for 5000 data with the following 3 inputs: Fe, H and O2. Outputs include aqueous primary concentrations, aqueous secondary concentrations, magnetite, pH and Eh. The metamodel is based on Gaussian Processes and Random Forests for defining two groups corresponding to pH > 9 and pH ≤ 9. The metamodel provides excellent results for most of the output variables. Working with log for concentrations of H+, OH- and O2 improves significantly the results for H and O2. When the metamodel is trained by working with concentrations of dissolved Fe, the validation results show some negative concentrations. On the other hand, when the metamodel is trained by working with the logarithm of the concentrations of dissolved Fe, the predicted validation concentrations are always positive, but the metrics of the validation are slightly worse. The accuracy of the metamodel is significantly improved for pH by defining two groups, one for pH ≤ 9 and another for pH > 9.
Acknowledgements: This research was funded by ENRESA within Work Package ACED of EURAD (Grant Agreement nº 847593), within WP HERMES of EURAD-2 (Grant Agreement nº 101166718) and Project PID2023-153202OB-I00 funded by Spanish Ministry of Science and Innovation We acknowledge the contributions of CIEMAT and UAM who performed FeMo tests and provided the experimental data.
How to cite: Mon, A., Samper-Calvete, J., Montenegro, L., Samper-Pilar, J., Yang, C., and García, E.: High-fidelity coupled reactive transport models and metamodels of porewater chemistry, solute transport and geochemical evolution interactions in the engineered barrier and the steel canister in a HLW repository, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19304, https://doi.org/10.5194/egusphere-egu25-19304, 2025.
