ERE3.3 | Deep Geological Repositories – characterization of barrier materials assessment of barrier integrity and regulatory lessons learnt
EDI
Deep Geological Repositories – characterization of barrier materials assessment of barrier integrity and regulatory lessons learnt
Convener: Thomas Nagel | Co-conveners: Fabien Magri, Jobst Maßmann, Vaclava Havlova, Axel Liebscher, Klaus-Jürgen Röhlig
Orals
| Tue, 16 Apr, 10:45–12:30 (CEST), 14:00–15:45 (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, 10:45
Tue, 16:15
The successful implementation of safe deep geological disposal of nuclear waste and other long-lived waste is one of the currently most pressing environmental challenges in several countries worldwide. Site investigation and selection are primarily geoscientific tasks that require interdisciplinary collaboration of different disciplines, like geophysics, hydrogeology, (hydro-)geochemistry, mineralogy, geomechanics, material science, and geological as well as THMC modelling. The geoscientific information will then, together with other lines of evidence, be used in order to investigate performance and safety of disposal facilities.

As is the case for other subsurface technologies, barrier integrity is a crucial aspect for such assessment of nuclear waste disposal. Numerical simulations, in conjunction with experimental studies are an integral part of safety and environmental-impact assessment concepts. Reliable comparative analyses of potential technological options require coupled THMC models capturing the particularities of each rock type and associated repository concept. Structural as well as process complexity are often met by data scarcity and variability, necessitating the treatment of uncertainties and variability.
The session provides a platform for the exchange on the following topics.
- The THMC characterization of materials in natural or engineered barriers in lab- or field-scale experiments
- Hydro-mechanical behaviour of materials with extreme hydraulic properties (e.g. low permeability, high suction) and ranging from ductile viscopolastic salt rocks to quasibrittle fractured rock masses
- Hydraulic and chemical behaviour of geologic and geotechnical barriers
- Computational methods, models and uncertainty quantification for barrier integrity assessment in the multi-barrier system
- Geotechnical aspects of repository construction, operation, and post-closure, such as monitoring methods, excavation and support, retrieval/recovery, etc.
- The minimally invasive characterization of geology and underground installations using geophysical and geohydrological methods
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.

This session is organized as part of the DGR series, cf. ERE 3.x and ERE3.X

Orals: Tue, 16 Apr | Room K2

10:45–10:50
Site selection
10:50–11:00
|
EGU24-13377
|
ERE3.3
|
solicited
|
Highlight
|
On-site presentation
Boris Faybishenko, Jens Birkholzer, LianGe Zheng, David Sassani, and Emily Stein

More than 50 countries worldwide are currently exploring options for radioactive waste (RW) disposal, considering the link between geoscience fundamentals and the safety of RW disposal sites. The presentation will focus on the lessons learned from representative RW disposal projects worldwide (such as those conducted in Sweden, Finland, France, Spain, Switzerland, Japan, and the USA), summarizing the existing deep geological repository (DGR) concepts, including potential DGR site selection and characterization, as well as long-time modeling predictions. A comparative assessment of models of coupled thermo-hydro-mechanical-chemical (THMC) processes has been performed within the scope of the international project DECOVALEX, which has helped advance the understanding of THMC processes in geological systems. The experimental and modeling studies of the DGR concepts are ultimately linked to assessing the safety of RW disposal. The presentation will provide critical references and case studies related to the representative national disposal programs, which would interest geoscientists, engineers, and decision-makers working on national RW disposal programs. We will summarize and compare challenging geological problems and experiences in siting nuclear waste repositories in different host rocks, such as hard rock (crystalline and sediments), clayey, and salt formations. The availability of rock in a country limits the choice of rock type for the DGR. The interplay of geological conditions with technical feasibility, an engineering design for different rock types and operational and post-closure safety is critical in technical evaluating potential sites. We will also present summaries of the progress in international cooperation studies and testing of the design of buffer and backfill materials, the development of the concept of RW disposal in deep boreholes, the R&D research in Underground Research Laboratories (URL), and multi-national RW repository initiatives. 

Acknowledgments: LBNL work was supported under Contract Number DE-AC02-05CH11231 with the US DOE. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

 

How to cite: Faybishenko, B., Birkholzer, J., Zheng, L., Sassani, D., and Stein, E.: International Concepts for the Assessment of Deep Geological Disposal of Radioactive Waste, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13377, https://doi.org/10.5194/egusphere-egu24-13377, 2024.

11:00–11:10
|
EGU24-6514
|
ERE3.3
|
Highlight
|
Virtual presentation
|
Thomas Flüeler

Dealing with a complex sociotechnical system such as radioactive waste disposal needs an integrated perspective. Much of the widespread blockage faced hitherto may be ascribed to the neglect of relevant dimensions involved. Normatively, the principle of sustainability (incorporating passive protection and control) suggests itself as a reference system. It facilitates a stepwise analysis of dimensions: not only the conventional triad of ecological, economical, and social but also temporal, spatial, technical, political, and ethical. It forces upon stakeholders, including decision makers, an examination of these dimensions and is apt to incorporate most parties’ perspectives, needs, goals, and knowledge systems. After all, we need safe as well as acceptable and accepted sites with facilities designed, built, operated and sustainably closed in due time.

Long-term management of highly toxic waste epitomises three central distributional issues: - local cost and risk vs. general benefit (intragenerational equity issue), - lay persons’ vs. experts’ perspectives (evidentiary equity), - today’s vs. future generations (intergenerational equity). The long-term (ecological) waste dimension is of outstanding ethical relevance: The ones who make the profit (e.g., energy incurring waste) most likely do not bear – possible – risks from the waste. Still, the current generations (we!) have to decide (postponement is also a decision), and: Apart of winners (this waste producing society) there will be losers (locals and future generations). A formidable risk-benefit asymmetry.

Against this background, it is not surprising that North’s statement of over two decades ago is still valid: High-level nuclear waste management “has the deserved reputation as one of the most intractable policy issues facing the United States and other nations using nuclear reactors for electric power generation” (North 1999, 751).

In view of a common understanding to reach a “solution”, it is vital to explore contextual issues and tacit/implicit knowledge – they determine the degree of societal understanding of the eventual disposition system. It is useful to specify what may be “common ground”. Trying to decompose ever-used buzzwords like “consensus” or “compromise” one may outline where and how “common ground” is likely to be achieved. We cannot assume to reach consensus “at heart”, in the stakeholders’ core beliefs. Society must, however, agree on three levels: 1. Problem recognition: The waste exists, the problem must be “solved”, at least set on track to be solved; 2. Main goal consensus: The degree of protection and intervention must be defined; according to the scientific consent, passive safety must prevail; 3. Procedural strategy: The “rules of the game” (to find a suitable site and to implement disposal) have to be clear from the outset.

The present proposal (Flüeler 2023) avoids an undue complexity reduction and a decontextualised “technical fix” or, for that matter, “social fix” (with volunteering communities in the forefront). It is based on a thorough comparison of national waste programmes.

____________________

North, D.W. 1999. A perspective on nuclear waste. Risk Analysis. 19/4. 751-758. https://doi.org/10.1111/j.1539-6924.1999.tb00444.x.

Flüeler, T. 2023. Governance of radioactive waste, special waste and carbon storage. Literacy in dealing with long-term controversial sociotechnical issues. Springer Nature Switzerland, Cham. 145 pp. https://doi.org/10.1007/978-3-031-03902-7.

How to cite: Flüeler, T.: Lessons from national approaches. A long uphill struggle in search of sites for nuclear waste repositories, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6514, https://doi.org/10.5194/egusphere-egu24-6514, 2024.

11:10–11:20
|
EGU24-14424
|
ERE3.3
|
Highlight
|
On-site presentation
Susanne Schneider, Harriet Kause-Berg, and Florian Baasch

In Germany disposal of low- and intermediate level radioactive waste is intended and took place in deep geological repositories. Two repositories in very different stages of their life cycle exist in Germany, both are disused mines. For the ERAM repository (Endlager für radioaktive Abfälle Morsleben) decommissioning and closure is expected to start in 2029. Radioactive waste was last stored in 1998. For the KONRAD repository (Schachtanlage Konrad) commissioning and storage of radioactive waste is anticipated in 2030. The respective permits regulate, how the final repository is designed, what protective measures must be taken, which waste may be stored in what form and how the final repository is to be closed. ERAM and KONRAD were approved in 1986 and 2002, respectively; both approval processes took place in previous decades. Since then, both repositories have been continuously adapted to the current state of the art in science and technology. But what is the “current state of the art in science and technology”, who defines it and what does it mean for the approval of deep geological repositories? In this contribution we will show examples of how the state of the art in science and technology finds its way into supervision and licensing activities and which actors are involved. Finally, we discuss how we could optimize these processes and what we might learn for the permission of a repository for high radioactive waste.

How to cite: Schneider, S., Kause-Berg, H., and Baasch, F.: State of the art in science and technology for unique and lengthy administrative procedures - How does it work?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14424, https://doi.org/10.5194/egusphere-egu24-14424, 2024.

11:20–11:30
|
EGU24-14934
|
ERE3.3
|
Highlight
|
On-site presentation
|
Guido Bracke, Lena Maerten, and Christoph Borkel

The site selection for a repository for high-level radioactive waste (HLW) will take longer than the currently authorised period of 40 years for interim storage sites in Germany. Extension of this period could necessitate additional handling or measures, such as treatments of HLW. This might have an impact on radionuclide mobility in the final repository. Therefore, BASE initiated a research project that studied the behaviour of HLW in interim storage was studied for causes of degradation, effects and consequences and possible treatments, performed by GRS gGmbH. There are currently no indications for mandatory measures during the authorized period and beyond, but some hypothetical treatments were identified. These treatments were evaluated with regard to their impact on interim storage, radiation exposure for personal, manageability and radionuclide mobility in repositories. Measures include, for example, heating and earlier removal from interim storage for conditioning. Even though technical feasibility was not part of the study, it seems clear that with any of the identified measures, higher radiation doses would have to be expected for the personnel. The impact of these measures on radionuclide mobility in the repository is assessed to be low. However, a more quantitative assessment of the impact of hypothetical treatments appears only feasible when a repository concept including waste acceptance criteria is fixed, which is not the case at the time of the study.

How to cite: Bracke, G., Maerten, L., and Borkel, C.: Hypothetical measures on high-level radioactive waste from the perspective of extended interim storage and final disposal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14934, https://doi.org/10.5194/egusphere-egu24-14934, 2024.

11:30–11:40
|
EGU24-14693
|
ERE3.3
|
Highlight
|
On-site presentation
Marieke Rempe, Reinhard Fink, Florian Panitz, and René Romer

The site selection procedure for the deep geological storage of high-level radioactive waste in Germany started with a “white map”, i.e., with the entire federal territory, and considers all of three potential host rocks: rock salt, clay rock, and crystalline rock. In a first phase of the site selection procedure, Bundesgesellschaft für Endlagerung (BGE, i.e., Federal Company for Radioactive Waste Disposal) is determining regions for surface exploration based on the previously identified sub-areas that meet the minimum requirements defined by law. As the sub-areas cover approximately 54% of Germany's area, the site selection methodology must not only include safety assessments but must also lead to a significant safety-oriented reduction of the considered area towards the best-suited regions for surface exploration.

Several challenges arise for the determination of the regions for surface exploration. As legal regulations provide only a framework for the procedure but largely lack explicit assessment criteria, a methodology must be developed that is in accordance with the law and that also supplies the tools to evaluate and narrow down the remaining areas. In addition, the safety-oriented evaluation and area reduction must be done legally on the basis of available data only, which is sparsely available and mostly not specific to the needs for site evaluation. Only in the next phase of the site selection procedure can BGE collect data during surface exploration for a more detailed site characterization. Finally, the developed methodology, as well as decisions based on its application to the sub-areas, must be transparent and comprehensible to permit discussions with stakeholders and the public. Data availability and associated uncertainties provide a specific challenge in ensuring this transparency during the decision-making.

To address the challenges, BGE is developing a methodology that concretizes the legal requirements and translates them into a plausible evaluation system with well-defined criteria. These host-rock-specific evaluation criteria derived from the legal requirements allow a reproducible, systematic and thus transparent evaluation of safety-relevant attributes. The criteria are applied successively in a series of work steps, such that the level of detail and the strictness of requirements increase throughout the selection process. Thus, less-suitable areas are identified early on in the procedure with limited effort, while areas that are more promising are analyzed in greater detail – providing also the basis for a comparison between areas – and must pass successively higher requirements. The level of knowledge, which increases throughout the selection process, is taken into account when deciding on the evaluation criteria for a specific work step, such that heterogeneous data availability influences the decision-making as little as possible. However, poor data availability and verifiability of geologic realities are fundamental problems for the decision-making process that need to be addressed and discussed openly.

How to cite: Rempe, M., Fink, R., Panitz, F., and Romer, R.: Selection of regions for surface exploration in the search for a repository for high-level radioactive waste in Germany: Decision-making in a safety-oriented site selection procedure with sparsely available data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14693, https://doi.org/10.5194/egusphere-egu24-14693, 2024.

Numerical modelling of coupled processes
11:40–11:50
|
EGU24-3647
|
ERE3.3
|
Highlight
|
On-site presentation
Jens Birkholzer and Alex Bond

Here we provide an overview of an international research collaboration for advancing the understanding and modeling of coupled thermo-hydro-mechanical-chemical (THMC) processes in geological systems. The creation of the international DECOVALEX Initiative, now running for more than 30 years, was motivated by the recognition that prediction of these coupled effects is an essential part of demonstrating the performance and safety of radioactive waste disposal and other subsurface engineering applications. DECOVALEX emphasizes joint analysis and comparative modeling of state-of-the-art field and laboratory experiments, across a range of host rock options and repository designs. Participating research teams are from radioactive waste management and other organizations, national research institutes, regulatory agencies, universities, as well as industry and consulting groups, providing a wide range of perspectives and solutions to these complex problems. The most recent phase of the initiative, referred to as DECOVALEX-2023, started in 2020 and ended in December 2023. Modeling teams from 17 international partner organizations participated in the comparative evaluation of seven modeling tasks involving complex experimental and modeling challenges. The presentation provides examples of research contributions made within DECOVALEX-2023 and illustrates how these have helped building confidence in long-term performance predictions. These examples range from the modeling of large-scale in situ heater tests representing mock-ups of nuclear waste disposal tunnels, the analysis of gas transport tests in clay-based materials, the prediction thermal and gas pressure rock fracturing, to the comparison of performance assessment models.

The main characteristic of DECOVALEX is the close collaboration on analyzing and simulating state-of-the-art field and laboratory experiments, which provides a wide range of experiences, perspectives and solutions to these complex problems and allows for detailed comparison of analysis and modeling results. Much insight can be gained through this cooperative comparison of results from different research teams using different model approaches, not only on the effects of complex THMC processes, but also on the strengths, weaknesses, and adequacies of the various approaches and predictive models used by these research teams. We make the case in this presentation that DECOVALEX has contributed, and continues to contribute, to enhancing confidence in the technical adequacy of radioactive waste disposal, by improving our collective understanding of complex subsurface perturbations and coupled processes, by developing and comparing predictive models for these processes, by evaluating their uncertainties, by recognizing areas for additional research, and by emphasizing means of learning from each other and knowledge sharing. The insight and scientific knowledge gained would not have been possible if individual groups had studied these data alone rather than within a truly collaborative setting.

How to cite: Birkholzer, J. and Bond, A.: Overview of the DECOVALEX Initiative - Building Confidence Via Model Comparison, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3647, https://doi.org/10.5194/egusphere-egu24-3647, 2024.

11:50–12:00
|
EGU24-14633
|
ERE3.3
|
ECS
|
Virtual presentation
Christoph Lehmann, Thomas Nagel, and Olaf Kolditz

The identification of appropriate locations for secure nuclear waste disposal, a crucial aspect of Germany's nuclear phase-out strategy, remains a significant scientific, technical, and political challenge worldwide. The selection and safety assessment of sites demand extensive employment of numerical methods. The OpenWorkFlow project, initiated by Bundesgesellschaft für Endlagerung (BGE), is developing a new, open synthesis platform to virtualise repository systems. The simulation platform will evaluate far-field and near-field processes, aiding the site selection process first and geotechnical design of repository systems later on. Automated simulation and analysis pipelines developed in this project ensure the verifiability and reproducibility of all simulation results and the modularity of workflows brings flexibility, continuity and maintainability.

This project defines high scientific benchmarks and standards for numerical models and software development for the repository search in Germany. OpenWorkFlow as an efficient and holistic platform for numerical modelling will contribute to a science-based, transparent, and precise execution of the necessary safety assessments. This project includes all theoretical, numerical and computational methods and tools, including a virtual reality framework. OpenWorkFlow will be continuously developed by the core project team, but will also actively involve the community through its open concept (e.g. through the interactive benchmarking platform). This will create a win-win situation in the long run.

This talk is based on the paper Christoph Lehmann, Lars Bilke, Jörg Buchwald, Nico Graebling, Norbert Grunwald, Julian Heinze, Tobias Meisel, Renchao Lu, Dmitri Naumov, Karsten Rink, Ozan Özgür Sen, Philipp Selzer, Haibing Shao, Wenqing Wang, Florian Zill, Thomas Nagel, and Olaf Kolditz. Openworkflow - development of an open-source synthesis-platform for safety investigations in the site selection process. Grundwasser, 2024. in print.

How to cite: Lehmann, C., Nagel, T., and Kolditz, O.: OpenWorkFlow - Development of an open-source synthesis-platform for safety investigations in the site selection process, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14633, https://doi.org/10.5194/egusphere-egu24-14633, 2024.

12:00–12:10
|
EGU24-9854
|
ERE3.3
|
On-site presentation
Carlos Guevara Morel, Jan Thiedau, and Jobst Maßmann

Safe deep geological disposal of heat-generating nuclear waste requires an accurate assessment of barrier integrity. Therefore, the evaluation of the coupled mechanical, hydraulic, thermal and chemical processes, occurring in the host rock due to the nuclear waste storage, excavation among others is needed. For this purpose, numerical modeling is an essential and powerful tool. This contribution focuses on a generic repository system that relies on a Containment Providing Rock Zone (CRZ) in a crystalline rock, which acts as the principal containment barrier according to German law. Using the open-source finite element code OpenGeoSys version 6, a closer look at the CRZ regarding the influence of fractures on the local hydraulics and potentially available rock zone volume for repository emplacement is shown.

Since fractures and other type of discontinuities usually characterize crystalline rock, they are expected to influence the hydraulic behavior of the system. Hence, their representation in numerical models becomes non-trivial. Here a comparison between different numerical fracture representations and their impact on the hydraulic regime surrounding the CRZ, is presented.

Due to the presence of fractures, it cannot be assumed that a sufficiently large area in which to emplace the waste will be found. As a consequence, multiple smaller CRZs [1], each providing undisturbed rock, have to be defined. Typically, it is only possible to characterize fracture networks statistically, which leads to the use of stochastically generated discrete fracture networks. Using a geometrical characterization of the potentially undisturbed CRZs based on a stochastically generated discrete fracture network, a methodology is proposed to evaluate the feasibility of the multiple CRZs concept.

References

[1] Thiedau, J., et al.: CHRISTA-II - Analysen zur Integrität von geologischen Barrieren von Endlagersystemen im Kristallin. Ergebnisbericht, Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover, 2021

How to cite: Guevara Morel, C., Thiedau, J., and Maßmann, J.: Advances in the numerical modeling strategy (concept) of a generic nuclear waste repository in crystalline rock, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9854, https://doi.org/10.5194/egusphere-egu24-9854, 2024.

12:10–12:20
|
EGU24-6012
|
ERE3.3
|
ECS
|
On-site presentation
Feliks Kiszkurno, Jörg Buchwald, Olaf Kolditz, and Thomas Nagel

Pore pressure evolution and hydraulic flow are two important physical features to consider in barrier integrity and radionuclide transport applications. Existing literature suggests a potentially non-negligible impact of thermo-osmosis on pore-pressure evolution due to thermal gradients in clay rocks without arriving at a consensus. Numerical experiments based on models are a widely used method in the geosciences to test the relevance of physical features under specified conditions. Mismatch between the observations and the simulation can be partially attributed to the assumptions and simplifications made when developing those models. Their impact on the results and conclusions drawn from the numerical experiments can be significant and thus needs to be explored. Such exploration can proceed by jointly investigating the uncertainty associated with modelling choices, process selection and calibration. This study applies a hypothesis-testing method based on an assisted-history-matching workflow to integrate uncertainty evaluation of model selection, process representation and parameter identification. Three models were compared, representing, respectively, the correct, approximate and wrong hypotheses with respect to a synthetic data set resembling the ATLAS experiment, an in-situ, full-scale heating experiment performed at the HADES underground laboratory in Mol, Belgium. We show that the approach can recover the correct modelling hypothesis in the presence of parameter uncertainty despite competing hypothesis with the same amount of parametric degrees of freedom.

How to cite: Kiszkurno, F., Buchwald, J., Kolditz, O., and Nagel, T.: Hypothesis-testing and assisted-history-matching applied to evaluate uncertainty of model selection and parameter values: a case study of the impact of thermo-osmosis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6012, https://doi.org/10.5194/egusphere-egu24-6012, 2024.

12:20–12:30
|
EGU24-15328
|
ERE3.3
|
On-site presentation
Norbert Grunwald, Thomas Nagel, Michael Pitz, and Olaf Kolditz

This study explores the numerical simulation of gas transport in low-permeable rocks, specifically focusing on clay rock. Utilizing the finite-element method, we examine the transition from single-phase to two-phase flow conditions. Our approach diverges from traditional methods by avoiding persistent primary variables or variable switching. We validate our methodology through two benchmark tests: the first simulates gas injection relevant to radioactive waste disposal, while the second models a core drilling experiment that induces mechanical unloading.

Our findings are significant for understanding gas behavior in geological formations, particularly in the context of nuclear waste disposal and CO2 storage. We offer a novel perspective on managing phase transitions in non-isothermal environments, bolstered by an extensive analysis of secondary variables. The outcomes of this research contribute to the improved modeling of large-scale repository systems, highlighting the intricacies and complexities involved in gas transport within clay rock.

This paper not only provides insights into the physical processes underpinning gas movement in these environments but also proposes a scalable and adaptable framework for future research in similar geological contexts.

How to cite: Grunwald, N., Nagel, T., Pitz, M., and Kolditz, O.: Finite-Element Analysis of Phase Transitions in Gas Migration within Clay Rock, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15328, https://doi.org/10.5194/egusphere-egu24-15328, 2024.

Lunch break
14:00–14:05
14:05–14:15
|
EGU24-2049
|
ERE3.3
|
Highlight
|
On-site presentation
Holger Steffen and Rebekka Steffen

Continental-scale glaciations lead to deformation, geopotential, rotation, and stress changes of the Earth. Especially glacially induced stress changes in the lithosphere can significantly impact potential nuclear waste repository sites, planned for depths a few hundred meters below ground. Ensuring the long-term stability of these sites warrants analyzing such additional stresses in the crust that might be imposed by future ice sheets during forthcoming glaciations. We focus on North America by investigating the past to quantify such stresses.

Utilizing a refined, high-resolution North American ice history spanning 122,000 years from the University of Toronto Glacial Systems Model, alongside various one- and three-dimensional earth structures, we investigate the dynamic nature of glacially induced stresses at Canada’s candidate sites South Bruce and Ignace. Both sites are situated in Ontario but 1000 km apart. Additionally, we examine the corresponding deformation and strain changes.

We find that both sites undergo strong variations in glacially induced stresses and strains over a glacial cycle. Especially the horizontal components can change from tensional to compressive within a few thousand years due to fluctuations in ice cover. Surprisingly, despite South Bruce's location farther from the ice sheet center and its temporary position in the forebulge of the ice sheet, stress and strain magnitudes resemble those of Ignace. Moreover, there's potential at South Bruce for altering the direction of pre-existing maximum horizontal stress. Interestingly, the choice of earth structure in the modelling affects strain more than stress.

Although the sites are 1000 km apart, our results do not indicate a superior repository site. Instead, they emphasize the need to integrate our findings into the site selection process and barrier integrity assessment. We recommend further studies focusing on a stress analysis with more detailed earth models, considering faults and lineaments near the candidate sites.

This research was funded by the Nuclear Waste Management Organization, Canada.

How to cite: Steffen, H. and Steffen, R.: Impact of glacially induced stresses and strains at Canadian candidate sites for nuclear waste disposal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2049, https://doi.org/10.5194/egusphere-egu24-2049, 2024.

14:15–14:25
|
EGU24-15947
|
ERE3.3
|
ECS
|
On-site presentation
On the role of plastic flow in THM simulations capturing glacial cycle effects on German nuclear waste repositories in clay rock
(withdrawn)
Christian Silbermann, Florian Zill, Tobias Meisel, Dominik Kern, Thomas Nagel, and Olaf Kolditz
14:25–14:35
|
EGU24-16099
|
ERE3.3
|
Highlight
|
On-site presentation
Matthias Brandt, Anton Carl-Dworschak, Andreas Jockel, and Rene Kahnt

The site selection procedure in Germany is searching for a site with the best possible safety for a repository for high-level waste (HLW). The integrity of the overburden is crucial in the assessment of the best possible safety (StandAG §23 (5), para.3). Beyond the safe inclusion in the selected host rock for a HLW repository, a sufficient stability of the overlaying overburden horizons must be ensured. Erosion by glaciation induced processes are but one of the potential threats to the stability of these overburden horizons. The research project presented here is funded by BASE under the grant number FKZ 4721F10401.
Within the research project “Evaluation of methods and models to predict the protective function of the overburden in Germany over the period of 1 Ma” (MeMoDeck) a framework to assess the risks introduced by glacial erosion that are to be expected within 1 million years was developed. As an indication of this, the erosion processes, prevailing during the Pleistocene, have been analysed with respect to the extent of the erosion depth introduced by them. The largest depths are attained to incisions by subglacial meltwater transport in the form of tunnel valleys. 
The authors employed a combined modelling approach, which includes a three-dimensional deterministic numerical modelling of the tunnel valley genesis with FLAC3D and a multivariate probabilistic modelling with GoldSim to account for the remarkable uncertainties over 1 Ma. The uncertainties result from the lack of data with respect to hydraulic conditions during the melting of the ice sheet and the variability of the erosion resistance of the geological horizons of the overburden, which overlies the respective host rock. 
The authors determine the depth of a prospective tunnel valley by a simulation at well-constrained geological and melt water conditions by the deterministic FLAC3D model.
The results from the deterministic modelling with Flac3D are the basis of the simulation within the probabilistic model with GoldSim, which relaxes the modelling constraints towards melt water and geological properties using statistical distribution functions for these quantities.
The results of the modelling will be presented and the most influential parameters towards the final depths of the overburden incisions will be discussed.

How to cite: Brandt, M., Carl-Dworschak, A., Jockel, A., and Kahnt, R.: Modelling of glacial melt water erosion of the overburden of a HLW over 1 million years, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16099, https://doi.org/10.5194/egusphere-egu24-16099, 2024.

EDZ and backfill characterization
14:35–14:45
|
EGU24-4976
|
ERE3.3
|
ECS
|
On-site presentation
Lisa Maria Ringel, Rémi de la Vaissière, Ralf Brauchler, and Peter Bayer

In the safety assessment of a nuclear waste repository, it is crucial to identify and isolate possible pathways for radionuclides from the waste canister to the biosphere and vice versa. Despite the potential self-sealing properties depending on the host rock and the decrease of the permeability over time, the migration depends on the presence of a fracture network, the connectivity of the fractures, and their connectivity to tunnels or drifts. To describe the initial state of said pathways, we demonstrate the inversion of transient pressure measurements to delineate the structural and pneumatic properties of an excavation-induced fracture network at the Meuse/Haute-Marne Underground Research Laboratory (URL) operated by the French radioactive waste management agency ANDRA.

The tomographic tests were carried out as sequential constant-rate injections of nitrogen and the resulting pressure perturbations were recorded in nearby borehole intervals. In total, nine boreholes with two injection/monitoring intervals each are available on a volume of approximately 3m times 3m times 5m. Therefore, the joint inversion of more than 300 signals allows unique insights into the excavation-induced fracture network.

A discrete fracture network (DFN) model is applied for the forward and inverse modeling. Thereby, the strong heterogeneity of the distribution of hydraulic or pneumatic properties caused by the fracture network can be described. A numerical model is used to simulate the transient pressure diffusion in the DFN. The structural properties and the permeability of the DFN model are characterized by solving the inverse problem. The inversion relies on a stochastic model of the DFN parameters based on the Bayesian equation. The posterior distribution, i.e., the distribution of the DFN parameters given the measured data, is the product of likelihood and prior distribution. The likelihood function compares the error between the measured data and the simulated outcome of the tomography experiments for a given DFN model. The prior distribution includes information about the fracture properties obtained in previous studies. The posterior distribution is characterized by generating samples from the posterior with Markov chain Monte Carlo (MCMC) methods. Due to the unknown number of fractures, the insertion and deletion of fractures are possible according to the reversible jump MCMC algorithm.

The inversion approach results in several DFN realizations that are approximately equally likely which is illustrated in a fracture probability map and a map of the permeability distribution. Thereby, preferential flow paths can be characterized.

How to cite: Ringel, L. M., de la Vaissière, R., Brauchler, R., and Bayer, P.: Three-dimensional characterization of an excavation-induced fracture network with gas tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4976, https://doi.org/10.5194/egusphere-egu24-4976, 2024.

14:45–14:55
|
EGU24-16507
|
ERE3.3
|
On-site presentation
Mikel Dieguez, Jesús Morejon, Manuel Mingarro, Miguel García-Gutiérrez, Tiziana Missana, Patrik Sellin, and Úrsula Alonso

Compacted bentonite is the primary engineered barrier in a deep geological repository for high-level radioactive waste. The bentonite must exhibit a sufficiently high swelling capacity and low hydraulic conductivity to seal the waste and to hinder radionuclide migration (Sellin & Leupin, 2013). The erosion of the barrier due to the flow of groundwater, which promotes clay swelling and expansion through fractures in the crystalline host rock, would entail a loss of mass in the bentonite, which could compromise the effectiveness of the barrier.

Bentonite erosion is usually experimentally studied at laboratory scale, by analyzing the role of different parameters such as the type of clay, water chemistry or the physical conditions of the fracture in a controlled manner. The extrapolation of laboratory results to a real repository requires compulsory evaluating the role of those aspects more sensitive to scale effects. This study investigated whether the amount of clay emplaced or the clay surface in contact with fractures play a role in erosion process.

For this, an experimental set-up to simulate an artificial fracture was used (Alonso et al., 2019). In this setup, a compacted bentonite sample is placed between two methacrylate plates with a known aperture. All experiments were performed at a dry density of 1.4 g/cm3 with a previously sodium equilibrated clay (NANOCOR®). Fractures are placed in horizontal position and filled with a low saline solution (10-3 M NaCl), to monitor the expansion distances of the clay in the fracture by periodic photographs. The clay is allowed to expand during 30 days and the amount of clay eroded is quantified post-mortem. Two sets of experiments were carried out, the first set evaluated the impact of clay area exposed to hydration in the fracture, fixing the amount of clay mass, with samples of ring geometry. For the second set, the clay exposed surface contacting the fracture was kept constant, but the amount of clay installed was varied with cylindrical compacted samples of variable height.

Results showed that clay expansion can only occur in water conductive fractures, and no expansion was observed in the inner zone of the ring geometry tests, which were not water filled. Additionally, no large differences in the expansion distance were observed in the tests with a larger exposed surface area. For the second set of experiments with cylindrical geometry and the same exposed area, it was observed that the expansion and mass loss did not vary significantly with different clay mass. The indication is that in a genuine repository featuring substantially greater volumes of clay, the impact of this factor on its expansion should not be considerable.

REFERENCES

Alonso, U., Missana, T., García-Gutiérrez, M., 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., Sellin, P., and Alonso, Ú.: Bentonite erosion by expansion in fractures: effect of exposed surface and clay mass, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16507, https://doi.org/10.5194/egusphere-egu24-16507, 2024.

14:55–15:05
|
EGU24-7469
|
ERE3.3
|
ECS
|
On-site presentation
Tuanny Cajuhi, Gesa Ziefle, Jobst Maßmann, Thomas Nagel, and Keita Yoshioka

Assessing barrier integrity under varying environmental conditions is crucial in the context of radioactive waste disposal. This study, originally  conducted at the Mont Terri Rock Laboratory in Switzerland within the Cyclic Deformation (CD-A) experiment, gains new understanding in this context. The laboratory, located within an Opalinus Clay formation, has been also instrumented to observe the triggers of desiccation cracking in open and closed excavations. Seasonal changes play an important role especially during winter where the relative air humidity reduces and drives desiccation cracking. To model this dynamic, we employed a hydro-mechanical model incorporating macroscopic poromechanics, the Richards equation for partial saturation and the phase-field modeling approach for cracking. Key to our study was the evaluation of unsaturated hydro-mechanical responses using field-acquired parameters such as the measured crack apertures, supplemented by existing literature. We established a good correlation between the observed and calculated crack formation by using the measured seasonal changes in relative air humidity as boundary condition as well as using  homogeneously and randomly distributed material parameters [1]. Furthermore, our study delves into the implications of enhanced permeability due to cracking on barrier integrity. Our findings offer insights into the dynamics of crack development and their implications, thereby making an  incremental contribution to the broader goal of ensuring safe and effective management of radioactive waste disposal.

[1] T. Cajuhi, G. Ziefle, J. Maßmann, T. Nagel and K. Yoshioka, Modeling desiccation cracks in Opalinus Clay at field scale with the phase-field approach. InterPore Journal (in press).

How to cite: Cajuhi, T., Ziefle, G., Maßmann, J., Nagel, T., and Yoshioka, K.: Modeling in-situ desiccation cracks in a ventilated niche using homogeneously and randomly distributed material parameters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7469, https://doi.org/10.5194/egusphere-egu24-7469, 2024.

15:05–15:15
|
EGU24-3238
|
ERE3.3
|
On-site presentation
Florie Caporuscio, Marlena Rock, and Amber Zandanel

The United States initiated the Spent Fuel and Waste Storage and Transport (SFWST) Campaign over ten years to evaluate various generic geological repositories for the disposal of spent nuclear fuel. Most previous international work describes Engineered Barrier Systems (EBS) for repositories focused on low temperature conditions. Our hydrothermal experiments on EBS materials were conducted to characterize high temperature interactions of bentonite clay and argillite wall rock +/- cement with candidate waste container steels (304SS, 316SS, low-C steel).

Over eight years of hydrothermal experiments were performed using Dickson reaction cells at temperatures ranging from 150 to 300°C and pressures of 15 – 16 MPa, respectively, for five to eight weeks. Wyoming bentonite was saturated with a 1,900 ppm K-Ca-Na-Cl solution in combination with stainless and low-C steel coupons to replicate EBS conditions in deep geological disposition of nuclear spent fuel. The solid-reaction products and steel coupons were characterized post experiment via XRD, XRF, SEM, and EMP.

Preliminary mineralogic phase transformations for the experiments are as follows: Smectite clays did not transition to illite,. Clinoptilolite, appears to have formed from the remnant glass which was present in the original bentonite. The Si/Al ratios for the clinoptilolite are dominantly between 4 and 6. The Na/(Na+Ca) values range from 0.55 to 0.75. Calcite and gypsum were also observed as minor reaction products. Aqueous SiO2 remains saturated with respect to quartz throughout the experiments.

Our experiments focused on bentonite-cement interactions, including 1) Baseline bentonite stability in argillite, 2) reactions with Uncured OPC powder, 3) Cured OPC chip, and 4) Low-pH cement chips. In the Opalinus Clay, Wyoming bentonite + OPC powder experiments (#2), spherical, calcium aluminum silicate hydrate (CASH) phases formed within the fine-grained clay matrix. Based on the composition of this mineral, the C(A)SH phases are likely a hydrated calcium silicate, such as Al-tobermorite (Ca4.3Si5.5Al 0.5O16(OH)2•4(H2O)). Very Ca-rich hydrous minerals, such as Al-tobermorite, have been observed in experiments involving bentonite and cement with highly alkaline bulk chemistries and pH > ~10 (Savage et al., 2007).

 

The formation of CASH minerals contrasts with the products of previous experiments with Wyoming Bentonite ± Opalinus Clay host rock (#1), in which zeolites (analcime–wairakite solid solution) formed that have similar morphologies and textural contexts.

 

The experiments with cured OPC chips (#3) resulted in Portlandite dissolution during the early elevated pH values, but pH values stabilize at near-neutral values by equilibrium. Montmorillonite was stable, and zeolite formation was observed throughout the groundmass of the reaction products but was not abundant at the bentonite-cement interface. Reactions between the groundwater solution, bentonite, and the low-pH cement (#4) resulted in a lower steady-state silica concentration than reactions between groundwater solution, bentonite, low-pH cement, and Opalinus Clay wall rock. This suggests a controlling input on silica concentrations is affected by Opalinus Clay wall rock that is not advanced by the bentonite or low-pH cement alone.

 

How to cite: Caporuscio, F., Rock, M., and Zandanel, A.:  Argillite Host Rock and Cement - Engineered Barrier System Experiments: Mineralogical Evolution at Repository Pressures and Temperatures., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3238, https://doi.org/10.5194/egusphere-egu24-3238, 2024.

15:15–15:25
|
EGU24-3566
|
ERE3.3
|
ECS
|
On-site presentation
Louis Schaarschmidt and Helmut Mischo

With nuclear energy being one of the trending topics in the world regarding energy supply, at the same time the question for safe disposal of the high-level radioactive waste becomes increasingly popular in the public. 

The TU Bergakademie Freiberg wants to provide answers to this challenging task by practical big-scale in-situ underground tests and new backfill material development. The underground mining chair commenced the GESAV (Gefügestabilisierter Salzgrusversatz; engl.: Matrix-stabilized salt grit backfill) project series back in 2013 with the development of a matrix-stabilized salt backfill which solidifies in an early stage by the development of internal polyhalite crystals. The innovative material combines the benefits of a salt backfill material with a stability compared to conventional materials, such as cement like building materials.

The GESAV project series has been finished in 2021 with the successful proof of the big-scale practical applicability of the matrix-stabilized backfill by building several backfill bodies underground with different methods from the conventional underground mining industry.

The goal for the currently going-on SAVER (Entwicklung eines salzgrusbasierten Versatzkonzeptes unter der Option Rückholbarkeit; engl.: Development of a salt grit based backfilling concept with regards to retrievability) project is to build and compare a GESAV material backfill body to a conventional salt backfill body, since in the GESAV II project only the in-situ applicability of the GESAV material in general has been researched. Both of the test drifts in the Sondershausen rock salt underground mine have the same dimensions and are instrumented exactly the same. Moreover, a radioactive waste casket dummy has been developed within the project and placed into the backfill bodies in order to simulate a real-life backfilling process. So far, both backfill bodies have been built with a slinger-vibration-backfill method that already highlighted very high in-situ densities in the GESAV II project (2017-2021). Not only did this validate the applicability of the method on GESAV material but also proved that it is transferable to other salt backfill materials.

During the building process of both bodies, a big sampling campaign was carried out in order to gain an insight into actual possible built-in in-situ densities and other parameters that are relevant for further optimization and understanding of real-life backfilling in a mining scale. Once analyzed, the samples, in combination with the other sensors, can provide a deep insight and further understanding of the geochemical and mechanical properties of both backfill bodies. The sensor data shows that GESAV material highlights better properties regarding settlement than conventional salt grit as well as pressure distribution within the backfill body. The measurement systems will continue to run as long as the project is taking place in order to continuously gain an insight into ongoing processes within both backfill bodies. With the chosen sensor setup as well as the sampling regime it is expected to gain more valuable insights into actual underground in-situ behavior of those materials in the near future. Those insights are very likely to contribute to the ongoing question of developing a feasible concept for high-radioactive waste disposal in rock salt formations.

How to cite: Schaarschmidt, L. and Mischo, H.: Big Scale In-Situ Application of Matrix-stabilized vs. Conventional Salt Grit Backfill with Use of Improved Backfilling Method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3566, https://doi.org/10.5194/egusphere-egu24-3566, 2024.

15:25–15:35
|
EGU24-8817
|
ERE3.3
|
ECS
|
On-site presentation
Anita S. Katheras, Konstantinos Karalis, Matthias Krack, Andreas C. Scheinost, and Sergey V. Churakov

In many European countries (e.g., France, Switzerland), thick steel casks are foreseen for the containment of high-level radioactive waste in deep geological repositories. In contact with pore-water, steel corrodes forming mixed iron oxides, mainly magnetite (Fe3O4). After tens of thousands of years, the casks may breach allowing for leaching of the radionuclides (e.g., Tc and Pu) into pore-water. The radionuclides can be retarded by corrosion products either by adsorption or via structural incorporation [1,2]. The molecular scale mechanisms of these phenomena are investigated by ab initio simulations and X-ray absorption spectroscopy (XAS).

The dominant low-index surfaces of magnetite particles and their termination at the relevant conditions were identified based on Kohn-Sham density functional theory (DFT), using the open-source CP2K code [3]. The DFT+U method was employed for the strongly correlated 3d and 5f electrons of Fe and Pu, respectively. After benchmarking the model setup, the surface energies of the (111) facet with different surface terminations and water coverage were analyzed as a function of redox conditions and pH. The Eh and pH predominance diagram could be predicted for the most stable surfaces under real repository conditions [4]. Further, we confirmed these findings for nanocrystals with approximately 2 nm size. Subsequently, ab initio molecular dynamics (MD) were applied to simulate sorption structures of radionuclides on the expected magnetite (111) surfaces based on experimental findings [2,5].

[1] R. Kirsch et al. Oxidation State and Local Structure of Plutonium Reacted with Magnetite, Mackinawite, and Chukanovite. Environmental Science & Technology, 2011, 45(17), 7267.

[2] E. Yalçintaş et al. Systematic XAS study on the reduction and uptake of Tc by magnetite and mackinawite. Dalton Transactions, 2016, 45(44), 17874.

[3] T. D. Kühne et al. CP2K: An Electronic Structure and Molecular Dynamics Software Package - Quickstep: Efficient and Accurate Electronic Structure Calculations. The Journal of Chemical Physics, 2020, 152(19), 194103.

[4] A.S. Katheras et al. Stability and Speciation of Hydrated Magnetite {111} Surfaces from Ab Initio Simulations with Relevance for Geochemical Redox Processes. Environmental Science & Technology, 2024, 58(1), 935.

[5] T. Dumas et al. Plutonium Retention Mechanisms by Magnetite under Anoxic Conditions: Entrapment versus Sorption. ACS Earth & Space Chemistry, 2019, 3(10), 2197.

How to cite: Katheras, A. S., Karalis, K., Krack, M., Scheinost, A. C., and Churakov, S. V.: Ab initio modelling of magnetite surfaces for radionuclide retention, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8817, https://doi.org/10.5194/egusphere-egu24-8817, 2024.

15:35–15:45
|
EGU24-20815
|
ERE3.3
|
On-site presentation
Veronika Hlavackova, Trung Duc Le, Jakub Riha, Petr Vecernik, Tomas Cernousek, Lucie Hausmannova, Radek Vasicek, and Alena Sevcu

Low-pH concrete (LPC) is used as one of the main construction components of deep geological repositories (DGR) for radioactive waste. The mechanical and chemical stability of this material is crucial for the long term DGR sustainability. However, the presence of microorganisms in the underground environment and backfill matrices could significantly affect its stability and in turn the safety of DGRs. The buffer and backfill matrix (bentonite) and underground water are potential long-term sources of bacteria in DGR. The WP MAGIC as a part of the European joint program EURAD focuses on studying the chemo-mechanical behavior of concrete under varied conditions. The project compares the effect of three different conditions – air, water and bentonite - on aged SURAO LPC samples. The 2-year experiment is disposed in Czech Underground Research Facility (URF) Bukov. Our aim was to investigate microbial activity in LPC discs and describe the capability of present microorganisms to affect the mechanical properties of LPC in time. The microbiological analysis comprised of both cultivation dependent and independent approach. The microbial activity was also confirmed using epifluorescent microscopy and scanning electron microscopy. Our findings reveal unique microorganisms in each of in-situ condition, highlighting their potential effect on mechanical properties of LPC.

How to cite: Hlavackova, V., Le, T. D., Riha, J., Vecernik, P., Cernousek, T., Hausmannova, L., Vasicek, R., and Sevcu, A.: Microbiological Analysis of SURAO Low-pH Concrete (LPC) in repository-like conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20815, https://doi.org/10.5194/egusphere-egu24-20815, 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
X4.165
|
EGU24-1685
|
ERE3.3
Monika Sobiesiak, Katrin Plenkers, Thomas Fischer, Edgar Manukyan, and Thomas Spillmann

One important aspect of implementation of deep underground radioactive waste repositories is the physical characterization of backfill material which fills the voids between waste containers and ambient host rock. The Mont Terri Rock Laboratory, located in NW Switzerland and operated by swisstopo, is an international subterranean research facility which offers a perfect environment to carry out experimental test phases on such barrier systems. In this study, we report on eight years of ultrasonic monitoring in the bentonite backfill of the FE-Experiment, which aims at monitoring long-term changes in material properties of the backfill around a simulated radioactive waste repository under the conditions of rising temperature and increasing humidity. The FE Experiment is a full-scale heater test in the Opalinus clay. It simulates the construction, waste emplacement, backfilling and early post-closure evolution of spent fuel (SF)/vitrified high level waste (HLW) repository tunnel (Mueller et al., 2017).

 

The monitoring method is based on the generation of seismic signals in the frequency range of 1000 Hz to 100 kHz emitted and received by acoustic sensors. In total, 17 sensors (4 emitters and 13 receivers) manufactured by GmuG, form two different arrays. One is a permanent array installed within the bentonite material itself, responsible for measuring the ultrasonic transmission on a cross section through the tunnel in front of the heater closest to the concrete plug that closes the tunnel. The second array is installed within plexiglass pipes that were mounted in the roof area of FE tunnel and reach beyond the same cylindrical heater. Each night, from 22:00 to 06:00 the next morning, repeated delta signals are generated by the emitters and the respective wavefields are recorded by the receiving sensors.

 

The P and S phase first arrivals of the stacked waveforms are used then to estimate seismic velocities. The ongoing experiment is a unique longterm observation of the process within the bentonite. We show that, besides a general increase in velocities over time, the measurements resolve distinct differences in various areas within the backfill. For a ray path on the cross section, the P-wave velocity increased by approximately 100 m/s, from 550 m/s in 2015 to 642 m/s in 2023. Dividing the monitored area into the different sections, we find that seismic velocities in the floor area of the tunnel show higher values than in the roof area. Considering the entire wavefields at each sensor over time, we observe strong changes in waveform characteristics by disappearing of entire phases or changes in amplitudes. All observations reflect changes in material properties over time. The reasons for different seismic velocities in roof and floor area of the tunnel might lie in the graveled texture and swelling of particles due to increasing humidity and/or in a compaction process which is faster at the bottom of the tunnel. The process of velocity increase in the bentonite backfill is still ongoing at most of the emitter – receiver combinations.

 

How to cite: Sobiesiak, M., Plenkers, K., Fischer, T., Manukyan, E., and Spillmann, T.: Determination of Seismic Velocities in Bentonite Backfill Through Ultrasonic Measurements in the FE-Experiment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1685, https://doi.org/10.5194/egusphere-egu24-1685, 2024.

X4.166
|
EGU24-6036
|
ERE3.3
Haibing Shao, Philipp Selzer, Christoph Behrens, Christoph Lehmann, Phillip Kreye, Wolfram Rühaak, and Olaf Kolditz

Finding the best-suited location for safely storing high-level nuclear waste is more than a scientific challenge for a country. In Germany, the legal requirements demand a safe containment of high-level nuclear waste for at least one million years within a deep geological repository. In this context, the site selection procedure demands a validated model to predict the reactive transport of radionuclides in layered subsurface formations with varying physical and chemical properties. In this work, we compare the modelling capabilities of TransPyREnd, which is a one-dimensional transport code based on finite differences, especially developed for the quick estimation of radionuclide transport, with an established geoscientific simulator OpenGeoSys, which is capable of coupled thermo-hydro-mechanical-chemical modelling based on finite elements in three spatial dimensions. Both codes are going to be used in the site selection procedure for the German nuclear waste repository. The example host rock formation for benchmarking is the Opalinus clay located in southern Germany, which is modelled using a simplified and preliminary parametrization. We enhance the validation analysis by also benchmarking against an analytical solution for a homogeneous material. The modelling results suggest that both TransPyREnd and OpenGeoSys are capable of consistently modelling the distribution of radionuclides within the geological barrier over long timescale. The discussion further goes to the applicability of different approaches for serving as tools in the site selection procedure, with minor differences in their predictive capabilities, limitations, and possible pitfalls to be avoided for the accurate prediction of radionuclide transport over geological times.

How to cite: Shao, H., Selzer, P., Behrens, C., Lehmann, C., Kreye, P., Rühaak, W., and Kolditz, O.: Validation and benchmarking of simplified reactive transport models of radionuclides for the assessment of nuclear waste repositories, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6036, https://doi.org/10.5194/egusphere-egu24-6036, 2024.

X4.167
|
EGU24-6051
|
ERE3.3
Dominik Kern, Fabien Magri, Holger Steffen, and Thomas Nagel

Deep geological repositories (DGRs) are designed to isolate radioactive waste (RW) from the biosphere over extremely long-time scales (i.e., several hundred thousand years). In order to assess the robustness of a safety case for a DGR, it is therefore necessary to analyse probable, less probable and hypothetical future developments due to, for example, climate change. Climate models predict that several ice sheets will advance and retreat over the next several thousands years. Glacial isostatic adjustment (GIA), resulting from the large moving mass of an ice sheet, can alter the displacement and far-field stress field of a DGR.

Due to their extremely low matrix permeability, crystalline rocks are suitable host rocks for the disposal of RW in DGRs. However, the mechanical properties of crystalline rocks often promote crack growth and faulting, which in turn compromise their barrier function with respect to groundwater flow. In the INFRA project (DFG NA1528/2-1 and MA4450/5-1), we quantify how faults prone to reactivation during glacial events can affect radionuclide migration around a DGR in crystalline rock.

We apply boundary conditions derived from an established GIA model [1,2] to a finite element model [3,4] of coupled fluid flow and radionuclide transport to numerically solve the component transport problem before and after fault reactivation. The Coulomb failure stress criterion is used as an indicator of permeability changes. The simulations show that GIA can increase permeability in the upper 400m of the reactivated faults. There, groundwater flow enhances radionuclide migration along the fault. In contrast, groundwater flow is reduced in the direction perpendicular to the fault plane. Although the proposed numerical workflow has been applied to the case of GIA, it can also be adapted to study hydromechanical processes induced by seismic events or by hydrofracking in enhanced geothermal systems.

 

[1] Argus, D.F., Peltier, W.R., Drummond, R., Moore, A.W.: The Antarctica component of postglacial rebound model ICE-6G C (VM5a) based on GPS positioning, exposure age dating of ice thicknesses, and relative sea level histories. Geophysical Journal International 198(1), 537–563 (2014)
https://doi.org/10.1093/gji/ggu140

[2] Peltier, W.R., Argus, D.F., Drummond, R.: Space geodesy constrains ice age terminal deglaciation: The global model. Journal of Geophysical Research: Solid Earth 120(1), 450–487 (2015)
https://doi.org/10.1002/2014JB011176

[3] Bilke, L., Flemisch, B., Kalbacher, T., Kolditz, O., Helmig, R., Nagel, T.: Development of Open-Source Porous Media Simulators: Principles and Experiences. Transport in Porous Media 130(1), 337–361 (2019)
https://doi.org/10.1007/s11242-019-01310-1

[4] Bilke, L., Fischer, T., Naumov, D., Lehmann, C., Wang, W., Lu, R., Meng, B., Rink, K., Grunwald, N., Buchwald, J., Silbermann, C., Habel, R., Günther, L., Mollaali, M., Meisel, T., Randow, J., Einspänner, S., Shao, H., Kurgyis, K., Kolditz, O., Garibay, J.: OpenGeoSys. Zenodo (2022)
https://doi.org/10.5281/zenodo.7092676

How to cite: Kern, D., Magri, F., Steffen, H., and Nagel, T.: Effects of glacial isostatic adjustment on fault reactivation and its consequences on radionuclide migration in crystalline host rock, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6051, https://doi.org/10.5194/egusphere-egu24-6051, 2024.

X4.168
|
EGU24-6908
|
ERE3.3
Yong-Ki Lee, Chae-Soon Choi, and Kyung-Woo Park

Rock masses characterized by low permeability (e.g. crystalline rocks) have been considered as natural barriers in the deep geological disposal of high-level radioactive waste. Therefore, groundwater flows within the natural barriers are typically governed by the spatial distribution of fractures within the rock mass. This study focuses on introducing an experimental system designed to evaluate hydro-mechanical properties in the natural barriers. This system allows hydro-mechanical experiments on fracture specimens by employing fluid injection under true triaxial compression conditions. The principal stress state of the underground rock mass can be induced through true triaxial compression conditions, providing the means for its application in the analysis of site-specific properties associated with rock fractures. In particular, the main feature of the experimental system is its capability for bidirectional fluid injection, allowing for hydro-mechanical experiments to be conducted on both individual and intersecting fractures. Detailed specifications have been designed considering the principal stress and groundwater conditions surrounding the KURT (KAERI Underground Research Tunnel), an underground research laboratory in Korea. The preliminary experiments utilizing the constructed experimental system confirmed that true triaxial compression conditions could be implemented while sustaining the loading speed and target stress at a reasonable level. Moreover, it was demonstrated that stable bidirectional fluid injection conditions could be achieved. The examination of applicability was also carried out by employing the experimental system to derive fracture apertures, which represent the hydro-mechanical properties of rock mass. In future investigations, we plan to conduct various hydro-mechanical experiments, employing fracture specimens sampled from the KURT site. This effort is expected to contribute to developing a Korean hydro-mechanical coupled model by evaluating the fracture properties in the KURT site.

Keywords: experimental system, bidirectional fluid injection, true triaxial compression, hydro-mechanical properties, natural barriers

Acknowledgements: This work was supported by the Institute for Korea Spent Nuclear Fuel (iKSNF) and the National Research Foundation of Korea (NRF) grant funded by the Korea government(Ministry of Science and ICT, MSIT) (No.2021M2E1A1085200)

How to cite: Lee, Y.-K., Choi, C.-S., and Park, K.-W.: An experimental system capable of bidirectional fluid injection under true triaxial compression conditions for the evaluation of hydro-mechanical properties of natural barriers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6908, https://doi.org/10.5194/egusphere-egu24-6908, 2024.

X4.169
|
EGU24-7072
|
ERE3.3
|
Highlight
Seong Kon Lee, Jihun Choi, In Hwa Park, Myung Sun Kim, Kichang Yang, and Dae-Sung Cheon

To select a suitable site for high-level radioactive waste (HLW) disposal, it is very critical to establish site assessment factors that fit the geological conditions of each country, and suitability of a site as a natural barrier of the disposal system should be evaluated and candidate sites should be narrowed down step by step based on these criteria. Site assessment factors can be largely classified into geological, rock mechanical, hydrogeological, and geochemical properties of the deep geo-environment. In Rep. of Korea, 17 items with 98 assessment factors for site assessment factors are suggested. During the period from 2020 to 2024, eight boreholes were excavated to depths of 750 meters in order to increase understanding of the deep geological environment of Korea. The locations for deep boreholes were selected in the area of Korea's four representative major bedrock types and tectonic structures. Drilling cores were recovered from all boreholes to analyze bedrock geology, and rock mechanical properties, and hydrogeological and hyrdo-geochemical pumping and injection tests were carried out to verify general features of site assessment factors of representative bed rocks found in Korea. Geophysical logging methods are a powerful tool in that one can obtain deep geo-envrionmental properties in a dense manner along the borehole walls and obtaining various site mechanical properties by correlating geophysical well logs with laboratory test results. Geophysical logs generally need recompilation and conversion to acquire suitable site assessment factors, such as dynamic elastic properties of the bedrocks, hydraulic parameters of bedrocks. In this paper, we present systematic method and relevant procedures using geophysical logging data to obtain deep geological environment assessment factors essential for the site selection and characterization for HLW disposal sites. The geophysical logging data are basically carried out through 3-Arm caliper logging; temperature, EC(electrical conductivity) of borehole water, and natural gamma logging; gamma-gamma density logging with dual spacings together with borehole diameter logs; normal resistivity logging together with SP(spontaneous potential), single point resistance, spectral gamma logging (K, U, Th), acoustic televiewer(ATV), and sonic logging with three spacing between a source and 3 receivers. The fracture information are analyzed from ATV amplitude and traveltime to be used to determine data sampling information for hydraulic tests and hydrogeochemical experiments, and p- and s-wave velocities obtained from sonic logging were used to obtain rock mechanical properties for site assessment. The characteristics of the fracture zone shows general trends which are of horizontal in mud stone boreholes and of high-angle dip in crystalline rocks, and shows a clear contrast in hydraulic experiments and hydrogeochemical experiments. All of the above results are merged into the database, D-GIVES(Deep-GeoInformation VErification System) for providing deep geo-environment information on site assessment evaluation, and this is also expected to be used as parameters which are necessary in predicting deep geological environment for long-term safety evaluation.

How to cite: Lee, S. K., Choi, J., Park, I. H., Kim, M. S., Yang, K., and Cheon, D.-S.: HLW site characterization parameters extracted from geophysical well logging data acquired in deep boreholes in Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7072, https://doi.org/10.5194/egusphere-egu24-7072, 2024.

X4.170
|
EGU24-9291
|
ERE3.3
Jens Eckel and Martin Navarro

During the site selection process in Germany, regulated by the Site Selection Act (StandAG), the implementer has to identify adequate siting regions and perform long-term safety analysis for these regions. The Federal Office for the Safety of Nuclear Waste Management (BASE) as responsible federal authority has to review the implementer’s long-term safety analysis. To perform this duty at the required depth, it will be necessary to recalculate important aspects of the analysis by means of numerical computer programs. In addition, this will allow to assess the underlying uncertainties of the implementer’s long-term safety analysis.

Numerical modelling requires a high degree of quality assurance. Therefore, it is important that the same problem is modelled with different computer programs and – if possible – by different teams of modelers. This strategy is known as the diverse modelling approach and forms the basis of regulatory modelling. It can also be implemented within organizations if more than one code is used to tackle the same task.

The diverse modelling approach has been carried out amongst others by the authors over the past two decades by means of the computer programs, TOUGH2-GRS and MARNIE(2). Both (co-)developed programs are thermo-hydraulic codes that compute transport phenomena in porous media and in the case of MARNIE(2) can be coupled to geochemical codes, see [1] and [2] for further details. A recent example for the diverse modelling approach was the use of TOUGH2-GRS and MARNIE for the development of indicators for the safe confinement of radionuclides in a deep geological repository [3].

At the BASE it is planned to further develop and use the open source program PFLOTRAN in the future for the review of long-term safety analysis. PFLOTRAN [4] 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. Amongst other fields of applications, PFLOTRAN has been used to simulate uranium transport at the Hanford 300 Area and is also undergoing qualification for use in performance assessments at the Waste Isolation Pilot Plant (WIPP) [4].

This contribution presents specific repository processes that are part of TOUGH2-GRS and MARNIE but have not yet been completely ported to PFLOTRAN. As an example, we show results from the verification process for anisotropic tortuosities for the diffusive transport of tracers. Another example is the implementation of an effective model for the compaction of salt in the TH part of PFLOTRAN.  These works and the application of PFLOTRAN will strengthen the capabilities of BASE in the independent review process of implementer’s long-term safety analysis within the Site Selection process.

Literature

[1] M. Navarro: User Manual, TOUGH2-GRS Version 2, TOUGH2-MP-GRS Version 0, GRS-505: Köln, 2018.

[2] M. Navarro, J. Eckel et al.: Weiterentwicklung und Qualitätssicherung von Modellierungswerkzeugen zur Durchführung und Bewertung von Sicherheitsanalysen im Standortauswahlverfahren, GRS-622: Köln, 2021.

[3] M. Navarro,  J. Eckel et al.: Indikatoren zur Bewertung des Einschlusses und der Isolation mit exemplarischer Anwendung auf ein generisches Endlagersystem mit dem Wirtsgestein Tongestein, GRS-A-3985: Köln, 2019.

[4] M. Nole et al.: GDSA PFLOTRAN Development (FY2021). United States: N. p., 2021. 

How to cite: Eckel, J. and Navarro, M.: Further development and verification of computer programs for the review of long-term safety analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9291, https://doi.org/10.5194/egusphere-egu24-9291, 2024.

X4.171
|
EGU24-11241
|
ERE3.3
|
ECS
|
Lina Gotzen, Lisa Winhausen, Mohammadreza Jalali, Kavan Khaledi, and Florian Amann

Ensuring the long-term integrity of deep geological repositories for nuclear waste, i.e., safety and sustainability, remains a critical concern for disposal solutions. Reliable predictions on long-term rock mass behavior require a precise characterization and understanding of time-dependent phenomena such as creep and consolidation. While consolidation involves changes in effective stress, creep is characterized by continuous deformation even under minimal to zero effective stress changes. Parameters which describe the drained creep behavior under fully-saturated rock mass conditions and the long-term strength boundaries (i.e., creep failure) of low-permeable clay shales are limited mainly due to the significant amount of time required for laboratory tests. Creep mechanisms may lead to tunnel convergences and delayed failure, but may also favor self-sealing, even under stress conditions below the short-term peak strength. Consequently, a comprehensive understanding of creep mechanisms is necessary for long-term safety analyses and associated precautionary measures.

In this context, we performed hydro-mechanically coupled triaxial creep experiments using samples of the shaly Opalinus Clay obtained from the Mont Terri Underground Research Laboratory in Switzerland. These tests were conducted on fully saturated and consolidated specimens with bedding orientations parallel and perpendicular to the axial loading direction. We applied step-wise, strain-controlled increases in differential stress under drained conditions, succeeded by creep stages at constant effective stresses. Two different multi-stage stress paths were used. The procedure allows observing deformations related to creep mechanisms for different sample geometries and quantifying the influence of the stress path on the creep behavior.

The study findings reveal the occurrence of both primary and secondary creep even at low differential stresses, along with a distinct anisotropic creep behavior related to the bedding orientation. Increased differential stresses generally result in accelerated secondary creep rates, ultimately leading to creep failure below the short-term strength. The strain-rate data allow a subdivision into a stress-insensitive and a stress-sensitive creep behavior depending on the stress conditions, indicating a difference in the dominating creep mechanisms. Our study also shows that the long-term strength and the creep rates depend on the multi-step stress paths. For smaller incremental increases in differential stress, we find a decreased long-term strength and higher creep rates for the same differential stress.

Our results provide insights into the creep behavior of clay shales and yield crucial parameters for incorporating drained creep as a distinct, time-dependent phenomenon into a constitutive model for Opalinus Clay.

How to cite: Gotzen, L., Winhausen, L., Jalali, M., Khaledi, K., and Amann, F.: Time-dependent deformation behavior of Opalinus Clay: A triaxial multi-step creep study under fully drained conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11241, https://doi.org/10.5194/egusphere-egu24-11241, 2024.

X4.172
|
EGU24-12494
|
ERE3.3
|
Jobst Maßmann, Maximilian Bittens, and Vera Noack

The ThermoBase project aims to investigate the thermal field in sedimentary areas in Germany. It was initiated by the Federal Company for Radioactive Waste Disposal (BGE) and motivated by design calculations and safety analyses that are to be carried out as part of the site selection process for a high-level radioactive waste repository. This research project is carried out jointly by the GFZ German Research Centre for Geosciences and the Federal Institute for Geosciences and Natural Resources (BGR). This contribution focuses on stochastic computations from the BGR on the influence of parameters on the transient temperature field in the underground.
Based on research previously completed by the BGR [1, 2], comparative numerical analyses of the temperature distribution for typical geological situations in Germany are conducted. The focus is on the configuration of thermal material parameters, boundary conditions, and the uncertainty in these parameters. Another objective is to investigate the temperature development and penetration depth of permafrost during a possible future glaciation. Statistical methods, such as the Monte Carlo method and stochastic collocation, will be used to make quantitative statements on the impact of changes in these parameters. Methods for the quantification of uncertainties in geological formations related to heat-generating waste repositories [3, 4], which have recently been developed at the BGR and in the joint project MeQur/URS [5], are used here.

Different generic models are intended to be used for this purpose: (1) a 1D-model in which wide parameter variations will be considered, covering a broad range of different rock types, (2) a 2D-model, representing a case study of a repository system in the Lower Cretaceous claystone in northern Germany [1], and (3) a case study of a salt dome in northern Germany, represented by a 2d rotational symmetric model. The salt dome model includes a rock salt sequence within the Zechstein salt layer where the repository is located.

The first results of this work will be presented. Different studies will be shown for the one-dimensional model (1) quantifying the impact of the modeled uncertainties, including global sensitivity analyses. For the two-dimensional model (2), the effect on the temperature distribution of a stochastic state space, defined by uncertain parameters selected based on results from [3], will be demonstrated and first investigations of the 2D salt dome model (3) will be discussed.

References
[1] Maßmann, J. & Ziefle, G. (2017): Integritätsnachweis geologische Barriere. (In: Jobmann, M. et al.: Systemanalyse für die Endlagerstandortmodelle - ANSICHT). Ber.-Nr.: TEC-29-2016-TB; Peine, Hannover, Braunschweig (DBE TECHNOLOGY, BGR, GRS).
[2] Mönig, et al. (2020): RESUS: Synthesebericht. GRS; 567; Köln.
[3] Maßmann, J. et al. (2022): ANSICHT-II – Methode und Berechnungen zur Integritätsanalyse der geologischen Barriere für ein generisches Endlagersystem im Tongestein. BGR, Hannover. DOI:10.25928/n8ac-y452.
[4] Bittens, M., & Gates, R. L. (2023): DistributedSparseGrids. jl: A Julia library implementing an Adaptive Sparse Grid collocation method. Journal of Open Source Software, 8(83), 5003.
[5] Nagel, T, et. al. (2023): MeQur - Uncertainties in THM-coupled integrity calculations, Project web page; URL: https://urs.ifgt.tu-freiberg.de/en/topics/mequr, [Accessed 09-01-2024]

How to cite: Maßmann, J., Bittens, M., and Noack, V.: Statistical analyses on the relevance of thermal data for the safety-related assessment of repository systems - first results from the project ThermoBase, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12494, https://doi.org/10.5194/egusphere-egu24-12494, 2024.

X4.173
|
EGU24-15464
|
ERE3.3
Karsten Reiter, Moritz Ziegler, Oliver Heidbach, Jean Desroches, Erling Fjær, and Silvio Giger

After the upper earth's crust was mainly explored in the last century for the extraction of water, minerals and energy resources, the focus of exploration is increasingly shifting to the temporary storage of energy, the extraction of thermal energy and the disposal of CO2 or radioactive waste. The geomechanical stability of the host rock is particularly relevant for the barrier integrity of a geological repository. The stresses acting on the lithologies and the waste-induced pore pressure evolution determine whether a potential failure can occur. Various methods are used to estimate individual components of the stress tensor on a meter scale. Since the local stress state may be strongly influenced by tectonic structures and spatially variable rock properties, it is necessary to apply 3-D geomechanical models, to predict the spatial distribution of the stress state beyond the in-situ data.

Geomechanical-numerical models require detailed information about the structural composition such as stratigraphic boundaries or faults, and the material properties of the subsurface lithologies. Technically the task is to estimate the equilibrium of forces between gravity and the elastic response due to lateral displacement boundary conditions that result in a best-fit with respect to pointwise stress magnitude data. With the increase in available data, the calibration process becomes more complex, but also provides a framework for testing the validity of the data and the models.

Motivated by the Sectoral Plan Deep Geological Repositories, a comprehensive exploration program was done in three sites in Northern Switzerland between 2016 and 2021, involving 3-D seismic surveys and drilling of nine boreholes. This enabled to refine 3-D geomechanical-numerical models for the potential repository sites. These models differ significantly not only due to the improved geometrical data, but the large number of stress magnitude data and the increased numerical resolution. The presentation is intended to provide an overview of the modelling process, the calibration procedure, the new features of the models and the key results.

How to cite: Reiter, K., Ziegler, M., Heidbach, O., Desroches, J., Fjær, E., and Giger, S.: Enhancements of geomechanical models for potential siting areas in Switzerland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15464, https://doi.org/10.5194/egusphere-egu24-15464, 2024.

X4.174
|
EGU24-15607
|
ERE3.3
Rüdiger Giese, Audrey Bonnelye, Pierre Dick, Carolin Boese, Stefan Lueth, Ben Norden, Katrin Plenkers, Roman Esefelder, Christian Cunow, Liang Pei, and Sven Fuchs

The understanding of the coupled thermo-hydro-mechanical behavior of fault zones in naturally fractured rocks is essential both for fundamental and applied sciences and in particular for the safety assessment of radioactive waste disposal facilities. An international research program called CHENILLE was built to address key questions related to the impact of high temperatures (up to 120°C) on shear zones as well as fault reactivation processes in shale formations. Here, we report on an ongoing thermally controlled in-situ fluid injection experiment on a strike-slip fault zone outcropping at IRSN’s Tournemire Underground Research Laboratory (URL). This includes a series of laboratory experiments to understand the mechanical, hydraulic, structural and thermal evolution occurring within the fault zones during the thermal and hydraulic loading. Reported preliminary results comprise acoustic emission activity and active seismic monitoring results, the thermal diffusion and the temperature evolution measured in-situ with DTS in and around the fault and the corresponding numerical thermal simulation of the experimental setup.

How to cite: Giese, R., Bonnelye, A., Dick, P., Boese, C., Lueth, S., Norden, B., Plenkers, K., Esefelder, R., Cunow, C., Pei, L., and Fuchs, S.: CHENILLE: the fault-heating experiment in the URL Tournemire (France), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15607, https://doi.org/10.5194/egusphere-egu24-15607, 2024.

X4.175
|
EGU24-16144
|
ERE3.3
|
ECS
|
Florian Zill, Tobias Meisel, Christian B. Silbermann, and Thomas Nagel

This study addresses the coupled thermo-hydro-mechanical (THM) modelling of large-scale nuclear waste repositories situated in rock salt. We consider the competing stability requirements arising from different physical processes, such as advection and diffusion in the rock mass surrounding the saline barrier, as well as viscoplastic creep of the latter. Our focus extends to examining potential conflicts between spatial and temporal discretization demands, balancing performance, stability and accuracy. We systematically investigate the applicability of these considerations to a model implemented in OpenGeoSys, aiming to enhance its robustness. 

An essential aspect of evaluating simulation results is analyzing the convergence behavior in the absence of an analytical solution. Several methods exist to extrapolate model results of different discretization to a reference set, such as the Richardson extrapolation. Here, we use such a technique to scrutinize our results, providing a comprehensive assessment of the model's convergence characteristics and the accuracy of the results.

Finally, detailed comparisons across various coupling schemes are conducted for our model, highlighting the impact of implicit process coupling on the model results.

How to cite: Zill, F., Meisel, T., Silbermann, C. B., and Nagel, T.: Dynamics of large-scale THM simulations: numerical considerations for the simulation of nuclear waste repositories in rock salt during glacial cycles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16144, https://doi.org/10.5194/egusphere-egu24-16144, 2024.

X4.176
|
EGU24-17172
|
ERE3.3
|
ECS
Moritz Ziegler, Karsten Reiter, Oliver Heidbach, Jean Desroches, Erling Fjaer, and Silvio Giger

Knowledge of the current undisturbed stress state is a key issue of subsurface applications. Amongst others, the stability of caverns and boreholes depend on the stress magnitudes. For the prediction of the stress in a rock volume 3D geomechanical-numerical models are used. Technically the task is to estimate the equilibrium of forces between gravity and the elastic response due to lateral displacement boundary conditions that result in a best-fit with respect to pointwise stress magnitude data. For sensitivity studies of the effect of variable boundary conditions, the rock properties (Young’s modulus, Poisson ratio, density) are assigned to the corresponding lithologies that are implemented in the model volume. However, mainly the Young’s modulus has a high variability within each lithological unit.

We demonstrate an approach where obtained information on the rock property distribution is included in a geomechanical model to provide several possible stress states. From these individual cases the range of stress states that are likely to be expected are estimated. This results in a bandwidth for the components of the stress tensor. For each component, a median stress magnitude is provided as well as a 1σ and 2σ range. This allows a more comprehensive estimate of the stress state which, in turn, allows to include uncertainties on stress magnitudes in the design of underground structures due to being more informed. Even though, a safety margin will always have to be included, well known and quantified uncertainties may lead to a reduction of said margin. In turn, this improves economic feasibility. The required safety margins can be adapted to the prevailing stress state for each individual unit if potentially unstable zones are identified well in advance.

We demonstrate the applicability of the approach on the site of a planned deep geological repository. The Swiss National Cooperative for the Disposal of Radioactive Waste (NAGRA) provides an unprecedented amount and quality of both stress magnitude and rock property data records for this site. For each unit a cumulative density function of the rock properties is available which allows a robust assessment of the variability. Eventually, we are able to provide a bandwidth of the expected stress magnitudes throughout the model volume. A comparison with the measured bandwidths of stress magnitude data records along borehole trajectories shows a very good agreement between the modelled bandwidth and the range of obtained stress magnitudes.

How to cite: Ziegler, M., Reiter, K., Heidbach, O., Desroches, J., Fjaer, E., and Giger, S.: Spectra of stress: Variability in lithologies represented in geomechanical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17172, https://doi.org/10.5194/egusphere-egu24-17172, 2024.

X4.177
|
EGU24-20864
|
ERE3.3
Alena Sevcu, Petr Vecernik, Rojina Shrestha, Jakub Riha, Milan Kouril, and Veronika Hlavackova

The most used materials in civil engineering is concrete and steel. Their unique properties made them candidate materials for components of engineered barrier system for high- and intermediate-level radioactive waste (ILW and HLW) deposition including material from decommissioning of nuclear power plants. Activated materials include mainly stainless steel of nuclear reactor structural elements or carbon steel and shielding concrete of the reactor shaft construction materials. This study is focused on standard and alternative cementitious matrices for deposition of such activated materials mainly in terms of its long-term sustainability in the presence of microorganisms.

Four different matrices including cement paste based on Ordinary Portland Cement (OPC), cement paste enriched with bentonite or nano-iron, and finally geopolymer, are exposed to conditions that simulate real repository (anaerobic groundwater). One of the objectives is to describe the growth of microorganisms on/in these matrices as a potential risk for the long-term sustainability of such disposal. After a defined time, changes in microbial activity of the matrices, water leachate and interface between matrix and metal coupons simulating activated waste are monitored using cultivation-dependent and independent approach. Here we will demonstrate results of first samplings after 6, 12 and 24 months of incubation in anaerobic conditions. The results will shed more light on evolution of microbial activity in such extreme conditions in time and bring more information on processing and detection of microbial activity in alkaline materials.

How to cite: Sevcu, A., Vecernik, P., Shrestha, R., Riha, J., Kouril, M., and Hlavackova, V.: Microbial activity in Cementitious Matrices for the Storage of Radioactive Waste from the Decommissioning of Nuclear Power Plants , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20864, https://doi.org/10.5194/egusphere-egu24-20864, 2024.

X4.178
|
EGU24-21341
|
ERE3.3
Sarka Sachlova, Vlastislav Kašpar, Petr Večerník, and Michaela Matulová

The Czech national concept of the deep geological repository (DGR) is based on the Swedish KBS-3 concept including an engineered barrier system (EBS) situated in the crystalline host rock. The EBS comprises the double-walled waste disposal package (WDP) embedded in compacted bentonite in vertical drill holes. The double-walled WDP comprises the inner carbon steel package and the outer stainless steel package. Regarding the concept, there was a designed laboratory experiment simulating the thermal and irradiation loading of stainless steel coupons embedded in saturated compacted bentonite.

Four experimental setups were conducted using compacted BCV and MX80 bentonites under anoxic conditions differing in initial saturation level (15-20 wt. %), heating temperature (ambient temperature, 90°C and 150°C), and irradiation (0.4 Gy/h). The analysis of steel samples included: visual inspection, scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD), Raman spectroscopy, and profilometry. Corrosion rate was calculated from the mass loss. The analysis of bentonite samples included: analysis of chemical (X-ray fluorescence microscopy, XRF) and mineralogical (XRD) composition, cation exchange capacity (CEC), and SEM-EDS analysis.

The steel samples embedded in the BCV bentonite heated up at 150 °C indicate a lower corrosion rate when irradiated compared to unirradiated samples. A combination of 150 °C and irradiation leads to surface corrosion indicating an almost constant corrosion rate for the whole testing period. Unirradiated samples heated up to 150 °C showed the highest corrosion rate after 6 months with decreasing tendency when the loading period was prolonged up to 18 months. The decreasing corrosion rate was observed in both irradiated and unirradiated steel samples heated up at 90 °C correlating with increasing loading period. A minimum corrosion rate was found in steel samples embedded in water-saturated BCV bentonite stored under laboratory temperature without irradiation. The inhibiting effect of irradiation on steel corrosion was observed when the steel samples were embedded in MX80 bentonite heated up at 150 °C. Almost no effect of irradiation was observed when the MX80 bentonite was heated up at 90 °C. 

Hematite and Fe-rich carbonates (chukanovite, siderite) were confirmed to form corrosion layers on the steel surface. The thickness of the corrosion layer varied, ranging from 10 to 45 µm, and was directly correlated with the loading duration. Steel samples that remained unirradiated and were heated up at 90 °C exhibited corrosion layers up to 45 µm in thickness after 12 months of loading. In contrast, irradiation and heating up at 150 °C led to the formation of thinner corrosion layers, typically ranging from 10 to 20 µm. The corrosion layer composed of Fe-Si-O was identified only on the surface of steel heated up to 150 °C. The layer was identified only by SEM-EDS indicating amorphous or poorly crystalline structure. The origin of Fi-Si-rich corrosion products needs to be confirmed by future research.

How to cite: Sachlova, S., Kašpar, V., Večerník, P., and Matulová, M.: Characterisation of thermally affected corrosion products originating on steel-bentonite interface, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21341, https://doi.org/10.5194/egusphere-egu24-21341, 2024.