The session covers all waste disposal designs, from (near-)surface over shallow to deep geological repositories. Key topics included in this session are:
• Role of geosciences in site characterisation and selection process
• Features and evolution of natural and engineered barrier systems, including induced effects
• Bio-geo-chemical processes, both natural and repository-induced
• Geoscientific evidence supporting Performance and Safety Assessment
• Long-term evolution studies of interactions among hydro-, geo- and bio-sphere, and their impact on the disposal system
• Radionuclide migration assessment
• Impact of short-term and long-term climate change on waste disposal facilities
• Innovative technologies for site characterisation and monitoring, including digital tools and strategies
Contributions on the above topics can include all aspects covering lab-scale experiments, large-scale investigations in underground research laboratories, information from site characterisation campaigns, studies of natural analogues, data management, review studies, and development and application of digital tools.
Global warming can cause changes in the frequency and intensity of certain types of external natural hazards. In Germany, this particularly affects hydrological and meteorological hazards and hazards derived from them (such as landslides and forest fires). The research project “Impact of Climate Change on the Safety of Nuclear Facilities” (KlimakA) assesses these external natural hazards and their impact on the safety of nuclear power plants, interim storage facilities and a final repository for HLW radioactive waste (during the operational phase).
In this review study various regulations and databases, e.g., VERA/BEVOR, IRS from the IAEA/NEA, INES, VIBS a.o., were evaluated. The focus on these evaluation lies on statements on very rare events (10,000-year events). It became apparent that climate projections are generally only calculated up to the end of the 21st century. Depending on the nuclear facilities under consideration, different time horizons are relevant: while the focus for European nuclear power plants is on the next 60 to 80 years, longer periods extending wide into the 22nd century are of interest for interim storage facilities and a final repository.
The presentation will present the results of the safety assessment of climate change on nuclear facilities and a final repository in the operational phase for HLW waste. Initial assessments indicate that meteorological and hydrological impacts in Central Europe will not change dramatically in the 21st century, with the exception of temperature. Nevertheless, they should be addressed in safety assessments of nuclear facilities, which is also recommended by recent international guidance on climate hazards events. Since interim storage facilities do not rely on active systems to ensure nuclear safety, they are highly robust against such hazards (including changes in them). A final repository could be more vulnerable to extreme meteorological or hydrological hazards during its operational phase. In this context, infrastructure such as lifting equipment and waste conditioning facilities must be protected against climate change. Forecasts are further complicated by the fact that climate forecasts beyond the year 2100 are rare and based on uncertain assumptions.
How to cite: Maurer-Rurack, U., Hellmich, M., Platte, B., Strack, C., and Thuma, G.: Climate Change and its Implications for the repository of HLW in Germany, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7640, https://doi.org/10.5194/egusphere-egu26-7640, 2026.
The assessment of future dissolution rates is an important aspect in the long-term forecast of the evolution of a salt dome, as a potential host rock for a nuclear waste repository. Dissolution or leaching occurs under the influence of undersaturated groundwater on saline rocks. In this way, dissolution reduces the thickness of salt formations and could be significant for the thickness of the host rock. Higher dissolution rates are possible, on the one hand, with continuous salt rise or regional uplift with erosion of the overlying rock. On the other hand, higher dissolution rates can occur with saline solutions flowing away from the area of the salt level due to groundwater flow, for example, through the formation of fractures in the cap rock and overlying rock and the resulting altered permeability. Hydrogeological conditions could change in the future due to altered climatic conditions (higher groundwater recharge rates) and affect dissolution.
This project intends to deepen the understanding of the conditions under which dissolution occurs at the salt interface and to determine dissolution rates depending on the hydrogeological conditions caused by climate. This is done through the simulation of different boundary conditions over time. Different climatic developments for the next 150,000 years are defined. These are meant to cover the two extremes, namely a warm period with no cold period and an early onset of a cold period, as well as certain glacial configurations, such as direct ice coverage or a glacier margin, and variations regarding a tunnel valley and the formation and depth of permafrost. The aim is to investigate how changes in hydrogeological conditions under different climatic settings affect dissolution rates at a salt dome, or whether dissolution occurs at all. An existing generic 2D geological model of a salt dome with overlying rock is adapted to the respective question, meaning, for example, that in the case of considering the impact of a tunnel valley, the existing model is geometrically modified to incorporate a tunnel valley with infill as a structure. Variable fluid viscosities around the salt dome due to variations in salinities and temperature will be considered. Furthermore, the impact of more permeable transition zones in between the salt dome and adjacent units will be analysed. We show here the set up of the 2D geological model and defined scenarios for the simulation.
Resulting dissolution rates can be scaled to the observation period of 1 million years based on assumptions about climatic development to determine maximum dissolution rates.
How to cite: Schütz, F. and Bebiolka, A.: Model Set-Up to Determine Dissolution Rates at a Salt Dome under Changing Climatic Conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10152, https://doi.org/10.5194/egusphere-egu26-10152, 2026.
With the growing global demand for energy and the transition toward low-carbon sources, nuclear power is expected to play a key role in the foreseeable future. However, nuclear power generation produces high-level radioactive waste (HLW) that requires safe, long-term isolation from the biosphere. Currently, HLW is stored in surface facilities, while several countries (e.g., Finland, USA, Sweden, France, Switzerland) are developing mined geological repositories at depths of 500–1000 m.
This study is related to Ultra Deep Disposal in a borehole at kilometers depth. TNO is investigating a concept for large-diameter borehole disposal of HLW at depths of ~5000 m. Ultra-deep disposal offers several potential advantages over mined repositories: enhanced isolation, reduced migration risk, and lower costs. At these depths, waste is placed at great distance to the biosphere well below fresh groundwater resources, relying on both the thickness of overlying strata and the sealing properties of host rocks as natural barriers,
A robust geological safety case for ultra-deep disposal requires evaluation of multiple criteria, including barrier integrity, mechanical and geological stability, and subsurface usage. A key safety factor is the prevention of degradation of the engineered barriers and radionuclide migration —the primary mechanism for containment failure. At ultra-deep levels, stagnant formations significantly reduce fluid transport potential. Without fluid transport, engineered barriers, canister degradation and radionuclide transport are negligible, ensuring long-term safety.
Faults represent potential migration pathways; however, many faults act as sealed fluid traps due to juxtaposition mechanisms, as extensively studied in hydrocarbon systems. Importantly, fault sealing behavior differs fundamentally between crystalline and sedimentary environments. In crystalline rocks, faults often remain open because deformation is dominated by brittle fracturing, making them potential conduits. In contrast, plastic deformation in sedimentary environments results in sealing of faults through clay smear, shale gouge, and cementation, enabling faults to act as effective barriers.
This research focuses on assessing fault connectivity within the Namurian (Upper Mississippian–Lower Pennsylvanian) as one of the potential host formation for ultra-deep disposal. Preliminary work involves analyzing fault geometry and structural characteristics to identify zones of potential connectivity and sealing capacity. These insights will inform future modeling of fault behavior and its role in long-term containment for Ultra Deep Disposal.
Results indicate that faults in the study area, under the conditions examined, are not necessarily migration pathways. They can function as additional barriers, enhancing the geological containment system for ultra-deep disposal.
How to cite: Altenburg, R. and Heerens, G.-J.: Ultra Deep Disposal: Evaluating Fault Behavior for Long-Term Nuclear Waste Containment at 5000 m depth, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17195, https://doi.org/10.5194/egusphere-egu26-17195, 2026.
Establishing a robust geoscientific foundation is essential for the long-term safety of radioactive waste repositories. However, public acceptance remains a significant challenge for the siting of radioactive waste storage and disposal facilities. A strategic approach to mitigate this challenge involves the co-location of diverse management operations within a single site. This study explores this potential by developing a conceptual framework for an offshore island in the Taiwan Strait, targeting the Mesozoic basement as the host rock.
This study develops a 3D geological model using JewelSuite, integrating disparate datasets including geological surveys, seismic reflection profiles, and deep borehole logs to define key stratigraphic interfaces. Based on this structural framework and hydraulic parameters derived from literatures, 3D groundwater flow simulations were implemented using DarcyTools to assess the hydraulic performance of the site. The simulation outputs provide critical insights into the spatial distribution of hydraulic pressure and flow velocity within potential host formations.
These hydrogeological results serve as a primary reference for the conceptual design and spatial configuration of subsurface engineering. By bridging geoscientific characterization with engineering layout, this research proposes a comprehensive conceptual framework for an integrated subsurface complex. This includes a generic Underground Research Laboratory (URL), underground interim storage, and a combined repository for high-level and low-level waste. Distinct from the crystalline rock geological disposal concepts currently prioritized in Taiwan, this study focuses on Mesozoic basement rocks as the geological foundation. The proposed framework demonstrates the technical viability of an offshore co-located solution, providing a critical alternative option for Taiwan's national radioactive waste disposal strategy.
How to cite: Chen, L.-G., Lin, C.-C., Lin, T.-S., and Tseng, H.-H.: Integrated Subsurface Modeling and Co-location Concept for Offshore Radioactive Waste Management: A Case Study of Mesozoic Basement in the Taiwan Strait, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2701, https://doi.org/10.5194/egusphere-egu26-2701, 2026.
For the assessment of the long-term safety and geological stability of sites foreseen for deep geological repositories for radioactive waste, it is essential to understand the hydrogeochemical evolution of regional deep aquifers. They represent the boundary conditions for the geological barrier and represent potential exfiltration pathways for radionuclides that may be released from the repository in the far future.
Here we present highlights of hydrogeochemical data and their interpretation collected during Nagra’s recent deep drilling campaign performed in the context of the site selection process for the Swiss deep geological repository. The extended hydrogeochemical investigation included groundwater and porewater hydrochemistry, rock properties, hydrotests, porewater tracer simulations, and groundwater modelling. For groundwaters, essentially all currently available analytical techniques for major ions, trace elements, stable and radiogenic isotopes, as well as common and noble gases were applied. Combining information from all these analyses allows to demonstrate that the aquifers above and below the Opalinus Clay host rock experienced a highly distinct, aquifer-specific evolution and do not hydraulically communicate across the geological barrier. For instance, groundwater in the Malm limestone aquifer located above the host rock contains a 16-20 Ma old marine Na-Cl signature and displays high salinities and 81Kr model ages of up to 15 g/L and 600 ka, respectively. Hence, it behaves almost like a stagnant water body with very low flow rates, which is due to the low permeability and the lack of major open karst features and highly transmissive faults.
In contrast, groundwater in the Muschelkalk dolostone aquifer located beneath the host rock represents a more dynamic flow systems with generally lower salinities and residence times. Nevertheless, two distinct components of different age and hydrochemical signatures can be distinguished. The first one represents a hydrochemically evolved groundwater with elevated concentrations of Na, Cl, and Li, indicative for rock salt dissolution and/or minor interaction with the underlying crystalline basement. The second component is of the Ca-SO4 type and shows a clear glacial water stable isotope signature. Based on the spatial distribution of hydrochemical parameters, we infer that recharge of this glacial component occurred during a short period of time after the last glacial maximum. We link this glacial component to the deflection of the Wutach river towards the recharge area of the aquifer about 18 ka ago. The deflection forced the Wutach to flow directly across the outcrops of the Muschelkalk aquifer for a few thousand years, thus strongly increasing the recharge rate of glacial meltwater into the aquifer.
The two examples emphasize that extended hydrochemical investigations during site characterization may allow to unravel regional scale hydrochemical evolutions of deep aquifers on the time-scale of up to several million years. For the example of the Swiss program, the extended hydrochemical investigation significantly contributed to demonstrate the long-term geological stability of the site.
How to cite: Wanner, C., Kiczka, M., Stopelli, E., Traber, D., Heidinger, M., Waber, H. N., Kerrou, J., Schwanghart, W., Landgraf, A., and Schnellmann, M.: Groundwater circulation in deep aquifers in Northern Switzerland: Lessons learned from Nagra’s deep drilling campaign, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9796, https://doi.org/10.5194/egusphere-egu26-9796, 2026.
During the siting process the Swiss radioactive waste management organisation Nagra completed nine drillings through the Jura fold-thrust-belt and its evaporitic detachment, mostly down to the underlying basement. A total of around 5.5 km of oriented cores were recovered providing a unique basis for structural analyses. We use this data to review and amend the tectonic history of the wider region of the easternmost Jura which also comprises the site of the future deep geological repository for nuclear waste.
Based on the structural core analysis we characterise the kinematics of four main deformations: (1) a NNW-SSE-extension, which is unequivocally dated to the Jurassic and related to the rifting of the European margin during the opening of the Penninic ocean, (2) a NNW-SSE-extension by the Paleogene-Neogene flexure of the Molasse foreland basin, (3) a local NE-SW extension correlated to the formation of nearby Paleogene-Neogene graben systems, and (4) Neogene (21 Ma) to Quaternary heteroaxial SSE-NNW- and SSW-NNE-directed shortening. Repeated changes of shortening directions probably relate to strain partitioning in a zone of oblique convergence. Convergence at oblique angles with respect to pre-existing basement faults is partitioned into mild sinistral-transpressive shear parallel to the prevailing basement faults and orthogonal shortening perpendicular to these faults.
The outlined tectonics of the last about 21 Ma allows a qualitative extrapolation into the tectonic future of the planned repository considering the past processes as key information for possible future evolutions. Past tectonic history provides sound evidence for pre-dominant concentration of deformation along pre-exisiting faults with aforementioned possible changes in shortening directions. Future tectonic scenarios that can be expected include switches of the deformation regime between orthogonal shortening and sinistral transpression, and changing stress/strain coupling and decoupling between the allochthonous units and the units below the basal evaporitic detachment. However, it should be noted that the site selection process has identified a region that has seen very little deformation in the past. At the site larger faults have been carefully delineated with 3D-seismics and by avoiding these zones the repository is expected to remain intact even in the case of re-activations of regional faults.
How to cite: Decker, K. and Schneeberger, R.: Forecasting the tectonic evolution of the Swiss Jura fold-and thrust belt: Structural analyses of oriented cores from deep exploration boreholes for the Swiss radioactive waste disposal, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18412, https://doi.org/10.5194/egusphere-egu26-18412, 2026.
Robust geological site selection for deep geological repositories relies on an interrelated understanding of stratigraphy, structure, and hydrogeology, particularly the capacity of low-permeability formations to contain fluids and solutes over geological timescales. Argillaceous formations such as the Opalinus Clay are therefore intensively studied as potential host rocks for radioactive waste disposal. However, their role within the wider hydrogeological framework of entire sedimentary successions remains insufficiently constrained. A key issue concerns the holistic hydrogeochemical characterization of containment zones and their effectiveness in preventing radionuclide migration across formation boundaries.
The Mont Terri Underground Research Laboratory in Switzerland, with over three decades of multidisciplinary research on the Opalinus Clay, provides a unique natural laboratory and infrastructure to investigate these questions. The DEBORAH (Deep Borehole to Resolve the Mont Terri Anticline Hydrogeology) project—the deepest drilling project to date at the Mont Terri site—offers the opportunity to complement previous extensive local studies on the regional scale encompassing the full stratigraphic succession of the Mont Terri anticline.
DEBORAH aims to systematically sample and quantitatively characterize the geological system in and around the Opalinus Clay. The project integrates: (A) an approximately 800 m deep, fully cored underground borehole from the St-Ursanne Formation down to the Schinznach Formation, including dedicated hydrogeochemical porewater sampling, in-situ downhole testing, and geophysical core and downhole logging; (B) seismic reflection and tomography studies combining surface, tunnel, and downhole acquisition geometries to image the geological structure of the Mont Terri anticline; and (C) hydrogravimetric monitoring of natural fluid migration in aquifers above the Opalinus Clay.
The resulting datasets will support 3D geological, hydrogeological, and reactive transport modelling, enabling improved quantification of hydraulic connectivity and containment within and across the system. Beyond Mont Terri, DEBORAH seeks to develop transferable in-situ investigation workflows to support future site selection procedures for radioactive waste disposal in Germany and elsewhere, thereby advancing best practices in scientific continental drilling and subsurface safety assessment. In particular, the realization of a deep borehole in the exceptionally well-characterized geological setting at Mont Terri is likely unique worldwide and will provide critical insights into what can be learned about repository site selection from a single exploration borehole.
How to cite: Kästner, F., Jaeggi, D., Kühn, M., Lüth, S., and Güntner, A.: Unveiling the Hydrogeology of the Mont Terri Anticline – Insights from the DEBORAH Deep Drilling Project, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17375, https://doi.org/10.5194/egusphere-egu26-17375, 2026.
The Radioactive Waste Repository Authority (SÚRAO) is the national organisation responsible for the safe management and disposal of radioactive waste in the Czech Republic. One of the key components of its long‑term mission concerns the development of the country’s deep geological repository (DGR), which is currently advancing via a structured programme of research, design and stakeholder engagement. Aimed at supporting the pre‑implementation phase, SÚRAO is currently conducting an extensive research, development and demonstration (RD&D) programme using a number of generic underground research laboratories, which provide the experimental conditions required to verify the repository concept prior to the selection of the final site (Smutek et al., 2023).
The Bukov Underground Research Facility (URF), including its recent extension - Bukov URF II, fulfils a central role in the RD&D framework. The facility is situated on the 12th level of the former Rožná I uranium mine, approximately 500 metres below the surface. Bukov URF II consists of 6 laboratory corridors and a total of 13 test chambers. The excavation of the Bukov II galleries was completed in April 2024, and the facility entered operation in 2025.
The geological and geotechnical characterisation of Bukov URF II is focusing on forming an understanding of the structural, lithological, hydrogeological and mechanical properties of the Moldanubian crystalline rock basement. Recent investigation research - including detailed structural mapping, core logging, hydrogeological tests, geophysical surveys and in‑situ stress measurements – has provided the data required to make a high‑resolution assessment of the rock mass. The data form the basis for designing and evaluating repository‑relevant experiments, including the testing of the engineered barrier system and the validation of the technical design of the DGR (Hausmannová et al., 2025). The comprehensive results assist in further refining the understanding of deformation structures, fracture network connectivity, geomechanical behaviour and rock mass quality across the newly-excavated spaces of Bukov URF II (Bukovská et al. 2025). Together, these findings significantly strengthen the evidence base for the Czech DGR programme and its continued technical development.
References:
Bukovská Z., Soejono I., Rukavičková L., Chabr T., Morávek R., Levý O., Sosna K., Souček K., Vavro M., Řihošek J., Zelinková T., Pořádek P., Švagera O., Kryl J., Hanák J., Čermák F., Kašpar R., Mareček L., Nedvěd J., Vavro L., Staš L., Georgiou L., Janeček I., Zuna M., Kočan K., Třískalová I., Velímková A. (2025): Geological and geotechnical characterisation of the rock environment – Bukov URF II – English summary. – TZ812/2025/ENG, SÚRAO, Prague.
Hausmannová L, Augusta J. Dohnálková M., Golubko A., Lahodová Z., Matušková E., Mecová M., Smutek J., Valter M., Vencl M. (2025): Technical design of the deep geological repository 2025, SÚRAO TZ 848/2025/ENG REV.1, Prague.
Smutek J., Augusta J., Dohnálková M., Golubko A., Hausmannová L., Mareda L., Matulová M., Mikláš O., Vondrovic L. (2023): The Bukov URF research, development and demonstration activities programme 2023. TZ 683/2023/ENG, SÚRAO, Prague.
How to cite: Klištinec, J., Smutek, J., Soejono, I., Švagera, O., and Golubko, A.: Bukov URF II – the new section of the operated Czech generic underground research laboratory: selected results from construction‑phase characterisation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19658, https://doi.org/10.5194/egusphere-egu26-19658, 2026.
Natural analogue studies provide valuable constraints for long-term assessment of deep geological repositories by examining subsurface environments analogous to repository settings. In South Korea, a natural analogue site in Boeun consists of a black slate with two U-rich coaly slate layers. In this study, we conducted an integrated hydraulic characterization of the fractured aquifer to improve understanding of groundwater flow and solute transport, thereby providing a hydrogeological basis for geochemical interpretation and key constraints for subsequent flow–transport modeling. The characterization was based on one borehole and three wells with depth-discrete open intervals. In specific, we integrated borehole logging (e.g., electrical conductivity (EC) profiling, optical borehole imaging (OBI), and flowmeter logging) with hydraulic tests, including slug, pumping, and solute tracer tests. EC profiling reveals depth-stratified groundwater intervals with distinct chemical signatures. OBI indicates pervasive fracturing throughout the borehole, but the fracture aperture varies with depth. Flowmeter logging identifies hydraulically active intervals that closely match the depth where OBI suggests larger apertures, supporting a depth-dependent hydraulic structure consistent with the EC profile. Consistent with the logging results, slug and pumping tests show modest vertical variability in hydraulic conductivity, supporting depth-dependent differences in hydraulic contributions across the borehole intervals. Tracer tests designed based on the integrated logging and test results suggest reduced vertical hydraulic connectivity across the interval separating the two coaly slate layers, implying compartmentalization and weakened connectivity between the stratified groundwater intervals. Based on these findings, we will develop a discrete fracture network-based conceptual model and incorporate it into coupled groundwater flow and transport simulations to enhance the predictive reliability of radionuclide behavior predictions at the natural analogue site.
This work was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Education (RS-2025-25414628) and the Korea government (MSIP) (NRF-2021M2E1A1099413).
How to cite: Ha, S.-W., Baek, J.-Y., Kim, Y. J., Lee, S.-S., and Lee, K.-K.: Integrated Hydraulic Characterization of a Fractured Aquifer at a Natural Analogue Site for Radioactive Waste Repositories in South Korea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4569, https://doi.org/10.5194/egusphere-egu26-4569, 2026.
Oxidation-reduction (redox) conditions are among the key factors affecting the long-term safety of nuclear waste disposal. In Finland and Sweden, where high level nuclear waste will be deposited at a depth of 400-450 m in crystalline bedrock, underground repositories are estimated to become anoxic within 200 years after closure (King et al 2010). This scenario follows the general understanding of biological and abiotic consumption of photosynthetic oxygen in the subsurface but does not consider possible in-situ oxygen production. However, non-photosynthetic oxygen is known to be produced by microbiological dismutation reactions and radiolysis of water even under the dark conditions prevailing in the deep subsurface (e.g., Ershov & Gordeev, 2008; Ruff et al. 2023). Such continuous supply of oxygen in deep groundwater environments can greatly influence the long-term safety of nuclear waste disposal, as corrosion reactions, microbial activity, and the mobility of uranium and other redox sensitive elements are strongly affected by the availability of oxygen.
In our study, we investigated dissolved oxygen concentrations and isotopic composition, microbial communities and their metabolic pathways, as well as reaction thermodynamics to reveal dark oxygen production and potential for oxic niches in deep (> 125 m) bedrock groundwaters in Finland. Our results show that oxygen is commonly found in the deep subsurface, its isotopic composition differs from that of atmospheric air, and deep microbial communities contain genes for protection against oxygen radicals and oxygen-dependent metabolic pathways. Reactions involving oxygen are thermodynamically favored, which would suggest rapid consumption of oxygen. However, their progression is constrained by the availability of other reactants or the accumulation of reaction products, and therefore only a subset of oxygen-driven reactions is energetically feasible in the deep subsurface, potentially allowing the development of oxic niches. Considering these results, redox conditions in the deep subsurface should be reevaluated.
References
Ershov, B. G. & Gordeev, A. V., 2008. A model for radiolysis of water and aqueous solutions of H2, H2O2 and O2. Radiation Physics and Chemistry 77, 928-935.
King, F., Lilja, C., Pedersen, K., Pitkänen, P., Vähänen, M., 2010. An update of the state-of-the-art report on the corrosion of copper under expected conditions in a deep geologic repository. SKB-TR-10-67, Swedish Nuclear Fuel and Waste Management Co., 176 p.
Ruff, S. E., Humez, P., Hrade de Angelis, I., Diao, M., Nightingale, M., Cho, S., Connors, L., Kuloyo, O. O., Seltzer, A., Bowman, S., Wankel, S. D., McClain, C. N., Mayer, B., Strous, M., 2023. Hydrogen and dark oxygen drive microbial productivity in diverse groundwater ecosystems. Nature Communications 14, 3194.
How to cite: Kietäväinen, R., Kuusiluoma, M., Hapuhinna, I., Nuppunen-Puputti, M., Nyyssönen, M., and Bomberg, M.: Unexpected oxygen calls for rethinking redox conditions in deep geological repositories, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7044, https://doi.org/10.5194/egusphere-egu26-7044, 2026.
In many deep geological repository (DGR) concepts for the storage of high-level radioactive waste, bentonite clay is planned to serve as a buffer material between the host rock and the canister. It is expected to serve both a chemical role (immobilization of radionuclides) and a biological one, the inhibition of microbial growth and activity. Sulfate reducing bacteria (SRB) are of particular concern due to the production of sulfide, a strong steel-corroding agent. It is conventionally assumed that microbial sulfate reduction in the bentonite buffer may become active only once oxygen in a DGR is depleted, and that at that stage, compacted bentonite will physically inhibit microbial activity. Here, we challenge this view by showing that a subset of SRB present in the bentonite backfill and in the host rock under repository-relevant conditions are adapted to tolerate, and transiently exploit, oxygen and pore space before the backfill is fully anoxic and saturated. These results are from an in-situ incubation experiment (1.5 and 3 years) conducted in a borehole in Opalinus Clay using modules filled with compacted Wyoming bentonite (1.25 g/cm3) and containing carbon steel coupons. To investigate the role of oxygen, bentonite was pre-equilibrated with an atmosphere containing 0%, 21%, or 100% O₂ prior to deployment. Mineralogical and chemical analyses of the buffer were combined with corrosion studies and microbial assays to assess the response of SRB to oxygen and its consequences. We find that oxygen drives the enrichment of bacteria, including SRB, at the bentonite–host rock interface, most likely during early saturation, when oxygen is still present and the pore space allows for microbial colonization from the borehole. This enrichment leads to sulfide production and reduction of structural Fe(III) in montmorillonite, locally affecting buffer composition, but has a negligible impact on carbon steel corrosion. In the long term (here, 3 years), the oxygen-stimulated effect becomes less important for microbial abundance, which declines; however, sulfate reduction at the boundary remains active. These findings provide a more realistic view of early-stage microbial dynamics at the host rock–backfill boundary and their limited but non-negligible impact on buffer and canister stability in the presence of unavoidable initial oxygen.
How to cite: Jakus, N., Kulkarni, P. V., Grolimund, D., Mischler, S., Diomidis, N., and Bernier-Latmani, R.: Transient oxygen-driven microbial activity at the bentonite–host rock boundary, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12370, https://doi.org/10.5194/egusphere-egu26-12370, 2026.
Within the framework of the LTD project (NUMO - Japan, SURAO - Czech Rep., NAGRA – Switzerland, BASE - Germany), a dipole tracer test was performed in the GAM shear zone at the Grimsel Test Site. The granitic rock at Grimsel is characterized by the presence of ductile shear zones with thicknesses ranging up to meter scales, which in turn include intensely deformed mylonitic bands with thicknesses up to several tens of centimeters. Brittle fractures (mm scale) developed in late stages of deformation, mainly in the mylonite bands, and are partially filled by a highly porous fault gouge.
The experimental setup included two boreholes (injection and extraction) which intersected the shear zone. The distance between the two boreholes along the shear zone was 1.2 m. In the first part of the experiment, Grimsel groundwater containing the tracers was injected at 1 mL/min during 20 hours, followed a long period (> 1 year) of injection of groundwater without tracers. Extraction in the second borehole was continuously performed at the same rate of 1 mL/min together with monitoring of tracer concentrations. The tracers were 3H as HTO (conservative), 22Na (weakly-sorbing) and uranine (only for early on-line monitoring). In the second part of the experiment, not discussed here, injection was repeated using strongly sorbing 134Cs and 133Ba, together with uranine. Overcoring for rock sampling took place shortly after the end of the second tracer injection.
The breakthrough curves (btc) for HTO and 22Na showed very well defined tails, with different slopes in log-log space for HTO (-2.0) and 22Na (-1.5). While the slope for 22Na is that typical for diffusion from the rock matrix back to the fracture, the one for HTO could in principle be attributed to heterogeneous advection. To check this hypothesis, the tests were modeled accounting for fractures with different apertures within the shear zone. First, an analytical solution for the one-dimensional advection-dispersion equation was used to model the results for HTO. Calculations were performed for twenty different fracture apertures following a truncated Pareto distribution. Flow in the fractures was distributed according to the cubic law, with a fixed total flow rate of 1 mL/min.
Once the results for HTO could be reproduced with the analytical model, it was applied in a numerical 2D model, including flow along the fractures and diffusion in the rock matrix. The slope of the tails of the btc’s could be then explained by the addition of the individual btc’s from the different types of fractures. For HTO, the peaks of the individual btc’s have a much stronger weight than the tails, due to the small rock capacity factors (non-sorbing tracer), resulting in the overall slope of -2.0. For 22Na the tails have much stronger weights (larger concentrations), due to the larger capacity factors, producing the overall slope of -1.5 typical of matrix diffusion.
How to cite: Soler, J. M., Figueira, M. A., Saaltink, M. W., Lanyon, G. W., and Martin, A. J.: Modeling of a dipole matrix diffusion test at the Grimsel Test Site. What explains the different slopes of the tails of the breakthrough curves?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-320, https://doi.org/10.5194/egusphere-egu26-320, 2026.
Radioiodine (129I) poses a long-term environmental and health risk due to its high mobility, solubility, radiotoxicity, and long half-life. Owing to chemical similarities between iodine species and other anions accommodated in apatite, this mineral represents a promising host for radioiodine immobilization. Nevertheless, the mechanisms of iodine incorporation into the apatite structure remain insufficiently understood. In this study, we evaluated the immobilization of iodate by Cl-OH and hydroxyapatite under hydrothermal conditions. Experimental solids were characterized using electron microprobe, scanning electron microscopy, X-ray diffraction, synchrotron X-ray absorption spectroscopy, and atom probe tomography. Experimental solutions were analyzed by ultraviolet–visible spectrophotometry and ion chromatography. The highest iodate concentration measured in apatite was 6.0 wt.% when a 0.1 M NaIO₃ solution was used as the crystal growth medium. However, the ratio of iodate incorporated into the solid relative to its concentration in solution increased with decreasing aqueous iodate concentration, indicating enhanced compatibility of iodate within apatite at ppm-level aqueous concentrations. These results suggest that iodate may substitute for both phosphate and hydroxyl (or chloride) in the apatite structure.
How to cite: Gabitov, R., Laird, W., Jimenez, A., Perez-Huerta, A., Migdisov, A., Jernej, J., Dietzel, M., Guo, X., Xu, H., and Rhee, H.: Iodate Incorporation into Apatite: An Experimental Study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14251, https://doi.org/10.5194/egusphere-egu26-14251, 2026.
The adsorption of radionuclides (RNs) onto mineral surfaces is a key retardation mechanism and plays a critical role in the long-term safety assessment of radioactive waste repositories. While numerous studies[1,2,3] have investigated the sorption behavior of trivalent actinides (e.g. Am, Cu) and lanthanides (e.g. Eu, Y) on various minerals, most experiments rely on geochemically simplified systems, typically in binary configurations involving single minerals and single sorbing species. Natural systems, however, are considerably more complex, with competitive sorption, bulk and surface precipitation, incorporation, and co precipitation processes all influencing RN retardation.
In this study, we examine the competitive sorption of Eu (a chemical analogue for trivalent actinides) and Al onto quartz using a combination of batch and column experiments supported by mechanistic surface complexation modeling (SCM). Aluminum, an abundant component in natural groundwater and porewater, may compete with RNs for sorption sites. In addition, due to its low solubility at near neutral pH, Al may undergo surface precipitation, altering mineral surface charge and modifying sorption behavior.
Batch experiments were performed under varying geochemical conditions, including pH, ionic strength, and initial Al and Eu concentrations. The results show that Al sorption onto quartz arises at lower pH compared to Eu, with sorption edges at approximately pH 4.5 for Al and pH 5.5 for Eu (50% sorbed). In the presence of Al, Eu sorption onto quartz is significantly reduced. Batch sorption data is used for SCM calibration via inverse modeling. These models are then validated using experimental data from column experiments to assess the applicability, advantages, and limitations of derived parameters. In addition, column experiments with K‑feldspar are planned and will be evaluated using SCM to further examine competing sorption effects. Ongoing work focuses on further model development. First modelling outcomes, together with initial assessments of the applicability, strengths and limitations of the emerging parameter set will be presented.
These investigations contribute to improving previous modelling approaches in which competitive Al sorption may have influenced radionuclide behavior. More broadly, the results highlight the importance of understanding geochemical surface reactions to enhance the reliability of long-term safety assessments for radioactive waste repositories.
[1] J. Neumann, J. Colloid Interface Sci. (2020) (https://doi.org/10.1016/j.jcis.2020.11.041)
[2] J. Lessing, Colloids and Surfaces A (2024) (https://doi.org/10.1016/j.colsurfa.2024.133529)
[3] S. Britz, PhD Thesis, 2018 (https://doi.org/10.24355/dbbs.084-201806051207-0)
How to cite: Fricke, J., Britz, S., Kozlowski, A., Lützenkirchen, J., Hosseinimonjezi, B., and Lessing, J.: Competitive sorption effects of Al on the retardation of Eu by quartz and K-feldspar: Experimental and mechanistic modelling insights, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-23080, https://doi.org/10.5194/egusphere-egu26-23080, 2026.
The digital twin (DT) concept has recently attracted attention also in radioactive waste management (RWM). However, its current development and application, particularly in the field of radioactive waste disposal, are at an early stage as compared to other disciplines and industrial branches, such as the nuclear sector, manufacturing and healthcare. Therefore, a dedicated work package within the EJP EURAD-2 project (European partnership on radioactive waste, www.ejp-eurad.eu) was dedicated to DT. The EURAD-2 DITOCO2030 (Digital Twins (DT) to support Optimisation (including communication of safety), Construction and Operation of radioactive waste management facilities) work package aims to develop a roadmap to bridge the existing R&D gap between the currently fragmented DT applications across individual disciplines (e.g., engineering, safety, geology, infrastructure development) as well as data management systems and decision-making platforms. Digital twins can be developed for specific components as well as for the whole geological disposal facility of which the geological environment is an essential part in the safety approach.
The work began with an overview of current practice, combining insights from the RAW community with relevant experience from other industries and research domains, and translating this knowledge to the context of nuclear waste management. Building on this foundation, gap analyses were performed to identify key gaps and opportunities, informing strategic recommendations for future digital twin (DT) development with a particular focus on end-user requirements. A specific challenge for a geological disposal ensuring the correct representation and setting of the underground engineering structures in a geological environment. This requires a combination of geological, hydrogeological, geochemical and geotechnical concepts, models and data via a geographic information system (GIS) and those related to building information modelling (BIM) as well as the coupling of BIM with numerical solvers for the physical modelling of repository components to facilitate the optimisation of the repository design. Considering geological systems, further difficulties are posed by the complexity of geological structures, strong coupling of THMC processes as well as uncertainties at different spatial and temporal scales. The presentation will - outline strategic pathways for DT development and identify high-value research opportunities, with particular focus on the geological environment and its role in shaping disposal system performance and long-term safety. The proposed directions are grounded in end-users needs, and are intended to deliver actionable recommendations that support practical decision-making.
How to cite: Szőke, R., Jacques, D., Laikari, A., Baksay, A., Cayón, P., Papafotiou, A., and Roman-Ross, G.: Enabling Digital Twins for geological radioactive waste disposal – Insights and recommendations from EURAD-2 DITOCO2030, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10080, https://doi.org/10.5194/egusphere-egu26-10080, 2026.
The use of seismic waves is well established in geophysics and geotechnical applications, particularly through surface-wave analysis, seismic reflection, and refraction methods. However, their use as a communication medium for data transmission remains uncommon, especially in deep geological environments where electromagnetic communication is strongly attenuated. However, this wireless communication method represents an interesting opportunity for underground infrastructures such as radioactive waste repositories, particularly for long-term monitoring. In this context seismic waves play an alternative role for long-term wireless underground communication. This study investigates the feasibility of transmitting digital information such as an image through geological layers using seismic waves. Experiments were conducted at the Andra Underground Research Laboratory (URL) to transmit encoded data for the first time from 490 m depth to the surface. The experimental setup consisted of 30 geophones deployed on the surface and two seismic source locations in the URL (borehole and on tunnel floor). The signals were generated from a depth of 490 meters to the surface by using a SeisMovie seismic source which is a low energy piezoelectric vibrator. The experimental setup generated stable and repeatable seismic signals, enabling reliable time-frequency analysis. Several encoding and decoding schemes were tested, including Hamming (7,4) code, frequency modulation, and Morse code. The analysis presented here focuses on the transmission of a 11x17 pixel image encoded using the Hamming (7,4) code. Each pixel was converted into a sequence of frequency activations and transmitted as seismic signals to the surface. The selected frequency band range from 103-124 Hz, corresponding to approximately 20-25 wavelengths for a P-wave velocity of 2500 m/s. Time-frequency analysis of the surface recordings enabled identification of the transmitted frequencies, which were then detected through threshold-based detection. Followed by Hamming decoding, this process successfully reconstructed the transmitted image. For a single transmission, only eight pixels out of 204 were incorrectly decoded, demonstrating the robustness of the encoding and detection workflow under realistic underground conditions. To assess repeatability and signal stability, the same experiment was repeated five times. Stacking the five recordings increased the signal-to-noise ratio by a factor of √5, significantly improving frequency detection. In the stacked case, only one pixel was incorrectly reconstructed, with 90% of the pixels decoded correctly without requiring error correction. The Hamming (7,4) code played an important role in correcting single-bit errors, particularly for individual transmissions with lower signal-to-noise ratios. The main limitation of the current workflow is the use of a fixed detection threshold, which does not fully account for amplitude variability due to noise or source performance. Future work will address these limitations by transmitting larger datasets and by improving detection robustness through an adaptive threshold. Overall, the results are promising but further work is needed before seismic waves can be considered a viable communication channel for transmission of information between deep geological environments and the surface.
Keywords: Seismic data transmission, subsurface monitoring, Hamming code, signal processing, noise reduction, signal detection, innovative technologies.
How to cite: Akleh, C., Chauris, H., Figliuzzi, B., Fallourd, R., hardouin, P., and Jouve, P.: Robust seismic-wave transmission of digital data in a deep geological environment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18361, https://doi.org/10.5194/egusphere-egu26-18361, 2026.
The safety assessment of a Deep Geologic Repository (DGR) for high-level radioactive waste in Korea necessitates a precise and integrated understanding of subsurface conditions. Building upon previous research that established a basic 3D site model for intuitive geological understanding, this study focuses on developing an integrated 3D visualization tool. The primary objective is to develop the procedures to manage and visualize diverse investigation datasets by integrating them into a coordinate-based 3D framework, thereby enhancing the reliability of site characterization.
The input data for the proposed tool are categorized into geological features and investigation results. Geological features, including volumes and surfaces (e.g., faults), are constructed by interpolating point clouds from surface maps and joining boundaries within the SKUA-GOCAD environment. Investigation data, comprising geotechnical and geophysical results, are structured into a 4x3 matrix based on their spatial forms (point, line, surface, volume) and physical quantities (scalar, vector, tensor). This systematic classification allows the tool to accommodate all standard investigation formats within a unified spatial environment.
The developed visualization tool provides three core capabilities: 1) Spatial Precision: A coordinate-based system ensures the exact locations of multi-source investigation data. 2) Intuitive Visualization of Physical Quantities: The position and magnitude of physical quantities of scalars, vectors, and tensors can be verified intuitively. The tool utilizes RGB color mapping (blue for low values, red for high values) to represent the magnitude of physical quantities, making data interpretation straightforward. 3) Spatial Interaction and Feedback: The tool enables the analysis of geological attributes along borehole trajectories and geophysical cross-sections. This spatial comparison facilitates a feedback loop, allowing the 3D model to be iteratively refined and updated based on empirical investigation data.
Currently, the tool’s functionality has been verified using geological and investigation data from the research testbed. This integrated approach significantly improves the efficiency of site characterization and provides a robust foundation for DGR safety assessments. Future research will focus on program stabilization, thorough verification and the implementation of advanced analytical features to support long-term site monitoring and management.
How to cite: Guk, M., Park, Y., Kim, S.-K., Choi, S.-Y., and Park, J.-H.: Development of a Coordinate-Based 3D Visualization Tool for Integrated Subsurface Characterization of High-Level Radioactive Waste Repositories, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2875, https://doi.org/10.5194/egusphere-egu26-2875, 2026.
Claystone considered as a potential host rock for high‑level radioactive waste disposal in Germany. It offers favorable long‑term safety characteristics—such as low permeability and significant sorption capacity—yet its geomechanical response is governed by low to moderate strength, pronounced anisotropy, and time‑dependent deformation mechanisms including creep, swelling, and moisture‑induced softening. These properties necessitate continuous support throughout the operational lifetime of repository galleries. Due to the unique thermo‑hydro‑mechanical (THM) boundary conditions of a deep geological repository (DGR), standardized support systems from mining and tunneling cannot be directly transferred, particularly at intersections between long‑living and short‑living drifts where stress concentrations and coupled processes are most pronounced.
This study presents a constitutive rock‑behavior‑driven design methodology for concrete support structures at drift intersections in claystone. The numerical framework incorporates elastic–plastic behavior with strain softening and an exponential creep law based on viscoplastic formulations linked to time evolution. A continuum‑mechanical model developed in FLAC3D simulates excavation sequences, support installation, long‑term mechanical evolution of the claystone, and the interaction between the rock mass and elastic liners. The simulations quantify creep‑dominated stress redistribution, deformation localization, the influence of intersection geometry, and the resulting coupling forces acting on the liners. The coupling forces from numerical simulations are transferred to the other programmes like SOFiSTiK and ATENA for feasible deign and nonlinear post-peak analyses untill the collapse of support structure. The resulting conceptual design wokrflow integrates mechanically consistent loading envelopes, reinforcement strategies, and installation procedures tailored to repository‑specific operational and long‑term safety requirements.
The findings demonstrate that accurate representation of anisotropy, softening, and time‑dependent behavior is essential for reliable support design in claystone‑hosted DGRs. The methodology provides a reproducible, physics‑based foundation for designing durable support structures in complex underground intersections.
How to cite: Monnamitheen, A., Simo, E., Herold, P., and Polster, M.: Design of concrete lining for drift intersections in deep geological repository in claystone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20883, https://doi.org/10.5194/egusphere-egu26-20883, 2026.
Natural tracers, such as chloride and the stable isotopes of water, are essential for safety assessments of deep geological repositories for high-level radioactive waste, especially in argillaceous formations. Their concentration profiles in the containment-providing rock zone (CRZ) develop through exchange processes between the host rock and adjacent aquifers. Analyzing these profiles provides insights into the paleohydrogeological evolution of a site and allows conclusions about the dominant transport process over geological timescales. Demonstrating diffusion‐dominated conditions as indicator for the long-term stability of the CRZ is a key safety criterion that can be inferred from pore water chemistry.
Numerical transport simulations are used to reproduce measured tracer profiles. These models usually focus on the geologically recent past, which is constrained by direct measurements of present-day groundwaters. Reconstruction of earlier conditions is associated with higher uncertainties because signals of older hydrogeological changes may have been overprinted. Consequently, the entire paleohydrogeological evolution—from deposition to the most recent changes in the aquifers—is often condensed into an assumption about the initial pore water composition. The highest measured chloride or stable water isotope concentration in the central CRZ is commonly used as a first approximation. Therefore, measured profiles are typically required as input for the simulations.
However, the availability and quality of pore water data are limited during the early phase of a site selection process. In many regions under evaluation in Germany, a data-based analysis of tracer profiles is not feasible. Given these constraints and the safety relevance of these profiles, the question arises how such data gaps can be reduced using available information.
In this study, we examine whether present-day natural tracer profiles of chloride and stable water isotopes can be reproduced through numerical simulations of the paleohydrogeological history of the formations under investigation. We apply this approach to the Swiss siting regions as an example. Here, the shape and maximum values of chloride concentration profiles vary significantly between the boreholes in the siting regions. Key events and characteristic differences in the paleohydrogeology of the regions are identified from independent geological, tectonic, geomorphological, hydrogeological, and hydrogeochemical data, parameterized, and translated into model scenarios. Using numerical transport simulations, we assess (1) whether deviations in chloride and stable water isotope profiles can be attributed to paleohydrogeological factors, (2) to what extent present-day tracer profiles can be approximated with this conceptual approach in an internally consistent logic, and (3) under which circumstances this method can support safety assessments during the site selection process for a deep geological repository for high-level radioactive waste in Germany.
How to cite: Schöne, T. and Hennig, T.: Paleohydrogeological Controls on Natural Tracer Profiles in Northern Switzerland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1001, https://doi.org/10.5194/egusphere-egu26-1001, 2026.
The long-term safety assessment of Deep Geological Repositories (DGR) for high-level radioactive waste has traditionally prioritized the Normal Evolution Scenario (NES). However, guaranteeing robust safety over geological timescales requires accounting for "Dynamic Perturbation Factors (DPFs)"—low-probability, high-consequence events that deviate from expected evolutionary paths. This study identifies 18 key DPFs specific to the geo-environmental context of the Korean peninsula and analyzes their cascading impacts on the repository system using the Korean Features, Events, and Processes (K-FEP) framework.
We defined DPFs as active triggers characterized by abruptness and spatial-temporal uncertainty, capable of exerting multiple impacts on Thermal, Hydraulic, Mechanical, Chemical, and Biological (THMCB) behaviors. Through a systematic classification, we identified 11 natural factors, notably fault reactivation driven by Korea’s high horizontal stress fields and climate change-induced erosion, alongside 7 anthropogenic factors such as future human intrusion (deep drilling).
By mapping these factors to the K-FEP structure, the study elucidates cascading failure mechanisms within the multi-barrier system. For instance, the analysis demonstrates how a seismic event (External Factor) can trigger fault reactivation (Geosphere), potentially shearing canisters and creating new hydraulic pathways for radionuclide migration. The results confirm that DPFs act as critical scenario branching points distinct from the NES. This structured approach provides a scientific basis for developing comprehensive safety cases, refining site selection criteria, and establishing robust design margins against geological uncertainties in Korea.
How to cite: Park, E. S., Chae, B. G., and Oh, S. W.: Dynamic Perturbation Factors in Deep Geological Repository Safety Assessment: Identification and Linkage with the K-FEP Framework, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2296, https://doi.org/10.5194/egusphere-egu26-2296, 2026.
Natural analog studies have long been recognized to support safety cases for the geological disposal of radioactive waste. The uranium ore deposit at the Cigar Lake site in Canada is highly enriched (>55 wt.% U), is located around 450 m below the surface and remained stable since its deposition 1.3 billion years ago. This is related to the presence of a clay‑rich layer, which isolates U and its daughter nuclides from the surface environment. This clay-rich zone mainly consists of illite, a main component of many argillaceous formations considered as suitable host rocks for radioactive waste disposal. Cigar Lake provides a strong and unique natural analog to the multi-barrier system of many disposal concepts.
Iodine, particularly the isotope 129I, is a radionuclide of concern in safety assessments due to its long half-life of 15.7 million years, high mobility, and potential to accumulate in the human body. Naturally, the isotope 129I is produced by neutron‑induced fission of 235U and spontaneous fission of 238U. At Cigar Lake, concentration depth profiles of 129I and U are available over the entire 450 m covering the ore body, clay-rich zone, and surrounding formations. Three zones of U and 129I enrichment were identified. One is located at the depth of the ore body. The other two are at depths of around 270 m and 150 m below the surface. However, measured 129I concentrations do not correspond to the expected theoretical maximum value resulting from the source term calculation for the U isotopes. Compared to the calculated theoretical maximum value, measured 129I concentrations are too low inside (high U concentrations) and too high outside the ore body (low U concentrations). The discrepancy between expected and measured concentrations indicate transport from the ore body through the overburden, via diffusion or through faults. Cigar Lake offers the unique opportunity to investigate 129I migration in an illite‑rich unit on geological spatial and temporal scales giving implications for the near- and far-field of a potential repository.
Quantification of 129I migration processes at Cigar Lake with transport simulations are in the focus of the ANALOG task of DECOVALEX-2027. A step-wise approach is used to identify the underlying processes. First, uncertainties of parameters required for the source term calculation are investigated. This step revealed that the discrepancy between theoretical maximum values and measurements cannot solely be attributed to the source term calculation. Second, migration of 129I from the ore body is therefore modelled with a one‑dimensional diffusion model covering the ore body and the surrounding clay-rich unit. Diffusion and sorption parameters are varied within plausible ranges based on literature values. Results indicate that 129I migration from the ore body must be retarded, either due to very low diffusion or sorption, presumably on minerals other than illite, such as Cu-sulphides. Third, the entire profile of 450 m is modelled including sorption, diffusion, and advection. This integrated approach can help to reduce the uncertainties associated with radionuclide migration and provide a more robust basis for decision-making in the context of radioactive waste disposal.
How to cite: Hennig, T., Zheng, L., and Birkholzer, J. T.: Simulation of iodine migration at Cigar Lake – A natural analog study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2855, https://doi.org/10.5194/egusphere-egu26-2855, 2026.
Safety assessments of deep geological repositories for high-level radioactive waste commonly employ fixed-concentration boundary conditions to represent radionuclide release from the waste form. This approach assumes that the aqueous uranium concentration at the waste-host rock interface equals the thermodynamic solubility of UO2, which is the primary uranium-bearing component in the waste. However, this assumption may overestimate or misrepresent actual uranium release, as it neglects the dynamic interplay between mineral dissolution kinetics and diffusive transport in the surrounding host rock.
In this study, we investigate the coupled processes of UO2 dissolution and uranium diffusion in Opalinus Clay, a clay-rich formation considered as a potential host rock for nuclear waste disposal in Europe. We develop a numerical model using OpenGeoSys (OGS) that explicitly couples a mineral dissolution-precipitation algorithm with diffusive transport. Rather than prescribing a fixed uranium concentration at the source, our approach simulates the dissolution of UO2 as a kinetical or equilibrium-controlled process, allowing the aqueous uranium concentration to evolve dynamically based on local geochemical conditions and transport rates.
Our modeling framework builds upon a dissolution-precipitation algorithm that we have implemented and validated using Python-based equilibrium chemistry solvers. This algorithm is integrated with OGS via a Python-binding library, allowing maximum versatility and enabling reactive transport simulations in realistic geological settings. The primary objective is to quantify the total amount of uranium that can dissolve and diffuse into the host rock over one million years, which is the legal evaluation time required in Germany. We compare our results with those obtained using the conventional fixed-concentration boundary condition to assess whether the commonly adopted simplification leads to conservative or potentially misleading estimates of radionuclide release. Preliminary results and the modeling methodology will be presented, along with a discussion of the implications for repository safety analysis and the potential need for more sophisticated treatment of source-term processes in performance assessments.
How to cite: Shao, H., Jiang, K., Selzer, P., and Lehmann, C.: Investigating solubility-limited uranium release from a high-level waste repository in Opalinus Clay: A numerical modeling approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3963, https://doi.org/10.5194/egusphere-egu26-3963, 2026.
Sorption on mineral surfaces present in (geo-)technical barriers and in host rocks (especially in clay rock and partly in crystalline rock) is a key process constraining the transport of radionuclides from a deep geological nuclear waste repository into the biosphere. The sorption behavior of radionuclides highly depends on the environmental conditions within the deep geological repository system, which may vary spatially and over time. Therefore, a great variety of system parameters involving different sorbing minerals and environmental conditions (e.g. redox condition, ionic strength, pH, presence of complexing ions or microorganisms) need to be considered to assess the mobility of radionuclides.
This study provides a high-level overview of which systems (i.e. combinations of radionuclides, minerals and environmental conditions) have already been investigated extensively and which systems have been addressed in only few studies or not at all. The developed systematic evaluation of the state of knowledge concerning the sorption of iodine, neptunium and technetium (as representatives for safety-relevant elements) in different oxidation states includes a literature survey and a categorization of the references in a literature database with regard to the studied systems. The overarching goal of this evaluation is to identify persisting knowledge gaps and to assess the relevance for the ongoing site selection procedure in Germany and the long-term safety assessment of deep geological nuclear waste repositories in general.
Preliminary results show that iodine, neptunium and technetium sorption has already been extensively studied at neutral and slightly alkaline conditions and at low to moderate ionic strengths. Also, the influence of carbonate and divalent cations (mainly Ca) has received significant attention. However, some environmental conditions constitute knowledge gaps in sorption studies for all three examined elements and all considered solids. These are for example: high ionic strength (> 1 M), high temperatures (> 25°C) and the influence of organic ligands and microorganisms. The outcome of the project will be a sorption literature database with the possibility to search and filter references for the assigned categories.
How to cite: Philipp, T., Weyand, T., and Bracke, G.: Identification of knowledge gaps regarding iodine, neptunium and technetium sorption in the context of deep geological nuclear waste disposal, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5127, https://doi.org/10.5194/egusphere-egu26-5127, 2026.
Radioactive storage is becoming a critical component of industrial waste management. Thorium and Uranium are the primary waste of nuclear power plants and increasingly present in waste from other sectors. While bentonite is often suggested as the primary backfill in repositories, zeolites (e.g. clinoptilolite) are frequently proposed and used as specialized reactive fillers and barrier materials within storage containers and concrete matrices.
In this research we test a novel reactive barrier material for immobilization of Th via coprecipitation with low-solubility lead phosphates (pyromorphite, Pb5(PO4)Cl). The material consists of a mixture of Pb-modified zeolite clinoptiloite and hydroxylapatite. Appropriate methodology of zeolite activation allows us to obtain a Pb-modified clinoptilolite which is safe for the environment (no Pb release in water) but still is reactive enough that in contaminated waters it acts as a Pb source for the precipitation of Pb phosphates [1]. In this system, hydroxylapatite acts as a source of PO43- anions and as a source of Ca ions which can replace Pb on the surface of zeolite through ion exchange. Upon contact with a solution containing radioactive contaminants and Cl, a reaction is expected to produce pyromorphite with incorporated Th as the dominant phase.
To test this model an experiment was conducted in which a mixture of Pb-modified zeolite and hydroxylapatite reacted with solutions containing Th and Cl in pH = 5. Analyses of both the solutions and solid phases were carried out to ascertain the efficiency and mechanisms of the processes.
The reaction with a mixture of Pb-zeolite and hydroxylapatite results in formation of Th-bearing pyromorphite. Powder X-ray diffraction and SEM analyses of the precipitates has shown that a reaction has occurred in all the experiments, with pyromorphite crystals up to 2 μm formed on the surfaces of both zeolite and hydroxylapatite. The reaction is very effective, with Th concentrations lowering from 5 ppm to less than 10 ppb. Precipitation of pyromorphite in the presence of Th (1g/L) results in complete removal of Th from the solution (control experiment).
The proposed mechanism is coprecipitation of Th with Pb-phosphates, principally pyromorphite (potentially accompanied with Th sorption on zeolite). The coprecipitation of Th with pyromorphite occurs according to the following reaction:
Pb-zeolite + Ca5(PO4)3OH + Th4+ + Cl- => (Pb,Th)5(PO4)3Cl ↓ + Ca-zeolite
It is likely that minor amounts of other Pb phosphates precipitate together with pyromorphite and may contribute to the removal of Th from solution. This will be addressed in future studies. The method described might lead to a new technology that allows for selective, permanent and effective way to remove radioactive elements. A mixture of Pb-modified clinoptilolite and hydroxylapatite may serve as a reactive barrier and as a supplementary backfill material in storage containers and underground repositories for radioactive waste. This research was partly funded by NCN research grant no. 2024/55/B/ST10/01958.
[1] Stępień, E., Manecki, M., Bajda, T. 2025. Mimetite precipitation on Pb-clinoptilolite: an effective approach for arsenate removal from water. Mineralogia, vol. 56, 44-51. DOI: 10.2478/mipo-2025-0006
How to cite: Leś, M. and Manecki, M.: A novel approach to Th immobilization via coprecipitation with Pb-apatite on a mixture of Pb-modified clinoptilolite and hydroxylapatite , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18940, https://doi.org/10.5194/egusphere-egu26-18940, 2026.
Evaluating the long-term behaviour of the engineered barrier system (EBS) in a deep geological repository for high-level radioactive waste (HLW) relies on the application of advanced reactive transport models with a high level of physical and chemical detail. In this context, the EBS comprises the waste canister, the compacted bentonite buffer, and the surrounding concrete liner. In parallel, artificial intelligence and machine learning (ML) techniques are advancing rapidly and are increasingly applied to: (a) speed up numerical computations, (b) handle complex multiscale and multiphysics interactions, and (c) support uncertainty quantification and sensitivity analysis. In this work, we develop metamodels aimed at representing steel canister corrosion processes, the formation of corrosion products, and their interactions with compacted bentonite. These metamodels act as efficient surrogate representations of high-fidelity reactive transport simulations, providing accurate approximations while substantially reducing computational cost.
A metamodel has been developed for a geochemical system with interactions of steel/bentonite and precipitation of corrosion products. The system includes 3 primary dissolved species (Fe2+, H+ and O2aq), 4 aqueous complexes and two minerals (magnetite and goethite). A set of 500.000 data were sampled with a Latin Hyper Cube (LHC) sequence. Batch simulations were performed with CORE2Dv5 with 3 inputs corresponding to the total concentrations of Fe, H and O2. Outputs include primary and secondary dissolved species, total dissolved and total precipitated concentrations, magnetite, goethite, pH and Eh. The hybrid metamodel is based on Random Forests for group identification and Gaussian Processes for output predicition. A total of 7 groups were defined based on the presence or absence of minerals and some preselected ranges of Eh and pH (pH ≤ 9 and pH > 9). The metamodel provides excellent results for most of the output variables. Working with log-concentrations improves significantly results for some dissolved and precipitated concentrations. When the metamodel is trained by working with concentrations of dissolved Fe, the validation results show some negative concentrations. On the other hand, when the metamodel is trained by working with the logarithm of the concentrations of dissolved Fe, the predicted validation concentrations are always positive, but the metrics of the validation are slightly worse. The accuracy of the metamodel improves significantly by defining 7 groups with Random Forests. The metamodel shows excellent results for predicting mineral and total precipitated concentrations. The CPU for training the Gaussian process increases significantly with the number of training samples. Work is in progress to implement the metamodel into CORE2Dv5 for testing the improvements in CPU time provided by the metamodel.
Acknowledgements: The research leading to these results was funded by ENRESA through Research Contracts within the Work Package ACED of EURAD (European Joint Programme on Radioactive Waste Management of the European Union), HERMES Work Package of EURAD 2 (Grant Agreement No. 101166718), the Spanish Ministry of Science and Innovation Project HERCULES (PID2023-153202OB-I00) and the Galician Regional Government (Grant Number ED431C 2025/55).
How to cite: Samper, J., Mon, A., Sobral, B., and Montenegro, L.: Metamodels of Chemical System Solvers for Reactive Solute Transport in Engineered Barrier–Steel Canister Interactions in HLW Repositories, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21520, https://doi.org/10.5194/egusphere-egu26-21520, 2026.
Since radioactive waste remains hazardous far beyond conventional planning horizons, climate change is treated as a fundamental external driver that can alter geological, hydrological, geochemical, mechanical, and biospheric processes relevant to containment and isolation over very long time periods, ranging from one hundred years to one million years. This presentation addresses knowledge gaps, constraints and recommendations regarding long-term influence of climate evolution on the safety of radioactive waste disposal systems in Europe, as collected during the EURAD-2 strategic study CLIMATE.
A regional framework is applied in this study, distinguishing various climate zones, each with characteristic future climate trajectories and dominant safety-relevant processes. Across disposal concepts (surface disposal systems, near-surface or shallow geological facilities, and deep geological repositories), disposal phase (construction, operational, post-closure period) and climate zones in Europe (oceanic-subtropical-continental), this work examines how prolonged warming, renewed glaciations, permafrost development, sea-level change, erosion, and extreme hydroclimatic events are taken into account in climate-impact assessments. It highlights the uneven maturity of current methodologies, the strong dependence of long-term projections on assumptions about future greenhouse gas emissions, and the persistent limitations in regional downscaling and process coupling.
By identifying common patterns, regional differences, and critical knowledge gaps, the strategic study CLIMATE establishes a coherent basis for improving climate-informed safety assessments and for prioritizing future research needed to support robust, defensible long-term disposal strategies.
How to cite: Beerten, K., Park, J., Geisler-Roblin, A., Petie, L., Vercelli, M., and Sainz Garcia, A.: EURAD-2 Work Package CLIMATE: Impact of climate change on nuclear waste management , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21761, https://doi.org/10.5194/egusphere-egu26-21761, 2026.
