Session T5f

T5f | Challenges and innovations in permeability assessment: from lab to digital twins of geological systems

Challenges and innovations in permeability assessment: from lab to digital twins of geological systems

Main Session Organizers: Ben Laurich, Joyce Schmatz, Richard Jayne, Carlo Dietl

Orals

| Wed, 17 Sep, 10:50–12:30 (CEST)|Room Studio 2

Posters

| Attendance Wed, 17 Sep, 14:40–15:40 (CEST)|Poster area

This session is aimed towards different aspects of permeability, including its laboratory and in situ measurement and its critical upscaling required for modeling geological systems. We welcome keen laboratory and in-situ researchers as well as numerical modelers to discuss the challenges in and relevance of permeability assessment, regardless of the type of host rock or barrier material.

Key Laboratory Topics:
• Challenges in Measuring Low Permeability: Explore the pitfalls of measuring the lowest permeability values and how to overcome them.
• Unverified Method Comparability and Round-Robin Tests: Discuss the variability across measurement techniques and how collaborative round-robin testing can pave the way for greater comparability.
• Standardization Procedures for Site Selection: Debate the feasibility of developing standard procedures for permeability measurements, which are crucial for reliable evaluation and eventual site selection.
In Situ Measurement Topics:
• Distinguishing Flow Processes Across Scales: How to measure, distinguish and map fracture and matrix flow?
• Spatial and Volumetric Extrapolation: Discuss how to extrapolate localized permeability measurements to larger, reservoir or disposal-site scales, ensuring representativeness and reliability in assessments.
Numerical Modeling Topics:
• Upscaling Micro-Scale Processes: Delve into how small-scale measurements can be scaled to accurately represent larger geological systems.
• Fracture Networks to Equivalent Porous Media: Examine methods to modify discrete fracture networks into equivalent porous media to support the development of large-scale, realistic digital twins of geological systems.
• Future developments of barriers and geosphere: How to deal with changes of porosity due to mechanical load or precipitation of secondary phases, how (un)certain is pore-clogging?

The session will also provide room to discuss two-phase flow, relative permeability and the material dependency of environmental controls, which might dynamically change throughout the long-term evolution of a repository.

Orals: Wed, 17 Sep, 10:50–12:30 | Room Studio 2

10:50–11:10

safeND2025-155

Twenty years of claystone transport research: Methods, challenges and lessons learned

Garri Gaus

Claystones are important in a wide range of geological applications, functioning both as effective caprocks for subsurface fluid storage and as potential host formations for radioactive waste disposal. For over 20 years, the Petrophysics Group - led by Dr. Bernhard Krooss and Prof. Dr. Ralf Littke at the Institute of Geology and Geochemistry of Petroleum and Coal, RWTH Aachen University - has investigated different flow regimes, including advection, slip flow and diffusion, using various fluids such as water, hydrogen, methane and carbon dioxide. The primary focus has been the precise characterization of transport properties under varying boundary conditions, including temperature, lithostatic and pore pressures, fluid composition and degree of water saturation. To achieve this, the group has applied many different measurement techniques, ranging from steady-state methods to nonsteady-state pulse-decay tests, classic and “unconventional”, such as radial and axial uptake techniques. In this contribution, we discuss the sensitivities and potential pitfalls encountered when using these methods, illustrating our findings with representative datasets collected over the past 20 years. We also present recent findings from the ongoing MATURITY project (co-funded by the Federal Ministry of Education and Research and the Federal Company for Radioactive Waste Disposal), in which we systematically compare laboratory-based permeability coefficients, obtained through various measurement techniques, with field-scale observations to identify potential discrepancies and evaluate their implications. In addition, we examine how different core storage conditions affect transport properties by analyzing samples from the same locations, where one set has been stored under ambient conditions since the 1980s, and another set was vacuum-sealed in aluminum-laminate foil immediately after retrieval. Finally, we emphasize the need for establishing standardized testing protocols and adopting benchmark samples to ensure both reproducibility and comparability of permeability data across different laboratories and research teams, complementing the discussion with our own datasets. This overview underscores the importance of robust experimental design and careful data interpretation in advancing our understanding of claystone transport properties.

How to cite: Gaus, G.: Twenty years of claystone transport research: Methods, challenges and lessons learned, Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-155, https://doi.org/10.5194/safend2025-155, 2025.

11:10–11:30

safeND2025-167

From outcrops and laboratory rock samples to three-dimensional fracture and flow pathway modelling

Nikolas Ovaskainen

Discontinuities, i.e. fractures, form the dominant pathways for fluid flow within crystalline bedrock. Characterizing these fracture networks involves integrating data across multiple scales. Field observations from outcrops yield macroscopic structural data, often analysed in two dimensions for geometric and topological properties using tools like fractopo (Ovaskainen 2023). Complementary three-dimensional data comes from oriented drillcores, while X-ray computed tomography (CT) imaging of laboratory rock samples provides crucial microscale details of fracture geometry and rock matrix properties. To understand fluid behaviour at larger scales relevant to practical applications, discrete fracture network (DFN) modelling is often necessary. However, constructing and simulating flow within these three-dimensional fracture models presents challenges. The required software can be complex, often proprietary, while free and open-source alternatives may lack user-friendliness or sustained development.

Predicting fluid flow pathways accurately through fractured rock is essential for the safety of, e.g., geological disposal of nuclear waste, geothermal energy extraction and management of groundwater resources. A gap exists between the multi-scale field, laboratory and digitized datasets geologists can collect and the use of these observations in three-dimensional fracture and flow pathway modelling. Solutions exist, especially as proprietary software but those lack transparency due to the closed-source nature. Bridging this gap is crucial for improving the reliability of subsurface flow predictions. Furthermore, more effort is required to effectively translate the detailed data a geologist captures, encompassing field observations, digitized outcrop fracture traces, and laboratory rock sample scans, into comprehensive, upscaled, three-dimensional fracture network models, for instance, through the use of DFN-modelling.

This research focuses on coupling field observations with laboratory rock sample CT-scans and flow experiments. We have characterized fracture networks at the macroscale from outcrops using established 2D analysis techniques (E.g., Ovaskainen et al. 2023). Concurrently, we have analysed microscale fracture characteristics and rock properties from laboratory rock samples using X-ray CT imaging. Our current work involves integrating these distinct datasets, which capture both field-scale distributions and lab-scale details, into preliminary three-dimensional fracture network models and flow simulations using free and open-source tools, such as MPLBM-UT (Santos et al. 2022). The emphasis has firstly been on trying to inform model construction through a geological lens, rather than focusing solely on mathematical or computational abstractions and, secondly, to use free and open-source software for this purpose to attempt to bridge the gap between the field, lab and models for a more wider field of experts.

Ovaskainen, Nikolas. 2023. “Fractopo: A Python Package for Fracture Network Analysis.” Journal of Open Source Software 8 (85): 5300. https://doi.org/10.21105/joss.05300.

Ovaskainen, Nikolas Aleksi, Pietari Mikael Skyttä, Nicklas Johan Nordbäck, and Jon Oskar Engström. 2023. “Detailed Investigation of Multi-Scale Fracture Networks in Glacially Abraded Crystalline Bedrock at Åland Islands, Finland.” Solid Earth 14 (6): 603–24. https://doi.org/10.5194/se-14-603-2023.

Santos, Javier E., Alex Gigliotti, Abhishek Bihani, Christopher Landry, Marc A. Hesse, Michael J. Pyrcz, and Maša Prodanović. 2022. “MPLBM-UT: Multiphase LBM Library for Permeable Media Analysis.” SoftwareX 18 (June): 101097. https://doi.org/10.1016/j.softx.2022.101097.

How to cite: Ovaskainen, N.: From outcrops and laboratory rock samples to three-dimensional fracture and flow pathway modelling, Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-167, https://doi.org/10.5194/safend2025-167, 2025.

11:30–11:50

safeND2025-130

Determining the physics of gas migration in Opalinus Clay; The Gas Transport (GT) project

Robert Cuss, Jocelyn Gisiger, Antonio Rinaldi, Manuel Sentis, Frederic Bernier, Fabien Magri, David Jaeggi, and Jon Harrington

Gas is produced in a deep geological repository mainly by metal corrosion of the waste and repository infrastructure. Since the Opalinus Clay (OPA) is a dense clay-rich host rock and the gas cannot be easily transported away, gas formation causes an increase in pressure that can affect the safety barriers. According to the current state of knowledge, there are four basic gas transport mechanisms in claystone: (i) gas movement by solution and/or diffusion; (ii) gas flow in the original porosity of the fabric, referred to as visco-capillary (or 2-phase) flow; (iii) gas flow along localised dilatant pathways; and (iv) gas flow along macro fractures similar in form to those observed in hydrofracture activities. The diffusion of gases through clay-rich rocks is relatively well understood and can be modelled to predict how the repository system will behave after closure. Considerable effort in recent years has been placed on understanding the advective transport of gas, which can occur if diffusion through the host rock is insufficient to keep the gas pressure low. The primary aim of the GT experiment was to gain definitive evidence of whether mechanism (ii) or (iii) are the dominant advective gas transport mechanisms in OPA.

The GT experiment employed a complementary three-tier approach with (1) a series of closely constrained laboratory experiments helping to define (2) a field experiment at the Mont Terri underground research laboratory in Switzerland. (3) This were supplemented by modelling the experimental data. Both experimental programs were designed to observe the coupling of stress, strain, and pore pressure during gas movement.

Four laboratory experiments were conducted: two with the long axis of the test sample parallel with bedding and two perpendicular. The samples dilated as gas started to move, with gas flow favouring pre-existing bedding planes.

The field experiment was constructed at Mont Terri in November 2020 with a central injection borehole with three injection intervals surrounded by eight monitoring boreholes. All 8 monitoring boreholes had fibre optic cabling, with two boreholes having extensometers, one having extensometers/inclinometers, and one monitoring pore pressure. After a period of stabilisation and hydraulic testing, a gas injection test was initiated in September 2022. Coupling was seen between pore pressure, strain (extensometers & inclinometers; and fibre optics), and gas injection pressure at gas entry. Close examination of the response shows that gas movement was directional and not evenly distributed around the injection borehole.

Confidence in experimental data is increased by modelling the data. This is being achieved through a PhD study and by modelling teams in the DECOVALEX-2027 HyMAR task. Similar experiments have been used previously in DECOVALEX and found to fail to represent all features seen in the data when using 2-phase flow codes. In HyMAR, the teams are modelling the experiments considering concepts such as damage to better represent the response seen in the data. Therefore, uncertainty in our understanding of the physics of gas migration in OPA has been tackled using a combination of laboratory, field, and modelling approaches.

How to cite: Cuss, R., Gisiger, J., Rinaldi, A., Sentis, M., Bernier, F., Magri, F., Jaeggi, D., and Harrington, J.: Determining the physics of gas migration in Opalinus Clay; The Gas Transport (GT) project , Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-130, https://doi.org/10.5194/safend2025-130, 2025.

11:50–12:10

safeND2025-97

Hydro-Mechanical Analysis of Packer Test in Opalinus Clay: Implications for Formation Pressure Estimation

José Bosch, Eleonora Crisci, Silvio Giger, and Aldo Madaschi

Opalinus Clay is a shale formation that has been chosen as a host rock for the construction of a radioactive waste repository in Switzerland. This work presents an advanced hydro-mechanical (HM) analysis of a hydraulic packer test conducted in the Opalinus Clay shale section of a deep borehole drilled for repository site characterization. The analysis aims to enhance the interpretation of packer test results by evaluating the effects of mechanical processes on hydraulic conductivity and formation pressure estimation, which are crucial for assessing the long-term safety of potential nuclear waste repositories.

The approach involves developing a unified 3D HM coupled model using finite elements that integrates all stages of the packer test, accounting for vertical anisotropy in permeability and mechanical properties. The study incorporated two stages: (i) Poroelastic modelling and (ii) Elastoplastic analysis.

First, the Opalinus Clay is modelled as a linear-elastic anisotropic material. The model considers the stress release due to borehole opening, the total stress applied by the drilling mud, and the pore pressure increment resulting from the drilling fluid pressure. A parametric analysis is performed, focusing on hydraulic parameters, varying horizontal hydraulic conductivity and formation pressure to evaluate their impact on test results.

For the second stage, the elastoplastic model eADP (Madaschi et al. 2023) is used to evaluate the effects of non-linear stress-strain behaviour and the formation of damage zones on test outcomes. The model incorporates elasto-plastic anisotropy and reproduces the quasi-brittle behaviour that characterizes shales. The constitutive parameters have been calibrated with an extensive dataset of laboratory mechanical tests on Opalinus Clay sourced from the sites under investigation by Nagra (Crisci et al. 2024).

The results indicate that while the interpreted value of permeability using pure hydraulic models can be considered robust, the formation pressure is affected by mechanical perturbations. The elastoplastic analysis reveals that the development of a damage zone around the borehole can significantly influence the pressure build-up during the test. The modelling results assist in quantifying the effects of borehole disturbance on the hydraulic head derived from packer tests and allow to better reconcile those with results from long-term monitoring data.

References:

Crisci, E., Giger, S.B., Laloui, L., Ferrari, A., Ewy, R., Stankovic, R., Stenebråten, J., Halvorsen, K., Soldal, M., 2024. Insights from an extensive triaxial testing campaign on a shale for comparative site characterization of a deep geological repository. Geomechanics for Energy and the Environment 38, 100508. https://doi.org/10.1016/j.gete.2023.100508.

Madaschi, A., J., Leuthold, L., Cantieni, L., Laloui (2023). Comparative numerical calculations in the context of tunnel design for nuclear waste repositories in Opalinus Clay. Proceedings 10th European Conference on Numerical Methods in Geotechnical Engineering. London. Zdravković L, Konte S, Taborda DMG, Tsiampousi A (eds).

How to cite: Bosch, J., Crisci, E., Giger, S., and Madaschi, A.: Hydro-Mechanical Analysis of Packer Test in Opalinus Clay: Implications for Formation Pressure Estimation, Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-97, https://doi.org/10.5194/safend2025-97, 2025.

12:10–12:30

safeND2025-164

Developing reference methods for measuring ultra-low permeability in Mercia mudrocks: implications for safe subsurface nuclear waste disposal

Zaid Jangda, Nathaniel Forbes Inskip, Andreas Busch, and Niko Kampman

Safe and timely disposal of high-level nuclear waste is an urgent global priority due to risks associated with prolonged above-ground storage, including geopolitical instability, environmental hazards, and potential contamination. Geological Disposal Facilities (GDFs), which isolate radioactive waste deep underground within stable geological formations, are internationally recognised as the most effective solution. These facilities rely on a multi-barrier approach, combining engineered vaults with natural geological barriers to ensure long-term containment and isolation.

In the UK, current site evaluations for a GDF have provisionally identified the Triassic Mercia Mudstone Group (MMG) as a suitable geological barrier. The MMG is considered attractive due to its widespread availability, low permeability, proven effectiveness as hydrocarbon seals, and favourable mechanical properties. However, to fully assess its suitability, it is important to consider the geological complexity. The MMG exhibits significant heterogeneity, with marked vertical and lateral changes in sedimentary facies and lithological composition over short distances. In addition, its diagenetic history, involving burial at depths exceeding those targeted for geological disposal, has resulted in over-compaction and relatively stiff and brittle rock properties. These characteristics may influence fracture behaviour and permeability and therefore warrant detailed characterisation during site assessments.

Reliable permeability measurement in these ultra-low permeability mudrocks is challenging yet crucial, as even minor leakage could have severe environmental consequences. This research addresses this critical knowledge gap by developing robust, reproducible laboratory methods specifically tailored to measure permeability in MMG samples obtained from the Gateway 1e borehole. Using highly saline fluids representative of realistic repository conditions, we systematically measure permeability under subsurface pressure conditions and varying ionic strengths, closely simulating in situ geological environments.

This approach addresses key methodological gaps in permeability assessment, particularly concerning fluid-rock interactions under realistic salinities. Such targeted experimentation, rarely conducted before, will produce essential reference data and novel empirical correlations, facilitating accurate permeability upscaling and improved numerical modelling for site assessments. By enhancing the accuracy and reliability of permeability measurements in the complex geological context of the MMG, our findings will provide crucial scientific evidence for the UK’s ongoing GDF siting process. This will support informed decisions about geological suitability, engineering feasibility, and long-term safety, while also offering valuable insights and reference methods applicable to similar geological disposal programmes worldwide.

How to cite: Jangda, Z., Inskip, N. F., Busch, A., and Kampman, N.: Developing reference methods for measuring ultra-low permeability in Mercia mudrocks: implications for safe subsurface nuclear waste disposal , Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-164, https://doi.org/10.5194/safend2025-164, 2025.

Posters: Wed, 17 Sep, 14:40–15:40 | Poster area

P24

safeND2025-91

Two-phase flow characterization and modelling in bentonite at various temperatures

Eleonora Crisci, José Bosch, Raphael Schneeberger, Alexandros Papafotiou, and Florian Kober

Bentonite is considered a key buffer material for deep geological repositories. During repository evolution, water and vapour redistribution around the canisters governs several processes affecting the sealing properties of bentonite, such as swelling and density homogenisation. A thorough characterization of the material's thermal and hydraulic properties is essential for numerical model calibration and predicting the response of the Engineered Barrier System. In this work, we present an experimental campaign investigating the thermo-hydraulic response of bentonite in partially saturated conditions at two temperature levels, complemented by numerical THM modeling to analyse the contributions of vapour and liquid to the overall transport.

Water retention curves were obtained at 20°C and 50°C on free-swelling samples. At high suctions, water content is independent of void ratio since most water is expected to be in an adsorbed form, whereas at low suctions, results vary between constant volume and free swelling samples due to the influence of capillarity and the diffuse double layer. Results were compared with previous studies at room temperature and interpreted using the Van Genuchten equation. The retention curve was also compared with the model proposed by Bosch et al. (2023), which explicitly considers adsorbed and free water fractions.

Hydraulic conductivity was determined over a wide saturation range at 20°C and 50°C using the instantaneous profile method on two 25 cm-long cylindrical bentonite samples, initially at a homogeneous degree of saturation and compacted to a target dry density of 1.55 g/cm³. The samples were hydrated from one side with artificial pore water, to replicate in-situ brine composition. Upon contact with the brine, relative humidity (total suction) was periodically measured at five positions along the sample height to assess saturation evolution. These measurements, combined with the water retention curve, enabled the calculation of pressure gradients and water flux, allowing for the determination of hydraulic conductivity.

The adopted methodology enabled the evaluation of hydraulic conductivity evolution as a function of suction and degree of saturation, providing relative permeability curves and allowing for the calibration of appropriate models. The results also assess the impact of temperature on hydraulic conductivity. At laboratory temperature, hydraulic conductivity increased with saturation, spanning two orders of magnitude from 1×10⁻¹³ m/s (high saturation) to 1×10⁻¹⁵ m/s (low saturation). Higher water fluxes were recorded at 50°C, highlighting the role of temperature in enhancing water transport.

The collected data provide insight into how temperature influences overall fluid transport through its effects on vapor transport and water viscosity. These findings allowed the calibration of a THM numerical model to analyse the relative contributions of liquid and vapour transport mechanisms in bentonite, improving the predictive capability of engineered barrier system performance.

References

A. Bosch, A. Ferrari, O. Leupin, and L. Laloui, “Modelling the density homogenisation of a block and granular bentonite buffer upon non-isothermal saturation,” Int. J. Numer. Anal. Methods Geomech., vol. 47, no. 11, 2023, doi: 10.1002/nag.3547.

How to cite: Crisci, E., Bosch, J., Schneeberger, R., Papafotiou, A., and Kober, F.: Two-phase flow characterization and modelling in bentonite at various temperatures, Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-91, https://doi.org/10.5194/safend2025-91, 2025.

P25

safeND2025-96

Low Perm – Development of a calibration standard for evaluating permeability measurements of tight rocks

Carlo Dietl, Dirk Prinz, Marcus Emmel, Ben Laurich, Antoine Fourrière, and Simon Weides

Permeability of tight rocks is an important subject where fluid-rock interaction is concerned. It is of particular importance in the site selection process for a deep geological repository for high-level radioactive waste. According to the German site selection act the containment-providing rock zone shall isolate the waste and prevent or limit transport of radionuclides from the repository into the biosphere for 1 Ma. Consequently, the permeability of the host rock needs to be very low.

However, permeability measurements of tight rocks are a great challenge for rock physics laboratories. There is a wide variety of measurement methods and analytical equipment. Therefore, the data from different laboratories are generally hard to compare and it is difficult to build a trustworthy, comprehensive and reproducible permeability data base for possible host rocks of a disposal site for nuclear waste. This is of particular importance because trust in the applied data base is one key factor for a successful site selection process. Against this background it is desirable to:

develop a calibration standard with uniform and consistent rock physical properties
test this standard at various laboratories which apply different permeability testing methods and experimental setups.

Such a round robin test with a well-defined, homogeneous and stable standard would allow a reliable comparison of measurement results of the applied methods and support comparability of permeability measurements of tight materials.

The research project Low Perm, which we present here, is geared towards both these objectives and aims to improve the objective comparability of measured permeability values of tight rocks.

In a first step a calibration standard on corundum (Al₂O₃) basis is currently developed. Corundum is chemically resistant, has high mechanical strength, high temperature stability and low thermal expansion. The aim is to produce a ceramic with a porosity of roughly 30 % with pore diameters averaging between 10 and 100 nm and – most importantly – a permeability of 10^-18 to 10^-20 m². For this purpose, the Al₂O₃ granulate was first uniaxially formed into a cylindrical shape and then isostatically compacted at pressures between 100 and 300 MPa. Finally, the samples were sintered at temperatures between 1300° and 1600°C.

Quality control of the test specimens, i.e. determination of porosity and permeability, is done by a combination of He pycnometry, sorption measurements as well as BIB-SEM imaging, radial diffusion and gas permeability measurements. So far, specimens sintered at 1350°C and 300 MPa are closest to the desired permeability with 9.438 x 10^-18 m² (at a porosity of 38 %). A specimen at 1400°C / 300 MPa is currently investigated. It is expected that the permeability of this specimen is close to 10^-19 m², which in turn should make it a suitable calibration standard.

The developed specimens will be sent to five laboratories (yet to determine) for a round robin test. Each of them will carry out permeability measurements of five samples. Each laboratory will apply its own permeability testing methodology and equipment. This will be done to evaluate the permeability testing concepts of the participants. The results of the benchmark will eventually be discussed jointly, evaluated and published under open access.

How to cite: Dietl, C., Prinz, D., Emmel, M., Laurich, B., Fourrière, A., and Weides, S.: Low Perm – Development of a calibration standard for evaluating permeability measurements of tight rocks, Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-96, https://doi.org/10.5194/safend2025-96, 2025.

P26

safeND2025-112

KAFKA: Compartment model for flow dynamics and solute transport in a converging underground waste repository (Kompartimentmodell für die Ausbreitung und die Fluiddynamik in einer konvergierenden Untertageanlage für Abfälle)

Laurin Wissmeier, Gerhard Mayer, and Sebastian Röthlin

KAFKA (Kompartimentmodell für die Ausbreitung und die Fluiddynamik in einer konvergierenden Untertageanlage für Abfälle, compartment model for flow dynamics and solute transport in a converging underground waste repository) is a numerical software package for simulating flow and transport processes in underground salt rock repositories for radioactive waste disposal.

The latest version, KAFKA3, was developed by CSD Engineers AG, Aarau, Switzerland, for the Federal Company for Radioactive Waste Disposal (BGE), Germany, based on in its previous version, KAFKA2. It uses a site-specific structural model representing repository conditions through simplified compartments and solves flow and transport equations using the finite-volume method.

KAFKA accounts for effects such as two-phase gas/liquid flow, density-driven flow, repository flooding, salt rock convergence, mineral transformation, solute transport with sorption, solubility, radioactive decay, as well as gas generation.

Key updates in KAFKA3 include a revised numerical approach, an alternative gas generation model considering water availability, a generalized re-dissolution process for mineral reactions and the consideration of capillary effects. These enhancements improve flexibility for assessing closure measures, emergency scenarios, and long-term safety through deterministic or probabilistic calculations.

In our presentation we detail the design principles, discuss the numerical approach, show verification examples and demonstrate a generic application in combination with probabilistic uncertainty and sensitivity analyses.

How to cite: Wissmeier, L., Mayer, G., and Röthlin, S.: KAFKA: Compartment model for flow dynamics and solute transport in a converging underground waste repository (Kompartimentmodell für die Ausbreitung und die Fluiddynamik in einer konvergierenden Untertageanlage für Abfälle), Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-112, https://doi.org/10.5194/safend2025-112, 2025.