DFN Modelling Workshop for Nuclear Waste Repositories – 9th – 12th of June 2026

9 Jun 2026, 10:00 → 12 Jun 2026, 16:00 Europe/Stockholm

2003 Lärosal (Sweden, Uppsala Universitet, Ångströmlaboratoriet)

Jon Engström (Geological Survey of Finland), Nikolas Ovaskainen (Geological Survey of Finland), Sarah Weihmann (RWTH Aachen University)

We are pleased to invite you to participate in our second

DFN Modelling Workshop for Nuclear Waste Repositories - Stuck Between a Rock and a Hard Place?

The workshop is hosted by The Chair of Repository Safety (ELS) and Geological Survey of Finland (GTK) from 9th – 12th of June 2026 in Uppsala, Sweden at Ångströmslaboratoriet. While the main workshop will be held 9th to 11th of June, an excursion to Forsmark, the Swedish deep geological repository site in crystalline fractured rock, is scheduled for 12th of June. The excursion is optional and, like the workshop, free of cost. However, spaces for the excursion are limited, so please sign up early to secure your spot.

Objectives

The workshop brings together experts in discrete fracture network (DFN) modelling to explore and discuss free and open-source software solutions for nuclear waste repositories in fractured rock. The software to be demonstrated will include OpenGeoSys and porepy, and the number of software will continue to be updated here as registration starts. The objectives are to:

• Showcase and critically evaluate existing open-source software tools through presentations and hands-on demos/hackathons
• Foster exchange and collaboration on DFN-modelling approaches and challenges across geological settings
• Develop recommendations for modelling approaches in nuclear waste disposal

Preliminary structure

• Day One: Expert presentations from participants addressing current challenges and advancements in DFN modelling (10:00 - 17:00)
• Day Two: Hands-on demos/hackathon sessions of free and open-source software to learn about functionalities and possible use cases (10:00 - 17:00)
• Day Three: Presentations and demos alongside gathering of collective recommendations for future research collaboration and modelling considerations for nuclear waste disposal (10:00 - 13:00)
• Day Four: Optional excursion to Forsmark (08:00 - 16:00)

Logistics & Costs

• Participants are expected to cover their own travel and accommodation costs. 
• We strongly encourage participants to bring their own laptops to both present their own software/projects and test software discussed during the workshop.
• See https://www.uu.se/en/campus/angstrom-laboratory/visit-us for information about the venue.
• All presentations and demonstrations are held in Lärosal 2003
  • See campus map for exact location: Link
  • You can most easily enter Ångströmslaboratoriet at Hus 10, then see the campus map, follow the signs or ask the reception for guidance

Platform notes

Before the workshop, if you have submitted a presentation contribution, we would prefer if you uploaded presentation materials through the platform by creating an account at indico.global. Please note the "Protected" field. It determines if you presentation is publicly available to everyone, only for participants or only for the organizers. Guideline to only show for participants: Toggle on "Protected", then click "Registrants" and choose the "Registrations for ..." option.

For those holding demos/hackathons, we will contact you separately regarding how materials will be distributed to participants.

This site will continue to be actively updated until and after the workshop so please stay tuned. The timetable of presentations and demos along with their titles and abstracts will be published at the latest shortly after the call for contributions/abstracts has ended mid April.

Please do not hesitate to contact us about the workshop, any issues or about this platform! See contact emails on the left.

Technical requirements

To follow along with software demonstrations using your own devices, you might need to register accounts at cloud services and/or install software to your computers. Please follow this link to reach the top repository with all technical requirements listed:

https://github.com/nialov/dfn-modelling-workshop-for-nuclear-waste-repositories-2026

The linked repository will itself contain links to the specific instructions for the demonstrated software.

Top repository for instructions related to workshop demonstrations

Tuesday 9 June

10:00 → 13:00 Presentations: Morning

Convener: Nikolas Ovaskainen (Geological Survey of Finland)

10:00 Welcome and introduction

10:15 Fracture Orientation Uncertainty is Your Friend! (Provided it is Thoroughly Evaluated)

As a modeller of discrete fracture network models, one usually gets tables with given orientation data gathered by mapping geologists. Seldom these data are questioned by the modeller but rather taken as definite. This may lead to spurious inferences and hence fracture models that do not accurately reflect the true condition of the rock mass.
Uncertainties are not only stemming from tool imprecision, but to a larger extent from external disturbances and human factors. By systematically identifying all relevant sources of uncertainty, that may affect the measured value, and estimate their individual contributions, it is possible to infer an aggregated probability space of the orientation for each single object. This can be expressed as a rough one-parameter dihedral angle measure, Ω, or as a non-parametric surface on a lower hemisphere stereonet, Χ.
The one-parameter representation is well suited for the analysis of large datasets, e.g. to discriminate observations with large uncertainty. In contrast, the non-parametric visualization is useful when examining individual or a few structures that e.g. are in conflict with the established conceptual understanding of the rock mass. The uncertainties may also be used for inverse modelling workflows to evaluate more accurate input parameters for fracture network models.

Speaker: Martin Stigsson (SKB)

Uncertainty_is_your_friend__Provided_it_is_thoroughly_evaluated.pptx

10:35 Challenges of DFN Generation in Complex Geological Models: The Äspö HRL Example

This presentation describes the generation of a discrete fracture network (DFN) model for the Äspö Hard Rock Laboratory based on geological and structural data published by SKB. A three‑dimensional geological model derived from SKB site descriptive reports provides the structural framework for DFN construction. Fracture sets are generated consistently with this model and used to derive an equivalent porous medium for groundwater flow simulations with the code d3f++. The contribution focuses on the modelling workflow and on challenges arising from the complex geological geometry and its impact on DFN generation.

Speaker: Anne Gehrke

20260609_DFN_Modelling_Workshop_AspoSDM.pdf

10:55 Evaluating DFN Generation Methods for Fracture Network Topology in Crystalline Rock

Numerical subsurface models rely on relevant input data and modelling methods to generate robust representations of fluid flow in fractured rock systems.
In this study, a comprehensive discrete fracture network (DFN) modelling workflow is developed using photogrammetric data acquired from an open-pit mine in a crystalline complex in Germany. Several DFN generation methods (tracemap extrusion, fracture growth, geometric) are applied and compared with the aim of identifying the most suitable approach for representing fracture network topology, which is a key control on fluid flow in crystalline rocks.
The results highlight how alternative modelling approaches influence the resulting network topology and, consequently, the representation of connectivity in three-dimensional space.
This presentation aims to initiate discussion on key challenges in DFN modelling, particularly regarding fracture network topology, the conversion of two-dimensional observations into three-dimensional representations, and the strengths and limitations of available software tools.
Publication: https://www.tandfonline.com/doi/full/10.1080/00295450.2025.2581510#d1e514

Speaker: Dr Sarah Weihmann (Chair of Repository Safety, RWTH Aachen University)

dfn_logo_circle.png

DFN-Workshop_V2.pdf

DFN-Workshop_V2.pptx

11:15 Coffee break

11:45 FracLab: A Robust 3D DFN Generator for Coupled Process Modelling for Fractured Media

We developed FracLab, a robust and powerful 3D discrete fracture network (DFN) generator for high-quality fracture networks, which can enable complex numerical simulation of coupled processes. FracLab incorporates optimized geometry trimming and enhanced rejection criteria to generate high-quality 3D DFNs, enabling robust mesh generation for both fractures and rock matrices; it also regulates minimum element size, reduces mesh element count, and improves mesh quality via full-domain geometry optimization, thereby enabling efficient 3D multiphysics simulations that can capture nonlinear geomechanical deformations, local stress variations, fracture-matrix interactions, and stress-dependent fluid flow and solute transport in densely fractured media.

Speaker: Chuanyin Jiang (Uppsala University)

12:05 Hydro-mechanical coupling in deposition tunnels

Water inflow into subsurface excavations in crystalline fractured rock is a complex problem, largely due to hydromechanical coupled processes associated with excavation. Field experiments can exhibit scale effects, where inflow into excavations can be less than predicted based on observations from smaller diameter holes. This work uses a recent study examining flow through a single fracture subject to normal loading, which indicates a stress dependent reduction in transmissivity. This relationship is implemented within a small scale DFN model representing a deposition tunnel/hole. The approach includes spatial variations in stress induced by excavation, allowing transmissivity to evolve as a function of normal stress acting on individual fractures. Stress normal to individual fractures is calculated and transmissivity corrections are applied based on the local stress sate. These corrections depend both on fracture orientation and the in-situ stress field. A range of realisations are used to evaluate the ability of this approach to predicting inflow into deposition tunnels accounting for the excavation influence zone. In addition, the impact of internal transmissivity heterogeneity is investigated compared against the conventional assumption of uniform in-plane transmissivity. The results aim to clarify whether stress dependent transmissivity improves inflow predictions when upscaling from boreholes to larger excavations.

Speaker: Brandon Stock (Stockholm University)

DFN_workshop26_Stock.pdf

DFN_workshop26_Stock.pptx

12:25 Fracture Trace-Constrained Conditional Simulation for 3D Fracture Network Extrapolation: Application to Nuclear Waste Repository Development

Accurate representation of 3D fracture networks is fundamental to risk assessment and design optimization in underground engineering, especially for nuclear waste geological disposal projects where positioning of deposition holes in tunnels is a major issue. This work presents a new conditional simulation framework for trace-constrained DFN extrapolation. A systematic classification of fracture-observation object intersection types is proposed, and case-specific conditioning strategies are developed to enhance the adaptability and accuracy of the simulation. To verify the framework, a synthetic reference DFN resembling real repository conditions is considered, and a stepwise conditioning approach that mimics the progressive availability of fracture trace data during actual construction processes is examined. Results demonstrate that the proposed framework not only strictly honors the observed trace data but also maintains the global and local statistical characteristics of fractures. Importantly, the progressive integration of conditioning data significantly reduces the uncertainty in determining spatial distributions of large fractures. This framework offers a practical and efficient tool for DFN extrapolation, supporting subsequent groundwater inflow assessment and deposition-hole siting decisions in the development of deep geological disposal of nuclear waste.

Speaker: Chuanyin Jiang (Uppsala University)

Talk2 Conditioning.pdf

13:00 → 14:15 Lunch break

Various options

14:15 → 15:35 Presentations: Afternoon

Convener: Nikolas Ovaskainen (Geological Survey of Finland)

14:15 Numerical simulation of damage evolution around the PF/PF-A experiment borehole in faulted Opalinus Clay

The Progressive Failure (PF/PF-A) Experiment at the Mont Terri Underground Rock Laboratory offers a unique opportunity to investigate damage evolution around underground openings in faulted Opalinus Clay under in-situ stress conditions. We present a 3D numerical modelling framework developed to simulate progressive failure in structurally complex clay shale and its long-term evolution subject to hydro-mechanical effects. The approach integrates a site-constrained discrete fracture network, explicit fault zone representation, and anisotropic material behaviour within a discontinuum formulation to capture structurally controlled damage processes around an experiment borehole. The simulations capture stress redistribution, fracture reactivation, and the emergence of a characteristic inner-outer damage zone structure governed by fault–fracture interactions and structural orientation. Sensitivity analyses demonstrate the importance of fault–borehole geometry in controlling damage localisation and extent. Ongoing model developments incorporate coupled hydro-mechanical processes, including suction-driven desaturation and effective stress evolution, to better represent the experimental conditions. Preliminary coupled simulation results indicate that hydraulic effects significantly influence near-borehole damage initiation and spatial distribution. Our modelling framework provides a physics-based tool for interpreting PF/PF-A experimental observations, with important implications for the safe design and performance assessment of nuclear waste disposal in Opalinus Clay.

Speaker: Muhammad Raharsya Andiva (Uppsala University)

Workshop_DFN_090626.pdf

Workshop_DFN_090626.pptx

14:35 From classical DFN flow problems to coupled thermal-hydrological and transport challenges

Modelling flow and transport in discrete fracture networks (DFNs) has developed considerably over the past decades, yet the field continues to be reshaped by new conceptual challenges, computational advances, and emerging applications. This talk provides a personal perspective on the evolution of DFN modelling, from foundational concepts to current challenges and future directions.

A central theme is flow channelling and transport using a Lagrangian framework, where particle travel times and transport resistance provide intuitive measures of transport variability and solute retention in fractured rock. Results from stochastic DFN ensembles highlight how fracture connectivity and small-scale heterogeneity can produce early arrivals, long-tailed breakthrough behaviour, and large variability between network realisations that conventional continuum approaches often fail to capture.

A second theme concerns coupled thermal-hydrological freeze-thaw processes relevant to future cold-climate conditions. Seasonal permafrost dynamics and glacial loading can strongly alter groundwater flow, transport pathways, and fracture properties over timescales ranging from seasons to glacial cycles.

The talk concludes with perspectives on key open challenges, including internal fracture heterogeneity, coupled TH/THM processes, and stochastic upscaling of flow and transport in fractured rock systems.

Speaker: Andrew Frampton (Department of Physical Geography, Stockholm University, Sweden)

DFN Workshop Uppsala v2 - Frampton.pptx

14:55 Hydraulic Fracturing by Supercritical CO2 Injection Considering Rock Microstructure

Supercritical CO2 fracturing is expected to create more complex fracture networks than water-based counterparts, thereby improving the permeability and heat extraction in geothermal reservoirs. The underlying fracture mechanisms driven by this low-viscosity fluid may differ from conventional hydraulic fracturing. In this study, we develop a stabilized hydromechanical phase-field fracture model to simulate hydraulic fracturing in two- and three-dimensional polycrystalline microstructures. To address numerical instabilities caused by strong heterogeneity and operator splitting, we propose a novel spatial stabilization term for the monolithic solution of the coupled hydromechanical problem. We then conduct numerical simulations of hydraulic fracture evolution considering rock microstructure under water and supercritical CO2 injection. Our numerical results reproduce laboratory observations and demonstrate that the generation of complex fracture networks is controlled by both rock heterogeneity and fracturing fluid. Our findings further confirm that supercritical CO2 fracturing is more likely to trigger remote activation of heterogeneous interfaces, leading to more complex fracture morphologies.

Speaker: Weihong Yuan

DFN_Weihong.pdf

15:35 → 17:05 Networking event

Surprise!

19:00 → 21:00 Dinner Kottkokochbar

Menu 1
Toast Skagen (G)
Toasted bread, lemon, pickled onions, horseradish
Grilled Petit tender, French fries, Bèarnaise sauce, Tomato salad
420Kr per/person

Menu2
Asparagus ,Browned butter emulsion, hazelnuts, herbs
Grilled Char Smashed potatoes, Sandefjordsauce, Asparagus, Grilled lemon, Spring veggies
420Kr per/person

Menu 3
Raw beef Pickled beets, silver onion, dijonnaise, deep fried Jerusalem artichoke
Deer, Baby topside Morel sauce,Västerbotten cheese pure, Tomato salad (L)
450kr per/person

Vegetarian Menu
Asparagus,Browned butter emulsion, hazelnuts, herbs
Roasted Beets Celeriapure`, almond, pickeld , pumpkin, Goatcheese, caper
330kr per/person

Wednesday 10 June

10:00 → 13:00 Demos/Hackathons: Morning

Convener: Nikolas Ovaskainen (Geological Survey of Finland)

10:00 An introduction to PorePy for flow simulations

We give an introduction to the open-source research software PorePy, which is a multiphysics simulation framework primarily aimed at fractured porous media. PorePy provides (semi)automatic mesh generation for complex fracture networks and comes with a set of multiphysics simulation setups that are ready to run and can easily be adapted to user demands. The framework emphasizes robust formulations and numerical methods and aims to faithfully follow the mathematical description of the governing processes (e.g., conservation of mass). PorePy is in part built as a library, where some parts (e.g. meshing) can be extracted and combined with other software in wider workflows.

For the demonstration, we will provide jupyter notebooks that allow users to get going with setting up PorePy simulations, targeting flow and transport processes in DFN geometries. The material will be made available through GitHub Codespaces (which require only a GitHub account, no local installation) and through a Docker container. A script for local installations on Linux systems can also be made available.

Speaker: Eirik Keilegavlen (University of Bergen)

11:15 Coffee break

13:00 → 14:00 Lunch break

14:00 → 17:00 Demos/Hackathons: Afternoon

Convener: Nikolas Ovaskainen (Geological Survey of Finland)

14:00 Simulating DFNs and fracture-scale processes using OpenGeoSys

We will go through examples for simulating flow and transport in stressed fractures using OpenGeoSys. This will be done in a browser-based setting, so no prior installation is required this time. The examples include

• pathway-dominated flow through a rough fracture
• brittle fracture propagation in triaxial stress states using phase-field models

Other examples are available. Participants can put their focus according to their interest.

Speakers: Thomas Nagel (TU Bergakademie Freiberg), Dr Mostafa Mollaali (TU Bergakademie Freiberg)

15:30 Coffee break

19:00 → 21:00 Dinner Tapas Iberico

Joint payment required: Check final participant number

Thursday 11 June

10:00 → 12:45 Presentations

Convener: Nikolas Ovaskainen (Geological Survey of Finland)

10:00 Input Data for DFN Modelling: Research Data and Deterministic Modelling

This presentation examines how research data is used for deterministic models, which act as input information in Discrete Fracture Network (DFN) modelling. It highlights how geological, hydrogeological and geophysical observations and measurements are interpreted, structured, and translated into deterministic representations, forming the basis for DFN generation.

Speaker: Antti Joutsen (Posiva)

11:00 From fracture data to DFN for the Safety Case

DFN-based modelling is essential for capturing the heterogeneity of the bedrock and enabling credible mechanical, flow, and transport modelling of the site. This presentation examines how fracture data are translated into discrete fracture network (DFN) models to support the safety case for a geological repository, with a focus on flow and transport pathways in fractured rock. The central challenge is not only to describe fracture geometry, but also to determine which fractures are hydraulically connected and actively carry flow. The application of DFN modelling at Olkiluoto is illustrated through examples from Posiva’s latest safety case.

Speaker: Antti Poteri

11:30 Coffee break

12:00 Bridging DFN and impact of operational phase modelling

DFN modelling has been extensively used in Posiva’s safety case to represent fracture-controlled flow and transport across scales, capturing system behavior with a high level of complexity and detail. However, its computational demands limit its applicability in operational decision-making during the repository lifecycle. In contrast, current modelling on impact of construction and operations relies on simplified, site-scale representations, with local heterogeneity incorporated as observed. While this enables efficient simulations and supports operational use, it leaves uncertainties in unobserved regions and provides limited resolution both at site scale and between known fracture zones.
DFN modelling is therefore needed to extend heterogeneity into less constrained regions and to provide the level of detail required for tunnel section scale analysis. The key challenge is to integrate DFN approaches into the workflow in a sufficiently lightweight and practical manner to support routine predictions and decision-making.
This presentation introduces a synthetic example of a tunnel section scale situation requiring modelling input to support operational decision-making. To begin, conservative assumptions are used to approximate transport-relevant geometries. The central question to the group is whether DFN modelling could be applied in a lightweight way to better represent these conditions and improve the solution.

Speaker: Virve Iisalmi (Posiva Oy)

12:45 → 14:00 Lunch

14:00 → 14:30 Closing discussion and field trip info

Friday 12 June

08:30 → 10:00 Travels to Forsmark

Pick up of excursion participants from Uppsala Central Station at 8:30. Arrival at Forsmark 10:00. Travel by two minibuses (9 people each) and one car (5 people).

10:00 → 11:00 BR&HP How does a core look like and what do we get out of it

11:00 → 12:00 BR&HP Geological mapping of the extension of the SFR facility, how do we do it and what data can you expect

12:00 → 13:00 Lunch

13:00 → 14:30 BR&HP Field visit to the Pool frogs and Liparis loeselii

14:30 → 16:00 Travels back to Uppsala