Underground Research Laboratory Research Articles

Relationship among the fault transmissivity, flow dimension, and effective hydraulic conductivity in siliceous mudstone of the Wakkanai Formation around the Horonobe Underground Research Laboratory in Japan

Effective hydraulic conductivity is typically used for evaluating groundwater flow in faulted/fractured media. Estimating effective hydraulic conductivity relies on modelling the transmissivity and hydraulic connectivity of faults/fractures from a large dataset. As an alternative for evaluating hydraulic connectivity, flow dimension is an easily available and quantitative indicator of fault/fracture hydraulic connectivity. However, the flow dimension has not been used quantitatively as much to evaluate the effective hydraulic conductivity. This study demonstrates how flow dimensions in poorly self-sealed faults directly relate to the effective hydraulic conductivities. The effective hydraulic conductivities in massive siliceous mudstone of the Wakkanai Formation around the Horonobe Underground Research Laboratory in Japan were analysed by simulation with long-term (over 10 years) data of hydraulic pressure and inflow during its construction and operation. The estimated effective hydraulic conductivities varied from ≈10 −8 to ≈10 −11 m s -1 with an increasing depth from ≈250 to ≈600 m. The fault local transmissivities and flow dimensions from packer tests varied from ≈10 −6 to ≈10 −10 m 2 s -1 and from ≈2.0 or more to ≈1.0 with increasing depth, respectively. When applying Landau–Lifshitz–Matheron's formula to calculate the fault effective transmissivities, these variations correlate well, and the estimated effective hydraulic conductivities are sound. Thematic collection: This article is part of the Sustainable geological disposal and containment of radioactive waste collection available at: https://www.lyellcollection.org/topic/collections/radioactive

VR-EX — An immersive virtual reality serious game for science communication about the electrical resistivity tomography measurements in the Mont Terri Rock Laboratory, Switzerland

This paper presents the design, implementation, and evaluation of VR-EX, a combination of a virtual field trip and a serious game in immersive virtual reality. The application’s purpose is the communication of research conducted in the Mont Terri underground research laboratory in Switzerland. VR-EX enables users to actively attend electrical resistivity tomography measurements within a geological experiment, from planning to execution to analysis of the results, and in this way implements an active and playful learning approach. The work conducted in underground research laboratories has a high relevance for society as it contributes to research on the final disposal of nuclear waste. Therefore, the active communication of research methodology and results is crucial to increase understanding of scientific processes and boost interest. VR-EX was evaluated in a user study with 35 participants to measure its overall quality and its effectiveness of the knowledge transfer. Taking the evaluation’s qualitative results into account, the application was improved in an iterative process. Overall, the results prove the good quality of the application and its high effectiveness in terms of knowledge transfer. The reported high engagement, joy, and immersion indicate the benefits of employing immersive virtual reality for vivid science communication.

State of the Engineered Barrier System and host rock of the HE-E experiment after 12 years of heating

This paper presents the status of the HE-E heater experiment, which is currently running at the Mont Terri Underground Research Laboratory (URL) in Switzerland. The experiment is located in a 10 m-long section of a micro-tunnel in the shaly facies of the Opalinus Clay and includes two 4 m-long heater sections isolated by plugs. Heater 1 is located in a sand/bentonite (65/35) buffer section and Heater 2 is located in a granular bentonite buffer section. Heating started on 28 th June 2011, and this paper reports results up to 30 th June 2023. During the 12 years of heating the system has otherwise been left undisturbed with ongoing but very slow resaturation from the Opalinus Clay. The observed response to heating is considered in two phases 1) the initial transient period of about 500 days when heater temperatures rose to the target 140°C and 2) the subsequent evolution. Recently a novel telescoped drilling procedure has been performed to recover and characterize material from the bentonite buffer without interruption of the heating. This paper describes the experimental long-term evolution and status prior to this disturbance, together with expectations regarding the current state of the buffer. Thematic collection: This article is part of the Sustainable geological disposal and containment of radioactive waste collection available at: https://www.lyellcollection.org/topic/collections/radioactive Supplementary material: https://doi.org/10.6084/m9.figshare.c.7186450

Multi-stage micrite diagenesis in the late Jurassic of the Eastern Paris Basin: petrophysical and mechanical properties for engineering purposes

Abstract The Calcaires du Barrois Formation is a succession of dominantly micritic limestone of Kimmeridgian to Tithonian age, outcropping in the eastern part of the Paris Basin. This is an active karstic aquifer of interest to Andra (French National Agency for Radioactive Waste Management), who are studying the feasibility of a deep geological repository of radioactive waste in an underground research laboratory located approximately 450 m below the surface. Surface installations of the Industrial Centre for Geological Disposal project are planned in the upstream recharge zone of the aquifer. It is of primary interest to characterize the Calcaires du Barrois Formation to provide guidelines for the planning and sizing of these facilities, to minimize the impact on the aquifer system. An integrated study was designed for this purpose, linking petrography (thin section and scanning electron microscopy), carbon and oxygen stable isotope geochemistry, X-ray diffraction, petrophysics and geomechanics. It is based on the analysis of three key cored wells penetrating the formation at different relative depths. The Calcaires du Barrois have undergone several stages of diagenesis that have defined the current properties. Unconformities associated with the Jurassic–Cretaceous transition led to prolonged early subaerial exposures during which freshwater flowed efficiently through the upper half of the formation. Through mineralogical stabilization, among other processes, microporosity was preserved in micrites in this interval consisting of clean limestone with thin marl layers. The lower half of the formation, more argillaceous, was not or was only slightly affected by this early meteoric diagenesis, and recrystallization and cementation of micrites occurred during burial diagenesis, involving chemical compaction. Later, during the return to the surface associated to the Cenozoic orogens, another phase of meteoric diagenesis affected the uppermost few metres below the outcropping portions of the formation, but without modifying significantly the previously acquired petrophysical properties. Consequently, an intra-formational boundary was progressively developed at around 75 m (from the top reference). This boundary separates (1) a lower half of the Calcaires du Barrois with dense and tight micrites, showing high Young's modulus values, and a moderate intensity of fractures, from (2) an upper half with microporous micrites showing low Young's modulus values, and almost devoid of fractures. A transitional zone of about 30 m thick, with intermediate properties, sitting above this boundary and below the only thin metre-scale macroporous grainstone level of the formation, accommodated most of the deformation linked to the Cenozoic Western European orogens and is intensively fractured. The current hydrogeological model considers a purely sedimentological boundary to delimit two sub-aquifers within the Calcaires du Barrois Formation. This will have to be reappraised since it is here demonstrated that the real boundary is located significantly higher in the formation and is inherited from a multi-stage diagenetic history. These findings will complement and influence planning for the Industrial Centre's project.

Model Development for Thermal-Hydrology Simulations of a Full-Scale Heater Experiment in Opalinus Clay

Disposal of commercial spent nuclear fuel in a geologic repository is studied. In situ heater experiments in underground research laboratories provide a realistic representation of subsurface behavior under disposal conditions. This study describes process model development and modeling analysis for a full-scale heater experiment in opalinus clay host rock. The results of thermal-hydrology simulation, solving coupled nonisothermal multiphase flow, and comparison with experimental data are presented. The modeling results closely match the experimental data.

Physical properties variations in a shaly formation across a fault core

Summary Faults in general, and in clay materials in particular, have complex structures that can be linked to both a polyphased tectonic history and to the anisotropic nature of the intact rock. Drilling through faults in shaly materials allows measuring properties such as the structure, mineralogical composition, stress orientation and physical properties. We combine different petrophysical measurements on core samples retrieved from a borehole drilled perpendicularly to a fault zone affecting Toarcian shales from the Tournemire underground research laboratory (France). The borehole is cross-cutting the entire fault thickness which is of the order of ten meters. We perform several types of measurements: density, porosity, saturation directly in the field, and P-wave velocities together with P-waves anisotropy on core samples taken at regular intervals. Special protocols were developed to preserve as much as possible the saturation state of the samples. From our measurements, we were able to track the increase of damage, characterized by a smooth decrease in elastic moduli from the intact zone to the fault core. We then calculated Thomsen's parameters to quantify the elastic anisotropy evolution across the fault. Our results show strong variations of the elastic anisotropy with the distance to the fault core as well as the occurrence of anisotropy reversal.

Assessing Sensor Integrity for Nuclear Waste Monitoring Using Graph Neural Networks.

A deep geological repository for radioactive waste, such as Andra's Cigéo project, requires long-term (persistent) monitoring. To achieve this goal, data from a network of sensors are acquired. This network is subject to deterioration over time due to environmental effects (radioactivity, mechanical deterioration of the cell, etc.), and it is paramount to assess each sensor's integrity and ensure data consistency to enable the precise monitoring of the facilities. Graph neural networks (GNNs) are suitable for detecting faulty sensors in complex networks because they accurately depict physical phenomena that occur in a system and take the sensor network's local structure into consideration in the predictions. In this work, we leveraged the availability of the experimental data acquired in Andra's Underground Research Laboratory (URL) to train a graph neural network for the assessment of data integrity. The experiment considered in this work emulated the thermal loading of a high-level waste (HLW) demonstrator cell (i.e., the heating of the containment cell by nuclear waste). Using real experiment data acquired in Andra's URL in a deep geological layer was one of the novelties of this work. The used model was a GNN that inputted the temperature field from the sensors (at the current and past steps) and returned the state of each individual sensor, i.e., faulty or not. The other novelty of this work lay in the application of the GraphSAGE model which was modified with elements of the Graph Net framework to detect faulty sensors, with up to half of the sensors in the network being faulty at once. This proportion of faulty sensors was explained by the use of distributed sensors (optic fiber) and the environmental effects on the cell. The GNNs trained on the experimental data were ultimately compared against other standard classification methods (thresholding, artificial neural networks, etc.), which demonstrated their effectiveness in the assessment of data integrity.

Modelling of failure and fracture development of the Callovo-Oxfordian claystone during an in-situ heating experiment associated with geological disposal of high-level radioactive waste

To ensure the safety of geological disposal of high-level radioactive waste, in-situ experiments have been carried out to examine the behavior of rocks in underground research laboratories (URLs). At the Meuse/Haute-Marne URL in France, the French National Radioactive Waste Management Agency (Andra) has been assessing the Callovo-Oxfordian claystone (COx) as potential host rock of geological disposal by subjecting the COx to in-situ heating mimicking exothermic radioactive waste. Results of the in-situ experiments are used to validate and bolster the numerical simulators for predicting the thermo-hydromechanically (THM) coupled behavior of the COx. The numerical simulators are, however, yet to be tested for predicting the failure and fracture development of the COx during heating, which is of paramount importance to the safety of the geological disposal. In this research, we modelled a recently carried out in-situ experiment at the Meuse/Haute-Marne URL using the TOUGH-FLAC simulator to predict the failure and fracture development of the COx during heating. The objectives are to examine the effects of (i) the weak bedding planes, (ii) the softening rate of matrix/weak plane strengths, and (iii) the stiffness anisotropy of the COx on the development of shear and tensile fractures during heating. Results show that considering failure along the weak planes enabled accurate predictions of fracture development. Also, fracture development intensified at a softening rate beyond a threshold level and the geometry of fractures was significantly affected by the stiffness anisotropy. These results will help boost the reliability of the safety and performance assessment of geological disposal in claystone.

"Feels Like an Indie Game"-Evaluation of a Virtual Field Trip Prototype on Radioactive Waste Management Research for University Education.

This article describes the design and evaluation of a virtual field trip on the topic of radioactive waste management research for university education. We created an interactive virtual tour through the Mont Terri underground research laboratory by enhancing the virtual experiment information system, designed for domain experts, with background information, illustrations, tasks, tests, and an improved user interface. To put the tour's content into context, a conventional introductory presentation on the final disposal of radioactive waste was added. A user study with 22 participants proved a good perceived usability of the virtual tour and the virtual field trip's ability to transfer knowledge. These results suggest a benefit of employing virtual field trips in geoscientific university courses. In addition, it is conceivable to use the virtual field trip as a tool for science communication in the context of participatory processes during nuclear waste disposal site selection processes.

The French Underground Research Laboratory in Bure: An Essential Tool for the Development and Preparation of the French Deep Geological Disposal Facility Cigéo

The French Underground Research Laboratory in Bure: An Essential Tool for the Development and Preparation of the French Deep Geological Disposal Facility Cigéo

Design-of-Experiment (DoE) based history matching for probabilistic integrity analysis—A case study of the FE-experiment at Mont Terri

We present an application of design-of-experiment (DoE) based history matching as an approach to reduce and investigate parameter uncertainties in finite-element models for repositories of high-level radioactive waste. We combine experimental data from the FE-experiment at the Mont Terri underground research laboratory in Switzerland with thermo-hydro-mechanical modeling using the open-source package OpenGeoSys. Uncertainties were reduced by an initial parameter screening to find heavy hitters and an experiment-matching procedure using Monte-Carlo sampling on a Gaussian proxy model to fit the error between modeling response and the experiment. Furthermore, we performed a global sensitivity analysis based on the proxy model, demonstrating the spatial impact of parameter sensitivities. Very good agreement between the experimental data and the model was found for the temperature response, whereas the pressure match hints at a significant remaining gap in the physical models and/or structure. This gap could not be filled within the scope of our contribution and needs further investigation.

Using multiple isotopes to determine groundwater source, age, and renewal rate in the Beishan preselected area for geological disposal of high-level radioactive waste in China

Understanding hydrogeological conditions is crucial for selecting and assessing the long-term safety performance of a high-level radioactive waste (HLW) disposal repository. Utilizing environmental isotopes as effective markers for analysing groundwater movement, this study investigates groundwater recharge sources, age, and renewal rates using multiple isotopes in China's potential HLW repository site, the Beishan area. The results indicated deep bedrock groundwater primarily derives from ancient precipitation infiltration under cold climatic conditions. A noteworthy distinction is that loose sedimentary groundwater exhibits higher tritium content (>10 TU) compared to bedrock groundwater (<3.2 TU). Groundwater within the recharge area, especially within gullies and piedmont slope deposits, is relatively youthful, with an age of less than 30 years and an annual renewal rate exceeding 5 %. In contrast, the shallow groundwater age in the intermountain basins and depressions of the discharge area generally exceeds 50 years, with an annual renewal rate often falling below 0.5 %. At the Beishan underground research laboratory site, deep groundwater at the disposal repository depth displays a corrected 14C age exceeding 8,000 years, indicating an extremely slow movement and alteration rate. As a result, the hydrogeological conditions in the Beishan area are expected to be relatively beneficial for ensuring the safety of HLW repository.

Countermeasure for reduction of groundwater inflow and construction of the Mizunami Underground Research Laboratory

Countermeasure for reduction of groundwater inflow and construction of the Mizunami Underground Research Laboratory

A thermomechanical model for argillaceous hard soils–weak rocks: application to THM simulation of deep excavations in claystone

The paper presents the enhancement of an existing constitutive model for argillaceous hard soils–weak rocks to incorporate non-isothermal conditions, to be used in coupled thermo-hydro-mechanical (THM) simulations of underground excavations subjected to temperature variations within the context of deep geological nuclear waste disposal. The proposed thermo-elastoplastic extension accounts for the effect of temperature on the yield and plastic potential functions and on the elastic stiffness. The resulting model is validated through the simulation of relevant non-isothermal laboratory tests reported in the literature. The model is then applied to the coupled THM simulation of an in situ heating test conducted at the Meuse/Haute-Marne underground research laboratory in Bure, France, excavated in the Callovo-Oxfordian claystone. Results show that the incorporation of thermal effects into the constitutive description of the host rock plays a significant role in the behaviour of the excavation when subjected to thermal loading, particularly in the evolution of the excavation fractured zone.

Evaluation of EDZ characterization technology for URL based on field investigation at BET

Detailed characterization of the Excavation Damage Zone (EDZ) is an important issue for the high-level radioactive waste (HLW) geological disposal engineering, which is closely related to the long-term safety of the HLW repository. With drill-blast experiment in Beishan Exploration Tunnel (BET, a platform for the field experiment and validation of potential technologies used for China’s HLW disposal engineering in crystalline rock), systematic field tests were carried out to evaluate the suitability of techniques in characterizing EDZ, and to study EDZ characteristic in crystalline tunnel. A series of investigation technologies were used to delineate EDZ and to examine the process of its formation, which includes: p-wave velocity measurement, ground penetrating radar (GPR), acoustic emission (AE) monitoring and borehole televiewer. P-wave velocity measurement along borehole reveal that wave velocity decreased significantly (more than 10%) in 30 cm to 50 cm from the excavation surface, and this zone is defined as EDZ. Clear images of borehole televiewer were obtained, which is helpful for EDZ delineation. GPR and borehole radar were also used for EDZ delineation. Strong reflection signals were detected in the range of 10 cm to 25 cm by GPR with high frequency antenna, indicating significant changes of physical properties of rock-mass in the zone, which is defined as Highly Damaged Zone (HDZ). Moreover, the formation process of EDZ induced by blast in crystalline rock tunnel was analyzed using AE monitoring. Damage process of surrounding rock was divided into blasting damage stage and progressive damage stage. AE events location show the induced cracking activities were clustering within 30 cm to 100 cm from excavation surface. With the experience from field investigation and result analysis, the feasibility and suitability of the techniques for EDZ characterization is evaluated. Finally a specialized EDZ characterization technique system is proposed for underground research laboratory construction in crystalline host rock in Beishan area.

Geophysical Survey Applications in Underground Research Laboratories and Deep Disposal Sites of Spent Nuclear Fuel

Geophysical Survey Applications in Underground Research Laboratories and Deep Disposal Sites of Spent Nuclear Fuel

High‐Resolution Characterization of Excavation‐Induced Fracture Network Using Continuous and Discrete Inversion Schemes

AbstractThe Meuse/Haute‐Marne Underground Research Laboratory provides the location for the experiment designed to investigate the induced fracture network around open or sealed galleries and drifts. The objective of this study is to investigate and reconstruct the hydraulic properties and the geometry of the induced fracture network to improve the insights and validate the conceptual model of the induced fracture network due to the stress redistribution during tunnel excavations. Within the presented study, the cross‐hole responses of the pneumatic tests were analyzed in the first step with an equivalent porous media—3D travel time‐based tomographic approach. In the next step selected 2D profiles of the 3D model domain were inverted using a discrete fracture network inversion approach. The database of the tomographic analysis is based on 18 gas injection tests and 151 pressure interferences, which were recorded between nine closely spaced boreholes. The travel time‐based inversion approach allowed for the reconstruction of the 3D gas diffusivity distribution between nine boreholes with high‐resolution. The applied discrete fracture network inversion approach is based on a transdimensional Markov Chain Monte Carlo (MCMC) methodology and it operates with reversible model updates (jumps) that change the problem dimensions, that is, the number, length and position of fractures within the model domain after each iteration step. The synthesis of the results between the reconstructed 3D diffusivity tomogram and the 2D fracture tomograms improved the insights into the spatial geometry of the induced fracture network around galleries.

Stable microbial community in compacted bentonite after 5 years of exposure to natural granitic groundwater.

The Materials Corrosion Test (MaCoTe) at the Underground Research Laboratory in Grimsel, Switzerland, assesses the microbiology and corrosion behavior of engineered barrier components of a deep geological repository (DGR) for long-term disposal of high-level nuclear waste. Diversity and temporal changes of bentonite-associated microbial community profiles were assessed under DGR-like conditions for compacted Wyoming MX-80 bentonite (1.25 g/cm3 and 1.50 g/cm3 targeted dry densities) exposed to natural groundwater. Using culture-dependent and molecular techniques, samples taken from the outside layer of 5-year borehole modules revealed up to 66% and 23% of 16S rRNA gene sequences affiliated with Desulfosporosinus and Desulfovibrio, respectively. Putatively involved in sulfate reduction, these taxa were almost undetectable within the bentonite core. Instead, microbial profiles of the inner bentonite core were similar to uncompacted bentonite used to pack modules years earlier, and were consistent with a previously published 1-year time point, revealing no detectable microbial growth. Abundances of culturable aerobic and anaerobic heterotrophic bacteria in the uncompacted bentonite were relatively low, with less than 1,000 and 100 colony-forming units (CFUs) per gram dry weight, respectively. Nearly 5 years after emplacement, culturable heterotrophic bacterial CFUs and sulfate-reducing bacteria did not change significantly inside the bentonite core. Phospholipid fatty acid data indicated similar lipid abundance, and corresponding cell abundance estimates, for inner 5-year MaCoTe bentonite samples compared to those previously obtained for 1-year incubations. Collectively, our results provide complementary evidence for microbial stability inside highly compacted bentonite exposed to conditions that mimic engineered barrier components of a deep geological repository. IMPORTANCE The long-term safety of a deep geological repository for used nuclear fuel is dependent on the performance of the engineered and natural barriers. Microbial activity can produce chemical species that can influence the corrosion of the disposal containers for used nuclear fuel. Although previous studies have evaluated the microbiology of compacted bentonite clay within subsurface environments, these have been limited to relatively short incubations (i.e., 1 year). The current study provides a unique 5-year perspective that reinforces previous findings of growth inhibition for bentonite clay exposed to in situ subsurface conditions.

Numerical modeling of site-scale groundwater flow with stochastic parameterized hydraulic conductivity fields for geological disposal of high-level radioactive waste in China

Deep geological disposal is internationally accepted as a feasible and safe approach for high-level radioactive waste (HLW) disposal. To evaluate hydrogeological conditions in support of safety assessments for HLW disposal at the Xinchang preselected site in China, stochastic inverse models of site-scale groundwater flow were developed in this study to generate highly parameterized hydraulic conductivity fields for the fractured medium by adopting pilot point and null-space Monte Carlo methods. The hydraulic influence zones of the faults were carefully considered to have homogenous parameter values across the zones. A total of 120 multiple random realizations were generated to characterize the 3D spatial variations in hydraulic conductivity by conditioning to 1218 fixed pilot points. The simulated hydraulic heads of the realizations were in good agreement with observational data. The hydraulic conductivity fields close to the boreholes could be characterized in detail and had relatively low uncertainties. Furthermore, the hydraulic conductivity (K) values around underground research laboratory (URL) at the HLW disposal zone depth were less than 10−9 m/s. The K values obtained for most of the influence zones of these faults at this depth were consistent with hydraulic test data and ranged from 10−10 to 10−9 m/s, thereby indicating that the surrounding rock has low permeability and is suitable for HLW disposal. These findings offer new insights into hydrogeological conditions by providing key information on the permeability characteristics that need further focus on HLW disposal.

Performing science, performative science: a science and technology studies (STS) reflection on the pioneering pathways of the HADES underground research laboratory (URL)

Abstract. Developing and implementing a project for managing high-level radioactive waste over extensive periods of time is a multifaceted challenge. Among others, it entails demonstrating the feasibility, safety and overall performance of the proposed waste management strategy. However, how to tackle such a demonstration when the periods over which the waste needs to be isolated and contained extend over thousands of years? In the development of geological disposal facilities, a key role in this matter is played by underground research laboratories (URLs), which aim to provide a setting to study how different techniques and materials perform in a realistic environment. Insights gained into URLs are expected to be translatable to the performance and timescales of an actual repository, hence offering a tool to make a seemingly distant future comprehensible today. In this contribution, we use the HADES (High-Activity Disposal Experimental Site) URL in Mol, Belgium, as an example to illustrate how URLs are producing knowledge and insights, and how in this way they are also actively performing the possible future(s) of radioactive waste management. Building on insights gained in the field of science and technology studies (STS), this paper emphasizes how knowledge production is a complex process characterized by the interplay of heterogeneous – and sometimes rather trivial – elements and actors interlinked through a range of explicit and implicit decisions. We argue that tracing these elements and decisions, making them explicit and reflecting upon them are of key importance, as knowledge production not only describes a possible future but also actively contributes to “making the future” by emphasizing what is considered possible and imaginable – and what is not. This paper will therefore also focus on what the implications of making the future could entail from an ethical perspective, with a particular focus on deliberation and intergenerational justice.