Underground Laboratory Research Articles

Hydrogeochemical impact of Opalinus Clay system shown in migration lengths of uranium

Abstract. Models and simulations allow a prognosis of how processes in the geosphere might occur in the future by considering physical and chemical processes. They are the only way to test future scenarios and hypotheses and to evaluate how a repository site will develop over a period of a million years, e.g. by quantifying potential radionuclide migration in the hydrogeological system of the containment providing rock unit. An example is used to demonstrate the extent to which simulated migration lengths can vary for a million years, depending on the model concept and on the underlying data and parameters. In the case of uranium in the potential host rock Opalinus Clay (Switzerland), the range extends from 5 m, by applying experimentally determined transport parameters, over 50 m, using process-based approaches and taking hydrogeology into account, and up to 80 m, depending on the thermodynamic data set used. The degree of reliability of the models is derived from comparison with laboratory tests, data from boreholes and underground laboratories or natural analogues. This is the only way to assess the simulation results. In addition, indications can be provided regarding where new data need to be collected. So our task is to find an answer to the following question: how accurate do the models for the repository site search have to be in order to produce resilient and robust forecasts? To reduce the uncertainty related to the migration length of uranium in the Opalinus Clay, the calcite carbonate ion and the hydrogeological system at a potential disposal site need to be known, whereas the quantity of clay minerals plays a subordinate role, as long as it is enough, which is the case in argillaceous formations.

Modelling the viscoplastic behaviour of Callovo-Oxfordian claystone with consideration of damage effect

In order to evaluate the performance of deep geological disposal of radioactive waste, an underground research laboratory (URL) was constructed by Andra in the Callovo-Oxfordian (COx) claystone formation at the Meuse/Haute-Marne (MHM). The construction of URL induced the excavation damage of host formations, and the ventilation in the galleries desaturated the host formation close to the gallery wall. Moreover, it is expected that the mechanical behaviour of COx claystone is time-dependent. This study presents a constitutive model developed to describe the viscoplastic behaviour of unsaturated and damaged COx claystone. In this model, the unsaturation effect is considered by adopting the Bishop effective stress and the van Genuchten (VG) water retention model. In terms of the viscoplastic behaviour, the nonstationary flow surface (NSFS) theory for unsaturated soils is used with consideration of the coupled effects of strain rate and suction on the yield stress. A progressive hardening law is adopted. Meanwhile, a non-associated flow rule is used, which is similar to that in Barcelona basic model (BBM). In addition, to describe the damage effect induced by suction change and viscoplastic loading, a damage function is defined based on the crack volume proportion. This damage function contains two variables: unsaturated effective stress and viscoplastic volumetric strain, with the related parameters determined based on the mercury intrusion porosimetry (MIP) tests. For the model validation, different tests on COx claystone under different loading paths are simulated. Comparisons between experimental and simulated results indicated that the present model is able to well describe the viscoplastic behaviour of damaged COx claystone, including swelling/shrinkage, triaxial extension and compression, and triaxial creep.

Period‐ and Pressure‐Dependent Hydraulic Properties of a Fractured Granite Inferred From Periodic Pumping Tests

AbstractFractures can greatly impact fluid flow and pore pressure distribution in the upper crust. By conducting borehole hydraulic experiments, we can determine the ability of fractures to transport fluids and affect pressure diffusion under in situ conditions. We performed a series of periodic hydraulic tests in a borehole at the Bedretto Underground Laboratory for Geosciences and Geoenergies (Switzerland). We investigated the period‐ and pressure‐dependent response of a fractured granite by controlling the flow rate of harmonic and non‐harmonic oscillations, covering a wide range of periods as well as mean‐ and amplitude‐pressure values. By analyzing the phase and amplitude relation between the flow rate and fluid pressure in the injection interval, we found that the intersected fracture zone exhibits a period‐dependent hydraulic response close to radial flow perturbed by fracture‐related hydromechanical coupling effects. The main features of the interval's hydraulic response were reproduced by an uncoupled diffusion solution for radial flow, which was used to derive apparent hydraulic properties. The largest deviations from this model occur for the phase shifts and correlate with the pressure amplitude. This non‐linear expression of hydromechanical coupling associated with deformable fractures was interpreted in terms of a pressure‐dependent effective compliance of the fractures that affects their effective storativity. The period dependence is likely related to the spatial heterogeneity expected in fractured rocks and the varying sensitivity of the hydraulic response for different periods. Accounting for these effects is necessary for a correct hydraulic characterization in fractured environments and is valuable for inferring fracture mechanical behavior.

The CYGNO experiment: a directional Dark Matter detector with optical readout

We are going to discuss the R&D and the prospects for the CYGNO project, towards the development of an innovative, high precision 3D tracking Time Projection Chamber with optical readout using He:CF4 gas at 1 bar. CYGNO uses a stack of triple thin GEMs for charge multiplication, this induces scintillation in CF4 gas, which is readout by PMTs and sCMOS cameras. High granularity and low readout noise of sCMOS along with high sampling of PMT allows CYGNO to have 3D tracking with head tail capability and particle identification down to O(keV) energy for directional Dark Matter searches and solar neutrino spectroscopy. We will present the most recent R&D results from the CYGNO project, and in particular the overground commissioning of the largest prototype developed so far, LIME with a 33×33 cm2 readout plane and 50 cm of drift length, for a total of 50 litres active volume. We will illustrate the LIME response characterisation between 3.7 keV and 44 keV by means of multiple X-ray sources, and the data Monte-Carlo comparison of simulated sCMOS images in this energy range. Furthermore, we will present current LIME installation, operation and data taking at underground Laboratori Nazionali del Gran Sasso (LNGS), serving as demonstrator for the development of a 0.4 m3 CYGNO detector. We will conclude by mentioning the technical choices and the prospects of the 0.4 m3 detector, as laid out in the Technical Design Report (TDR) recently produced by our collaboration.

Gamma-, neutron-, and muon-induced environmental background simulations for 100Mo-based bolometric double-beta decay experiment at Jinping Underground Laboratory

Gamma-, neutron-, and muon-induced environmental background simulations for 100Mo-based bolometric double-beta decay experiment at Jinping Underground Laboratory

Periodic Variations of the Radon Concentration Measured by the Large Volume Detector at the Gran Sasso Underground Laboratory

Periodic Variations of the Radon Concentration Measured by the Large Volume Detector at the Gran Sasso Underground Laboratory

The 13C(α,n)16O cross section measurement at low energies at LUNA

One of the main neutron sources for the astrophysical s-process is the 13C(α,n)16O. This reaction takes place in thermally pulsing asymptotic giant branch (TP-AGB) stars in a stellar environmental with temperature of about 90 MK. To model the nucleosynthesis process connected with the reaction, it is important the cross section reaction evaluation inside the so called Gamow peak, in the energy window 150-240 keV. In this work the results of the first 13C(α,n)16O direct measurement performed by the LUNA collaboration in the underground laboratory of LNGS are presented.The measurement covers the energy range 230-300 keV, being the first direct measurement to reach the s-process Gamow window. Lower uncertainties with respect to previous measurements in literature are provided and this allows to reduce overall uncertainties on reaction rates calculation. Selected stellar models have been computed to estimate the impact of our revised reaction rate. Using the lower reaction rate at -2σ, for stars of nearly solar composition, we find sizeable variations for some isotopes, whose production is influenced by the activation of close-by branching points that are sensitive to the neutron density, in particular 60Fe, 205Pb and and 152Gd.

About this title - Geological Disposal of Radioactive Waste in Deep Clay Formations: 40 Years of RD&D in the Belgian URL HADES

Over the past four decades, research in the HADES underground research laboratory has demonstrated that the geological disposal of radioactive waste in clay can provide a safe and feasible disposal solution. This Special Publication presents the main contributions of the HADES laboratory to Belgian and international research into geological disposal.

Quantitative assessment and development utilization modes of space resources in closed and abandoned mines

ABSTRACT With the increase of the number of closed and abandoned mines in the world, it has become an urgent need to study the assessment and reuse of various resources of closed and abandoned mines, as well as the transformation and development mode of mines. Various sources of data are used to identify the types of closed and abandoned mine resources, the classification system of aboveground and underground resources of mines is established. The calculation method of available space of ground buildings, underground tunnels and shafts, and the estimation method of underground residual coal quality are given, the determination method of transformation mode of closed and abandoned mines is proposed. The transformation and utilization modes of closed and abandoned mines in China and abroad are compared. Taking a closed mine in Shaanxi Province as an example, the optimal transformation mode is determined and the planning scheme is given. The main conclusions are as follows: (1) Aboveground resources of closed and abandoned mines mainly include surface water, idle land, mining equipment, and buildings of industrial squares and living areas, while underground resources mainly include groundwater, residual minerals, underground space and mining equipment left underground. (2) The aboveground development and utilization modes of closed and abandoned mine resources include mine park, mining museum, industrial relics, etc. while the underground development and utilization modes include underground storage, underground laboratory, energy development, etc. (3) It is calculated that the building space volume of a closed mine industrial square in Shaanxi Province, China is up to 1.04 × 105 m3, the available underground space volume including shaft, roadway, chamber and yard is 1.18 × 105 m3, and the mass of underground residual coal is nearly 56 million tons. (4) Based on the evaluation of suitability for mine transformation, three transformation modes have been identified for a closed mine in Shaanxi Province, China. Through the comprehensive benefit evaluation, the optimal utilization mode for the mine has been determined as mine park and mine museum, and a preliminary planning scheme is proposed. The research on the reuse of the remaining resources of closed and abandoned mines provides a new idea for the transformation and sustainable development of resource-depleted mines, which is of great significance for the realization of the global carbon peak and carbon neutrality.

Progress in biological and medical research in the deep underground: an update.

As the growing population of individuals residing or working in deep underground spaces for prolonged periods, it has become imperative to understand the influence of factors in the deep underground environment (DUGE) on living systems. Heping Xie has conceptualized the concept of deep underground medicine to identify factors in the DUGE that can have either detrimental or beneficial effects on human health. Over the past few years, an increasing number of studies have explored the molecular mechanisms that underlie the biological impacts of factors in the DUGE on model organisms and humans. Here, we present a summary of the present landscape of biological and medical research conducted in deep underground laboratories and propose promising avenues for future investigations in this field. Most research demonstrates that low background radiation can trigger a stress response and affect the growth, organelles, oxidative stress, defense capacity, and metabolism of cells. Studies show that residing and/or working in the DUGE has detrimental effects on human health. Employees working in deep mines suffer from intense discomfort caused by high temperature and humidity, which increase with depth, and experience fatigue and sleep disturbance. The negative impacts of the DUGE on human health may be induced by changes in the metabolism of specific amino acids; however, the cellular pathways remain to be elucidated. Biological and medical research must continue in deep underground laboratories and mines to guarantee the safe probing of uncharted depths as humans utilize the deep underground space.

Fault Zone Spatial Stress Variations in a Granitic Rock Mass: Revealed by Breakouts Within an Array of Boreholes

AbstractThe in situ stress state within fault zones is technically challenging to characterize. At the Bedretto Underground Laboratory in the Swiss Alps, the breakouts observed in an array of eight inclined boreholes penetrating a fault zone offer a unique opportunity to characterize the fault‐associated spatial stress variations. Synthesizing multiple geophysical logs, natural geologic structures intersecting these boreholes are identified, revealing a hierarchy of a major fault zone along with secondary structures. Within the boreholes, breakout rotations occur over multiple scales, spanning individual fractures and the entire major fault zone. We first estimate and rule out the effect of the fracture‐induced anisotropy on the breakout rotations, which are attributed mainly to the stress variations. Based on the stress field around a circular borehole and Mohr‐Coulomb failure criterion, the observed breakout azimuths are used to invert the stress information. Results show that the stress field outside the fault zone features a stress ratio (quantifying the relative stress magnitude) of about 0.9, an inclined overburden stress (inclination: 12°∼18°), and a maximum horizontal principal stress (SHmax) oriented N100∼120°E. Within the fault zone, a substantial reduction of the stress ratio and complicated stress rotations are constrained, likely induced by the stress drop on local fractures. As a result, less critical stress state inside the major fault zone is expected. Our work provides a semi‐quantitative estimation of the in‐situ stress variations around fault zones in the absence of direct stress measurements, which is beneficial to a number of scientific and engineering applications.

Laboratory simulation of fault reactivation by fluid injection and implications for induced seismicity at the BedrettoLab, Swiss Alps

Fluid induced fault reactivation experiments will take place as part of the “Fault Activation and Earthquake Rupture” project (FEAR) at the BedrettoLab, an underground laboratory for geosciences and geo-energy excavated within the Rotondo massif (Swiss Alps). The aim of this publication is to characterize frictional properties and permeability of the main segment of the fault zone selected for limited fluid-induced fault reactivation experiments. Firstly, we characterized fault zone microstructures in the field and in thin sections. Secondly, we assessed fault gouge mineralogy by X-ray powder diffraction analysis, yielding a composition in agreement with similar fault gouges in the same area. Finally, we performed a detailed frictional and permeability characterization in laboratory, using BRAVA (Brittle Rock deformAtion Versatile Apparatus). We performed five frictional experiments, run at the actual in-situ conditions: four experiments for frictional properties characterization; and one further experiment where we stimulated the experimental fault by fluid pressurization applying a similar injection protocol designed for the in-situ hydraulic stimulation experiment. Additionally, we performed microstructural analysis on experimental samples to link frictional and permeability properties with fault fabric evolution. The integration of experimental results with field investigations suggests that the selected fault is potentially seismogenic and can be dynamically reactivated and controlled with hydraulic stimulation. This study highlights the importance of bridging the gap between laboratory and in-situ fault characterization, where experimental results become instrumental for the correct design of injection protocols such as those of FEAR project.

Clay-associated microbial communities and their relevance for a nuclear waste repository in the Opalinus Clay rock formation.

Microorganisms are known to be natural agents of biocorrosion and mineral transformation, thereby potentially affecting the safety of deep geological repositories used for high-level nuclear waste storage. To better understand how resident microbial communities of the deep terrestrial biosphere may act on mineralogical and geochemical characteristics of insulating clays, we analyzed their structure and potential metabolic functions, as well as site-specific mineralogy and element composition from the dedicated Mont Terri underground research laboratory, Switzerland. We found that the Opalinus Clay formation is mainly colonized by Alphaproteobacteria, Firmicutes, and Bacteroidota, which are known for corrosive biofilm formation. Potential iron-reducing bacteria were predominant in comparison to methanogenic archaea and sulfate-reducing bacteria. Despite microbial communities in Opalinus Clay being in majority homogenous, site-specific mineralogy and geochemistry conditions have selected for subcommunities that display metabolic potential for mineral dissolution and transformation. Our findings indicate that the presence of a potentially low-active mineral-associated microbial community must be further studied to prevent effects on the repository's integrity over the long term.

Direct searches of dark matter with the SABRE South experiment

The SABRE (Sodium-iodide with Active Background REjection) South experiment is a direct dark matter detector, made of radio-pure NaI(Tl) crystals surrounded by a liquid scintillator veto. The achievement of ultra-low background rate is essential to provide a model independent test of the signal observed by the DAMA/LIBRA experiment whose claim has not been verified yet. The SABRE South experiment will be located at the Stawell Underground Physics Laboratory (SUPL), Australia, the first deep underground laboratory in the Southern Hemisphere. The laboratory will not only house rare event physics searches but also measurement facilities to support low background physics experiments and applications like radiobiology and quantum computing. The SABRE South detector commissioning is expected to occur in 2023. This paper details the setup and projections for the experiment, and a brief description of the underground laboratory.

Underground laboratories

A brief review on underground laboratories at the time of IDM 2022 is reported. General characteristics of these research infrastructures are discussed and a few highlights from different laboratories are reported. The idea of networking between underground laboratories is discussed.

Status and future prospects of the NEWS-G experiment

The NEWS-G collaboration is searching for light dark matter using spherical proportional counters. Access to the mass range from 50 MeV to 10 GeV is enabled by the combination of low energy threshold, light gaseous targets (H, He, Ne), and highly radio-pure detector construction. Several of the recent developments that have paved the way for the operation of a new 140 cm in diameter, spherical proportional counter are presented. Constructed and commissioned at LSM using 4N copper with a 500\muμxm electroplated inner layer, the detector is now installed in SNOLAB, where it has begun data taking. Building on the electroplating of the current detector, the collaboration construct its next detector directly in the underground laboratory, using ultra-pure copper electroforming. The design and construction of ECUME, a 140 cm in diameter spherical proportional counter fully electroformed underground is discussed, along with the potential to achieve sensitivity reaching the neutrino floor in light Dark Matter searches with a next-generation detector.

The low-energy spectrum in DAMIC at SNOLAB

The DAMIC experiment employs large-area, thick charge-coupled devices (CCDs) to search for the interactions of low-mass dark matter particles in the galactic halo with silicon atoms in the CCD target. From 2017 to 2019, DAMIC collected data with a seven-CCD array (40-gram target) installed in the SNOLAB underground laboratory. We report dark-matter search results, including a conspicuous excess of events above the background model below 200V_{ee}Vee, whose origin remains unknown. We present details of the published spectral analysis, and update on the deployment of skipper CCDs to perform a more precise measurement by early 2023.

Numerical simulations for describing generation of excavation damaged zone: Important case study at Horonobe underground research laboratory

The aim of the present research was to establish a case study for the prediction of the unknown EDZ (Excavation Damaged Zone) distribution using a numerical analysis calibrated by replicating the trends in the EDZ observed from one of the representative underground research fields in Japan (Horonobe URL). In this study, a 2D numerical analysis using a damage model, which can determine rock deformation and fracturing simultaneously, is presented. It was calibrated to reproduce the excavation of the gallery at the Horonobe URL at a depth of 350 ​m. Simulated results show an excellent agreement with the extent of the measured EDZ and capture the failure modes of EDZ fractures suggested by the in-situ observations. Finally, the calibrated numerical analysis was used to realistically estimate the EDZ formation for the geological disposal of high-level radioactive waste (HLW) under the same environment as that of the above-mentioned galley at the Horonobe URL. Consequently, it was shown that the tensile/shear hybrid fractures dominantly constituted the EDZ and propagated to a maximum extent of about 0.3 ​m from the cavity wall during the cavity excavation for the HLW disposal. Overall, the calibrated numerical analysis and resulting estimations, targeted for the environment at the depth of 350 ​m at the Horonobe URL, where mudstone is located, should be useful for predicting the trends in the EDZ distribution expected in the implementation of HLW disposal projects under deep geological conditions, such as those that exist in Japan, which are dominated by sedimentary rocks, including mudstone.

Challenges Related to the Transformation of Post-Mining Underground Workings into Underground Laboratories

Underground mines are a vital part of the European raw material industry. The subsurface mining process is related to the large-scale development of underground structures like tunnels, chambers, workings, etc. These structures are abandoned or liquidated during the process of exploitation or after the termination of works. Still, due to the unique environment, post-mining facilities may be adopted for different purposes. There are few examples of implementations of this capacity in practical terms such as underground laboratories (ULs), energy storages, landfills of dangerous wastes, or food production plants. Unfortunately, the unique environment offered by underground space is also related to the occurrence of exceptional hazards, like seismicity and ground control problems, gases, floods, the lack of natural ventilation, and high temperatures. This results in low interest in investing in such facilities. Within this paper, some ways to repurpose underground mines have been presented, and possible challenges that need to be faced have been described. An extensive database of threats to post-mining repurposing and ways to mitigate them has been prepared based on surveys and interviews conducted with representatives of currently existing Uls and mining companies and a literature review. Finally, this manuscript provides a general look at post-mining infrastructure in Europe’s current situation and in the future.

Continuous Gravity Observations at Mt. Somma-Vesuvius with a gPhoneX Gravimeter: In-Depth Instrumental Response Characterization and Tidal Model

We report on the results of about 9 months of gravimetric recordings acquired at Mt. Somma-Vesuvius (SV) volcano (Southern Italy) with the new generation relative gravimeter gPhoneX#116 (gPh#116), which is a gravimeter specifically designed for continuous gravity recording. We also present the outcomes of an intercomparison experiment of the gPhone#116 conducted at the J9 gravity observatory in Strasbourg (France). In this intercomparison, we were able to check the scale factor of the meter with a high degree of precision by means of an intercomparison with 2 superconducting gravimeters (SGs) and a FG5-type absolute ballistic gravimeter. Multiple calibration approaches allowed us to validate the manufacturer's original calibration constants to a level of 1% accuracy and 0.1% precision. Moreover, we carried out a comparative study of the noise level of the gPh#116 with respect to the SGs and other spring meters routinely used in both prospecting and time-lapse gravimetry. It turns out that gPh#116 exhibits lower levels at hourly time-scales than other compared spring gravimeters (Graviton, gPhone#054, Scintrex-CG5). It was also possible to carry out a detailed study of the instrumental drift, a crucial topic for reliable monitoring of the long-term gravity variations in active volcanic areas. In fact, a challenge in time-lapse gravimetry is the proper separation of the instrumental variations from real gravity changes eventually attributable to recharge or drainage processes of magma or fluids in the feeding systems of active volcanoes. A negative finding coming out from the intercomparison is that, even when applying the tilt correction, the gravimetric residuals obtained with the gPh#116 are an order of magnitude larger and quite inconsistent with those obtained with co-located superconducting gravimeters. We guess this problem could be overcome by installing the gravimeter on an auto-levelling platform. From the analysis of the gravity records, a reliable tidal gravity model was derived, which we believe will help to improve the accuracy of volcano monitoring, as it will allow appropriate correction of tidal effects for both relative and absolute gravity measurements acquired in the area. Two further interesting elements arose from our study: (1) a peculiar cavity effect of the SV underground laboratory that seems to influence the tilt change; (2) the small residual gravity signals are time correlated with the rainfall peaks and are compatible with gravity decreases induced by increases in soil moisture above the gravimeter.