Underground Research Facility Research Articles

Coupled flow and transport modelling of a large-scale in situ migration experiment with 14 C-labelled natural organic matter colloids in Boom Clay

Abstract Twenty-five years ago, a unique long-term and large-scale in situ experiment with 14 C-labelled natural organic matter (NOM) was set up at the HADES underground research facility in Mol (Belgium) to study its migration behaviour. Natural organic matter plays an important role in the mobility of various safety-relevant radionuclides, which is critical in the context of Safety & Performance Assessment (SA/PA) calculations for a possible nuclear waste repository. The objective of this work is to enlarge the confidence in current NOM transport models by validating them with the in situ experiment, which is still continued to this day. Stepwise adding more complexity to the model resulted in a 10-parameter model with which excellent fits to the data are obtained. The model considers two different fractions that are transported by advection and diffusion and can be subject to both irreversible and reversible immobilization processes. The associated fitted parameter values compare well with values determined on small-scale migration experiments. This builds confidence in the NOM transport model, which in turn contributes to the confidence in the outcome of the radionuclide migration calculations performed in the context of SA/PA. These results again highlight the incredible value of such long-running experiments at underground research facilities like HADES.

A New Digital Analysis Technique for the Mechanical Aperture and Contact Area of Rock Fractures

In this study, a new digital technique for the analysis of the mechanical aperture and contact area of rock fractures under various normal stresses is proposed. The technique requires point cloud data of the upper and lower fracture surfaces, pressure film image data of the fracture, and normal deformation data of the fracture as input data. Three steps of algorithms were constructed using these input data: (1) a primary matching algorithm that considers the shape of the fracture surfaces; (2) a secondary matching algorithm that uses pressure film images; and (3) a translation algorithm that considers the normal deformation of a fracture. The applicability of the proposed technique was investigated using natural fracture specimens sampled at an underground research facility in Korea. In this process, the technique was validated through a comparison with the empirical equation suggested in a previous study. The proposed technique has the advantage of being able to analyze changes in the mechanical aperture and contact area under various normal stresses without multiple experiments. In addition, the change in the contact area on the fracture surface according to the normal stress can be analyzed in detail.

Characterization of Boom Clay anisotropic THM behaviour based on two heating tests at different scales in the HADES URL

Abstract To examine the impact of the heat generated by high-level radioactive waste on Boom Clay, two heater tests have been launched in the HADES underground research facility: the small-scale ATLAS Heater Test and the large-scale PRACLAY Heater Test. The major objective of these tests is to confirm and refine the thermo-hydro-mechanical (THM) constitutive models and associated parameter values obtained from a laboratory characterization programme. This paper presents the observations from the ATLAS and PRACLAY heater tests and the combined numerical modelling of these tests. To characterize the excavation damaged zone in the clay around these tests, a mechanical model with a strain-dependent elastic modulus is introduced for the Boom Clay. The consistency between the observations from laboratory tests and in-situ tests and the outcomes from the numerical models strengthen the confidence in our understanding of the THM behaviour of Boom Clay. They also enabled us to validate the mechanical model and produce a set of anisotropic THM property values for both intact and damaged Boom Clay.

Geo- and reactor antineutrino sensitivity at THEIA

We present the sensitivity of the Theia experiment to low-energy geo- and reactor antineutrinos. For this study, we consider one of the possible proposed designs, a 17.8-ktonne fiducial volume Theia-25 detector filled with water-based liquid scintillator placed at Sanford Underground Research Facility (SURF). We demonstrate Theia’s sensitivity to measure the geo- and reactor antineutrinos via inverse-beta decay interactions after one year of data taking with 11.9 times 10^{32} free target protons. Considering all uncertainties on input throughout the whole analysis chain, the expected number of geo- and reactor antineutrinos is 220,^{+30}_{-24} (stats+syst) and 168,^{+26}_{-24} (stat+sys), respectively, after one year of data taking. The corresponding expected fit precision of a sole experiment is evaluated at 8.7% and 10.1%, respectively. We also demonstrate the sensitivity towards fitting individual Th and U contributions, with best fit values of N_text {Th}=40^{+26}_{-22} (stat+sys) and N_text {U}=180^{+30}_{-24} (stat+sys). Finally, from the fit results of individual Th and U contributions, we evaluate the mantle signal to be S_text {mantle} = 9.3,pm [5.2,5.4] NIU (stat+sys). This was obtained assuming a full-range positive correlation (rho _cin [0, 1]) between Th and U, and the projected uncertainties on the crust contributions of 8.3% (Th) and 7.0% (U).

Fracture toughness of schist, amphibolite, and rhyolite from the Sanford Underground Research Facility (SURF), Lead, South Dakota

The Cracked Chevron Notched Brazilian Disc (CCNBD) method was selected for Mode I fracture toughness tests on Poorman schist, Yates amphibolite, and rhyolite dikes from the EGS Collab site at the SURF in Lead, South Dakota. The effects of lithology, anisotropy, and loading rate were investigated. Fracture toughness was greatest in amphibolite, with schist and rhyolite having similar toughness values ({K}_{amphibolite} > {K}_{rhyolite} ≈ {K}_{schist}). The effects of anisotropy on fracture toughness were investigated in the foliated schist samples. Schist samples were prepared in three geometries (divider, arrester, and short transverse) which controlled how the fracture would propagate relative to foliations. The divider geometry was strongest and short transverse geometry was the weakest ({K}_{divider} > {K}_{arrester} > {K}_{short transverse}). Fracture toughness was observed to decrease with decreasing loading rate. Optical and SEM microscopy revealed that for the short transverse geometry, fractures tended to propagate along grain boundaries, whereas in arrester and divider geometries fractures tended to propagate through grains. In foliated samples, the tortuosity of the fracture observed in thin section was greater in arrester and divider geometries than in short transverse geometries.

The potential for bacteria from carbon-limited deep terrestrial environments to participate in chlorine cycling.

Bacteria capable of dehalogenation via reductive or hydrolytic pathways are ubiquitous. Little is known, however, about the prevalence of bacterial dechlorination in deep terrestrial environments with a limited carbon supply. In this study we analyzed published genomes from three deep terrestrial subsurface sites: a deep aquifer in Western Siberia, the Sanford Underground Research Facility in South Dakota, USA, and the Soudan Underground Iron Mine (SUIM) in Minnesota, USA to determine if there was evidence to suggest that microbial dehalogenation was possible in these environments. Diverse dehalogenase genes were present in all analyzed metagenomes, with reductive dehalogenase and haloalkane dehalogenase genes the most common. Taxonomic analysis of both hydrolytic and reductive dehalogenase genes was performed to explore their affiliation; this analysis indicated that at the SUIM site, hydrolytic dehalogenase genes were taxonomically affiliated with Marinobacter species. Because of this affiliation, experiments were also performed with Marinobacter subterrani strain JG233 ('JG233'), an organism containing three predicted hydrolytic dehalogenase genes and isolated from the SUIM site, to determine whether hydrolytic dehalogenation was an active process and involved in growth on a chlorocarboxylic acid. Presence of these genes in genome appears to be functional, as JG233 was capable of chloroacetate dechlorination with simultaneous chloride release. Stable isotope experiments combined with confocal Raman microspectroscopy demonstrated that JG233 incorporated carbon from 13C-chloroacetate into its biomass. These experiments suggest that organisms present in these extreme and often low-carbon environments are capable of reductive and hydrolytic dechlorination and, based on laboratory experiments, may use this capability as a competitive advantage by utilizing chlorinated organic compounds for growth, either directly or after dechlorination.

Overview and status of the Long-Baseline Neutrino Facility Far Site cryogenics system

The Sanford Underground Research Facility (SURF) will host the Far Detector of the Deep Underground Neutrino Experiment (DUNE), an international multi-kiloton Long-Baseline neutrino experiment that will be installed about one and a half kilometers underground in Lead, SD. Detectors will be located inside four cryostats filled with almost 70,000 metric tons of ultrapure liquid argon, with a level of impurities lower than 100 parts per trillion of oxygen equivalent contamination. The cryogenics infrastructure supporting this experiment is provided by the Long-Baseline Neutrino Facility (LBNF). This contribution presents modes of operation, layout, and main features of the LBNF Far Site cryogenic system, which is composed of three subsystems: Infrastructure, Proximity, and Internal cryogenics. The Infrastructure cryogenics supports the needs of the cryostat and Proximity cryogenics. It includes the equipment to receive the argon in liquid phase, vaporize it and transfer it underground as a gas, the nitrogen system (composed of the refrigeration system, liquid nitrogen buffer tanks and liquid and gaseous nitrogen distribution), liquid and gaseous argon distribution and process controls. The Proximity cryogenics receives fluids from the Infrastructure cryogenics and delivers them to the Internal cryogenics at the required temperature, pressure, purity and mass flow rate. It includes the argon condensers, liquid and gaseous argon purification and regeneration systems, nitrogen and argon phase separators, piping, valves, and instrumentation. The Internal cryogenics comprises the liquid and gaseous argon distribution inside the cryostats for the commissioning, cool down, fill, and steady state operations of the cryostats and detectors. An international engineering team is designing these systems and will manufacture, install, commission, and qualify them. This contribution describes the main features, performance, functional requirements, and modes of operation of the LBNF Far Site cryogenics system. It also presents the status of the design, along with present and future needs to support the DUNE experiment.

Measurement of Low-Energy Resonance Strengths in the O18(α,γ)Ne22 Reaction

The ^{18}O(α,γ)^{22}Ne reaction is an essential part of a reaction chain that produces the ^{22}Ne(α,n)^{25}Mg neutron source for both the weak and main components of the slow neutron-capture process. At temperatures of stellar helium burning, the astrophysically relevant resonances in the ^{18}O(α,γ)^{22}Ne reaction that dominate the reaction rate occur at α particle energies E_{lab} of 472 and 569 keV. However, previous experiments have shown the strengths of these two resonances to be very weak, and only upper limits or partial resonance strengths could be obtained. This Letter reports the first direct measurement of the total resonance strength for the 472- and 569-keV resonances, 0.26±0.05 and 0.63±0.30 μeV, respectively. New resonance strengths for the resonances at α particle energies of 662.1, 749.9, and 767.6 keV are also provided. These results were achieved in an experiment optimized for background suppression and detection efficiency. The experiment was performed at the Sanford Underground Research Facility, in the 4850-foot underground cavity dedicated to the Compact Accelerator System for Performing Astrophysical Research. The experimental end station used the γ-summing High EffiCiency TOtal absorption spectrometeR. Compared to previous works, the results decrease the stellar reaction rate by as much as ≈46_{-11}^{+6}% in the relevant temperature range of stellar helium burning.

Unsupervised learning from three-component accelerometer data to monitor the spatiotemporal evolution of meso-scale hydraulic fractures

Abstract Enhanced geothermal systems can provide a substantial share of the global energy demand. There exist several hurdles in the engineering implementations of such geothermal systems. One such hurdle is the accurate monitoring of the fracture networks created in subsurface through hydraulic stimulation of these systems. Micro seismicity associated with the stimulation is the primary means to locate the event hypocenters for estimating the stimulated rock volume. Existing methods for location the hypocenters are restricted to only the highest amplitude impulsive signals that are simultaneously detected on several sensors. Consequently, a large portion (usually ∼99%) of the measurements are left unused. In this paper, an unsupervised manifold-approximation followed by clustering of 3-component accelerometer data is used to analyze the seismicity recorded on a monitoring well. With this method, a larger portion of the measured signal is used for the monitoring of the hydraulic fracture network. We analyze the EGS Collab experiment 1 microseismic data, recorded at the Sanford Underground Research Facility, South Dakota. Using the data from a single three-component accelerometer, the polarization features viz. Azimuth, incidence, rectilinearity, and planarity are used as inputs for the unsupervised manifold approximation followed by clustering. Our study shows that density-based clusters in the projected 3D space correspond to distinct types of hydraulically fractured zones around the injection point. We show that the temporal evolution of these clusters can be used to track fracture creation and propagation.

Multi-disciplinary characterizations of the BedrettoLab – a new underground geoscience research facility

Abstract. The increased interest in subsurface development (e.g., unconventional hydrocarbon, engineered geothermal systems (EGSs), waste disposal) and the associated (triggered or induced) seismicity calls for a better understanding of the hydro-seismo-mechanical coupling in fractured rock masses. Being able to bridge the knowledge gap between laboratory and reservoir scales, controllable meso-scale in situ experiments are deemed indispensable. In an effort to access and instrument rock masses of hectometer size, the Bedretto Underground Laboratory for Geosciences and Geoenergies (“BedrettoLab”) was established in 2018 in the existing Bedretto Tunnel (Ticino, Switzerland), with an average overburden of 1000 m. In this paper, we introduce the BedrettoLab, its general setting and current status. Combined geological, geomechanical and geophysical methods were employed in a hectometer-scale rock mass explored by several boreholes to characterize the in situ conditions and internal structures of the rock volume. The rock volume features three distinct units, with the middle fault zone sandwiched by two relatively intact units. The middle fault zone unit appears to be a representative feature of the site, as similar structures repeat every several hundreds of meters along the tunnel. The lithological variations across the characterization boreholes manifest the complexity and heterogeneity of the rock volume and are accompanied by compartmentalized hydrostructures and significant stress rotations. With this complexity, the characterized rock volume is considered characteristic of the heterogeneity that is typically encountered in subsurface exploration and development. The BedrettoLab can adequately serve as a test-bed that allows for in-depth study of the hydro-seismo-mechanical response of fractured crystalline rock masses.

Hydro‐Mechanical Measurements of Sheared Crystalline Rock Fractures With Applications for EGS Collab Experiments 1 and 2

AbstractWe present hydro‐mechanical measurements that characterize shear on natural fractures in schist, amphibolite, and rhyolite specimens from the enhanced geothermal system (EGS) Collab Project's Experiment 1 and 2 sites (E1 and E2) at the Sanford Underground Research Facility. We employed a triaxial direct shear method augmented with X‐ray imaging to perform hydroshearing (injection‐induced shearing) and mechanical shearing on naturally fractured specimens at in situ stress conditions. Measurements included fracture permeability, strength, stress‐dependent aperture, shear dilation, and frictional strength. Results reveal that in situ natural fractures must be permeable, weak, and shear‐oriented to be hydrosheared, and only a subset of the observable in situ fractures were suitable. When sheared, the fracture permeability typically increased by a factor of 10 or more and this increase was retained over time. However, shear slip did not always result in permeability increase. High phyllosilicate content associated with exceptionally weak fractures exhibited poor or even decreased permeability after stimulation. These measurements in combination with site data were used to conduct a slip‐tendency analysis for different fracture sets, and we selected the top candidate natural fractures for hydroshearing at the EGS Collab sites. We also found that the lower in situ shear stress and stronger fractures at the E2 site make hydroshearing more challenging than at the E1 site. Overall, the methods and analysis used in our work can be applied to any geothermal project to identify in situ joint sets that are best suited for hydroshearing, which in turn can help to optimize well placement and energy production.

О возможных проявлениях горных ударов при сооружении ПИЛ и методах их предотвращения

At great depths, the Yeniseiskiy section of the Nizhnekanskiy rock mass selected for the construction of an underground research facility (URF) may involve some areas of firm rocks with high internal stresses that may cause spontaneous rock bursts. The paper provides a qualitative description of the mechanism standing behind the rock burst process, the necessary and sufficient conditions for its occurrence and the conditions for its extinction. It considers some engineering methods dealing with rock bursts which may be applied given special requirements set out for the URF construction.

Подземная исследовательская лаборатория: результаты 12-летних наблюдений за современными движениями земной коры средствами ГНСС

The paper considers geodetic observations focused on modern earth crust movements and rates of its deformations carried out over the period from 2010 to 2022 in the siting area of an underground research facility (URF) in the Nizhnekanskiy rock mass and summarizes their findings. The study demonstrates that the developed GNSS observation method can be used to measure the velocities of modern horizontal movements with a high accuracy at the level of 2.4 mm. It also presents a structural-kinematic model of block movements and deformations, including the spatial layout of areas with maximum velocities of compressive and tensile deformations. The highest rates of horizontal movements were identified in the dynamic influence zone of the Muratov and Pravoberezhniy faults. In general, GNSS observations have shown that the region could be considered geodynamically stable, the maximum strain rates did not exceed 5·10–7 per year. The study also evidences the cyclic nature of the evolving modern movements, which significantly complicates the adoption of a final conclusion on the geodynamic activity of the URF siting region.

Design, construction and operation of the ProtoDUNE-SP Liquid Argon TPC

The ProtoDUNE-SP detector is a single-phase liquid argon time projection chamber (LArTPC) that was constructed and operated in the CERN North Area at the end of the H4 beamline. This detector is a prototype for the first far detector module of the Deep Underground Neutrino Experiment (DUNE), which will be constructed at the Sandford Underground Research Facility (SURF) in Lead, South Dakota, U.S.A. The ProtoDUNE-SP detector incorporates full-size components as designed for DUNE and has an active volume of 7 × 6 × 7.2 m3. The H4 beam delivers incident particles with well-measured momenta and high-purity particle identification. ProtoDUNE-SP's successful operation between 2018 and 2020 demonstrates the effectiveness of the single-phase far detector design. This paper describes the design, construction, assembly and operation of the detector components.

Projected sensitivity of the LUX-ZEPLIN experiment to the two-neutrino and neutrinoless double β decays of Xe134

The projected sensitivity of the LUX-ZEPLIN (LZ) experiment to two-neutrino and neutrinoless double β decay of Xe134 is presented. LZ is a 10-tonne xenon time-projection chamber optimized for the detection of dark matter particles and is expected to start operating in 2021 at Sanford Underground Research Facility, USA. Its large mass of natural xenon provides an exceptional opportunity to search for the double β decay of Xe134, for which xenon detectors enriched in Xe136 are less effective. For the two-neutrino decay mode, LZ is predicted to exclude values of the half-life up to 1.7×1024 years at 90% confidence level (CL) and has a three-sigma observation potential of 8.7×1023 years, approaching the predictions of nuclear models. For the neutrinoless decay mode LZ, is projected to exclude values of the half-life up to 7.3×1024 years at 90% CL.Received 19 May 2021Accepted 19 November 2021DOI:https://doi.org/10.1103/PhysRevC.104.065501©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDouble beta decayNeutrinoless double beta decayProperties90 ≤ A ≤ 149TechniquesSpectrometers & spectroscopic techniquesNuclear PhysicsParticles & Fields

DUNE Physics Program and Status

The Deep Underground Neutrino Experiment (DUNE) is a next-generation long-baseline neutrino experiment with a 70-kt liquid argon detector at the Sanford Underground Research Facility (SURF) 1300 km from Fermilab. This programme includes studies of neutrino oscillations with a high-intensity muon-neutrino beam from Fermilab; as well as, proton decay and supernova neutrino burst searches. DUNE will resolve the neutrino mass hierarchy to a precision of 5σ, for all δCP values, after 2 years of running with the nominal detector design and beam configuration. It has the potential to observe charge-parity violation in the neutrino sector to a precision of 3σ (5σ) after an exposure of 5 (10) years, for 50% of all δCP values. The status and schedule of the project is also presented.

The Sanford Underground Research Facility

The Sanford Underground Research Facility (SURF) has been operating since 2007 supporting underground research in rare-process physics, as well as offering research opportunities in other disciplines. SURF laboratory facilities include a Surface Campus as well as campuses at the 4850-foot level (1500 m, 4300 m.w.e.) that host a range of significant physics experiments, including the LUX-ZEPLIN (LZ) dark matter experiment and the MAJORANA DEMONSTRATOR neutrinoless double-beta decay experiment. The CASPAR nuclear astrophysics accelerator recently completed the first phase of operation. Furthermore, the BHUC laboratory dedicated to critical material assays for current and future experiments has been operating since Fall 2015. Construction is underway for the Long-Baseline Neutrino Facility (LBNF) that will host the international Deep Underground Neutrino Experiment (DUNE). SURF is a dedicated research facility with significant expansion capability, and applications from new experiments are welcome.

Modelling of sensitivity of underground space stability to the in situ stress uncertainties: case study at the Bukov underground research facility phase II (Rozna mine, Czechia)

Numerical modelling has been widely used in the underground excavation design, where the in situ stress state plays a crucial role in the stability analysis. However, determination of an exact stress state for a specific geological region remains uncertain due to the complicated tectonic nature and measurement limitations. The stability is thus better analysed by considering the in situ stress as a finite spectrum and pinpointing the possible worst-case scenario. The most probable scenarios of in situ stress states in the Rožná mine area were analysed based on the varying trends in principal stress ratio and mean stress values obtained from four different measurement/analysis campaigns. The influence of different in situ stress judgement on the deformation and failure characteristics of the Bukov Underground Research Facility (URF) (Phase II, Czech) were investigated by the finite volume program FLAC3D. Results show that the increased horizontal stress anisotropy and the mean stress level jointly increase the overall deformation and lower the URF stability. Such influences on the roadway horizontal convergence are more considerable than the vertical ones. A mathematical model considering mean stress and horizontal stress ratio was proposed to quantitatively describe the overall stability, especially useful for excavations possessing complicated configuration.

Molecular-Level Speciation of Eu(III) Adsorbed on a Migmatized Gneiss As Determined Using μTRLFS.

The interaction of Eu(III) with thin sections of migmatized gneiss from the Bukov Underground Research Facility (URF), Czech Republic, was characterized by microfocus time-resolved laser-induced luminescence spectroscopy (μTRLFS) with a spatial resolution of ∼20 μm, well below typical grain sizes of the material. By this approach, sorption processes can be characterized on the molecular level while maintaining the relationship of the speciation with mineralogy and topography. The sample mineralogy was characterized by powder X-ray diffraction and Raman microscopy, and the sorption was independently quantified by autoradiography using 152Eu. Representative μTRLFS studies over large areas of multiple mm2 reveal that sorption on the heterogeneous material is not dominated by any of the typical major constituent minerals (quartz, feldspar, and mica). Instead, minor phases such as chlorite and prehnite control the Eu(III) distribution, despite their low contribution to the overall composition of the material, as well as common but less studied phases like Mg-hornblende. In particular, prehnite shows high a sorption uptake as well as strong binding of Eu to the mineral surface. Sorption on prehnite and hornblende happens at the expense of feldspar, which showed the highest sorption uptake in a previous spatially resolved study on granitic rock. Similarly, sorption on quartz is reduced, even though only low quantities of strongly bound Eu(III) were found here previously. Our results illustrate how competition of mineral surfaces for adsorbing cations drives the metal distribution in heterogeneous systems.

In Situ Continuous Monitoring of Borehole Displacements Induced by Stimulated Hydrofracture Growth

AbstractWe provide direct observations of the three‐dimensional displacements of a fluid‐driven fracture during water injections in a borehole at ∼1.5 km depth in the crystalline rock at the Sanford Underground Research Facility (USA). Micro‐shearing of the borehole initiates on a foliation plane at 61% of the minimum principal stress σ3. As the fluid pressure increases further up to 112% of σ3, borehole axial and radial displacements increase with injection time highlighting the opening and sliding of a new hydrofracture growing ∼10 m away from the borehole, in accordance with the ambient normal stress regime and in alignment with the microseismicity. Our study reveals how important it is to consider monitoring zonal deformation in conjunction with pressure and flow to better manage the complex hydromechanical evolution of the growing fracture.