Deep Underground Site Research Articles

Coupled model for microbial growth and phase mass transfer in pressurized batch reactors in the context of underground hydrogen storage.

A rising interest in a strong hydrogen economy as a part of the future net-zero economy results in an increasing necessity to store hydrogen as a raw material or an energy carrier. Experience and studies show that storing hydrogen in deep underground sites could enable microbial conversion of hydrogen. To predict and examine the loss of hydrogen, laboratory studies, and analysis are essential. A growth model is required to interpret batch or chemostat experiments. With this model, the parameters of microbial growth, and the conversion of hydrogen can be specified. This study presents experiments with methanogens and a hydrogen/carbon dioxide gas mixture performed in batch reactors. Further, the microbial growth was modeled by a double Monod model with hydrogen and carbon dioxide as the limiting substrates. As the amount of carbon dioxide dissolved in the water phase can not be neglected, both phases were considered in the proposed model. The mass-transfer rate between the gas and water phase was implemented by a linear relation including the concentrations in both phases and the mass-transfer coefficient. With the resulting coupled model, it was possible to match the pressure behavior in the reactor and conclude the microbial growth kinetics. Two types of methanogenic species were tested to validate the model. The mass transfer coefficient proves to impact the growth behavior in porous media. The mathematical model and experimental data are necessary to determine the growth rate and yield coefficient.

Outstanding stability of Gd-doped UO2 against surface oxidation: First-principles study

An accurate understanding of structural integrity and chemical reactivity of UO2 disposed in deep underground sites is of importance. Owing to the specific condition of the site location, UO2 may have substantially different properties from the conventional prediction. In this study, we demonstrate that the oxidation resistivity of UO2 is considerably modified by gadolinium (Gd), which is the element of neutron absorber and a byproduct of nuclear decay of radioactive U-235. Using density functional theory calculations, we investigate how the oxidation mechanism of UO2 changes with Gd incorporation in U lattice. Our study indicates that Gd remarkably enhances the thermodynamic stability of pristine UO2 against surface oxidation via three underlying mechanisms: (i) weakens the chemical bonding of adsorbed oxygen atom (O) with U, (ii) reduces active sites (U) for oxygen adsorption, and (iii) suppresses the subsurface diffusion of adsorbed O delaying the growth of the oxide layers on the UO2. Electronic and lattice structure analyses for Gd-doped UO2 indicate that amount of charge transfer from U to O is critically reduced and the lattice of the UO2 surface is contracted. Our results provide useful information for understanding long-term stability and improving the structural integrity of UO2 through the chemical doping process.

A large area detector for thermal neutron flux measurements at the KamLAND site

A large area (0.5 m × 0.5 m) thermal neutron detector was developed based on 0.32 mm-thick 6LiF:ZnS(Ag) scintillator sheets. The detector was constructed for measurements of seasonal variations in low intensity thermal neutron flux at deep underground sites. The detector response to neutrons was studied using a low intensity 241Am/9Be(α,n) neutron source. The digital pulse shape discrimination technique was applied to separate neutron capture events from the background caused by traces of α-emitters from Uranium and Thorium decay chains in scintillator components. The thermal neutron detection efficiency was 0.368 ± 0.018 (0.155 ± 0.009) before (after) event selection based on the digital pulse shape discrimination method. The measured α-particle background event rate in the 6LiF:ZnS(Ag) scintillator was (4.88 ± 0.06(stat))×10−6α cm−2 s−1. As a test of detector performance we measured the thermal neutron flux at the KamLAND area of the Kamioka neutrino observatory and compared it with result of the neutron flux measurement carried out at the Super-Kamiokande site. The thermal neutron flux at KamLAND was (6.43 ± 0.50)×10−6 n cm−2 s−1 that included ∼10% contribution from neutrons with energies above 1 eV. During the detector construction we identified a source of high amplitude noise pulses generated by 5-inch R1250 photomultipliers manufactured by Hamamatsu Photonics K. K.

The GINGER project and status of the GINGERino prototype at LNGS

GINGER (Gyroscopes IN GEneral Relativity) is a proposal for measuring in a ground-based laboratory the Lense-Thirring effect, known also as inertial frame dragging, that is predicted by General Relativity, and is induced by the rotation of a massive source. GINGER will consist in an array of at least three square ring lasers, mutually orthogonal, with about 6-10 m side, and located in a deep underground site, possibly the INFN - National Laboratories of Gran Sasso. The tri-axial design will provide a complete estimation of the laboratory frame angular velocity, to be compared with the Earths rotation estimate provided by IERS with respect the fixed stars frame. Large-size ring lasers have already reached a very high sensitivity, allowing for relevant geodetic measurements. The accuracy required for Lense-Thirring effect measurement is higher than 10-14 rad/s and therefore Earth angular velocity must be measured within one part in 10-9. A 3.6 m side, square ring laser, called GINGERino, has been recently installed inside the Gran Sasso underground laboratories in order to qualify the site for a future installation of GINGER. We discuss the current status of the experimental work, and in particular of the GINGERino prototype.

A 100-m Fabry–Pérot Cavity with Automatic Alignment Controls for Long-Term Observations of Earth’s Strain

We have developed and built a highly accurate laser strainmeter for geophysical observations. It features the precise length measurement of a 100-m optical cavity with reference to a stable quantum standard. Unlike conventional laser strainmeters based on simple Michelson interferometers that require uninterrupted fringe counting to track the evolution of ground deformations, this instrument is able to determine the absolute length of a cavity at any given time. The instrument offers advantage in covering a variety of geophysical events, ranging from instantaneous earthquakes to crustal deformations associated with tectonic strain changes that persist over time. An automatic alignment control and an autonomous relocking system have been developed to realize stable performance and maximize observation times. It was installed in a deep underground site at the Kamioka mine in Japan, and an effective resolution of 2 × (10−8 − 10−7) m was achieved. The regular tidal deformations and co-seismic strain changes were in good agreement with those from a theoretical model and a co-located conventional laser strainmeter. Only the new instrument was able to record large strain steps caused by a nearby large earthquake because of its capability of absolute length determination.

Modelling of carbon steel corrosion under oxygen depleted environment

In Japan, high level radioactive waste (HLW) produced by reprocessing spent fuels has been planned to be fixed in the glass solid body which is enclosed in the stainless steel canister which is further enclosed in the metal overpack. The overpacks are emplaced in tunnels at a deep underground facility. Carbon steel is the most important candidate material for the overpack, because the corrosion rate of carbon steel is known to be as low as 10 μm/year at an assumed deep underground site which is kept at oxygen depleted condition. The corrosion rate of carbon steel measured in the laboratory was found to be almost 10 μm/year at the initial stage, and decreases to a steady state corrosion rate in the order of 0·1–0·01 μm/year, changing with time according to an inverse parabolic rate law. A corrosion model assuming the diffusion of H2O molecule through the precipitated corrosion film (Fe3O4) has been developed to rationalise the observed corrosion rate law under oxygen depleted environment. In this study, an improved model which takes account of the corrosion film dissolution has been proposed by assuming that the dissolution of precipitated Fe3O4 film is controlled by mass transfer process through adjusting diffusion layer in the solution. Digital simulation based on the improved corrosion model with suitable parameters such as the diffusion constant of H2O in the corrosion film and concentration of dissolved Fe2+ species at the surface of the Fe3O4 corrosion film was found well to simulate the observed corrosion rate change with time at various pH values as a function of partial pressure of hydrogen gas and to predict a low and steady state corrosion rate after long time exposure.

The SNOLAB Deep Underground Research Facility and Its Science Program

This laboratory portrait describes the developing infrastructure and science program at the Canadian deep underground research facility, SNOLAB. Several contemporary science studies in particle and astro-particle physics, such as Galactic dark matter searches, man-made, terrestrial, solar and supernova neutrino, and neutrino-less double-beta studies, require rigorous radio-isotopic background control and deep underground science facilities, to afford shielding from penetrating cosmic rays and their secondary by-products. New threads of research focused on deep sub-surface biology, chemistry, geology, and engineering have also been developing rapidly at several deep underground sites, benefitting from the significant investment in underground access and infrastructure developed.

Microstructural based time-dependent failure mechanism and its relation to geological background

The time-dependent hydro-mechanical behavior of rocks is important in assessing the long-term stability of deep underground excavation sites meant for long-term storage of radioactive waste. While evaluating the manner in which damage growth progresses at an excavation site, it is important to represent the failure criteria and microcrack evolution from the viewpoint of factors pertaining to microcrack geometry, such as the crack density. We performed creep tests on Inada granite samples to examine the effects of water, confining pressure, and weathering on time-dependent failure. The crack density of the samples, which was damaged at three characteristic stages of creep behavior (i.e., primary, secondary, and tertiary creep), was measured by means of a longitudinal wave velocity test; the microcrack evolution and failure criteria are discussed on the basis of the crack tensor determined in the test. The following conclusions were reached from the test results. (1) The onset of tertiary creep corresponds to the peak stress under static loading conditions, and the tertiary creep stage corresponds to the post-failure region. (2) At the onset of tertiary creep, the crack density can be the failure criterion for time-dependent failure, and crack density can be estimated using the longitudinal wave velocity. (3) The time to failure for weathered granitic rock is approximately ten times faster than that for intact granitic rock. (4) The ratio of the mica group mineral in the granite may affect the time to failure, a fact that offers insight into the time-dependent stability of a rock mass on the field scale.

A possible underground accelerator in the Dresden Felsenkeller

Typical energies in an astrophysical scenario lie far below the Coulomb barrier. Therefore the cross section is tiny, and in an in-beam experiment the experimental counting rate in γ detectors is low. Often it is dominated by cosmic-ray induced background, even if suitable anticoincidence shields are applied. This problem can be overcome by placing the accelerator deep underground, where a sufficiently thick rock overburden attenuates cosmic rays. Based on the success of the LUNA 400 kV underground accelerator in Italy, several higher-energy underground accelerators are in the planning phase worldwide. All of them should be hosted in laboratories shielded by over 1000 m of rock, where cosmic-ray muons are negligible for the purposes of nuclear physics experiments. A preliminary background study indicates that a combined approach, using a shallow underground laboratory below 47 m of rock and an active shield to suppress surviving muons, results in a background level that is similar to deep underground sites.

Shallow-underground accelerator sites for nuclear astrophysics: Is the background low enough?

In order to reliably estimate the rate of a charged particle induced nuclear reaction in a non-explosive astrophysical scenario, its cross-section must be measured far below the Coulomb barrier. However, at the corresponding energies the cross-section values are very low, so that the experimental counting rate is dominated by cosmic-ray induced background, even if a suitable anticoincidence shield is applied. This problem can be overcome by performing an accelerator-based experiment in a deep underground site, as has been done with great success at the LUNA 0.4MV accelerator in Gran Sasso, Italy. Several underground accelerators with higher beam energy are in the planning phase worldwide. All of them are shielded by over 1000m of rock, a depth at which cosmic-ray effects are negligible for the purposes of nuclear astrophysics experiments. It is shown here that a combined approach, using a shallow-underground laboratory below 47m of rock and an active shield to veto surviving muons in simple detectors, results in a background level that is not far from that of deep underground sites. Data have been obtained using two “traveling” γ-detectors. They have been transported both shallow underground, to the Dresden Felsenkeller in Germany, and deep underground, to the Gran Sasso laboratory in Italy. As shallow-underground facilities are more easily accessible than deep-underground ones, the present finding holds the promise of greatly accelerated progress in the field of cross-section measurements for nuclear astrophysics.

DOE looks hard at taking over deep underground site

At stake is US leadership in the particle-physics intensity frontier.At stake is US leadership in the particle-physics intensity frontier.

Material issues for the super neutrino beam and high-intensity spallation source (measurements using the multi-particle correlation)

I discuss the technology related to producing the high-intensity spallation neutron source, and the super neutrino beam for neutrino oscillation studied at Brookhaven National Laboratory, especially material integrity. The pitting problem for solid walled liquid mercury target, has been remedied by the Kolsterized target in some what, further study for required neutron source is needed. For neutrino source study, the low mass nuclei target such as carbon–carbon composite target is promising results and the use of the tacky gluey target composed with entangled string material for high mass nuclei seems to be desirable to get high integrity stand for large energy deposition by short proton injection. Recent developments in nano-technology, such as CCD, might alleviate the high demands of maintaining the integrity of the target material. I also describe the advantages of operating the many facilities including the fast-pulsed prompt super-critical reactor in a deep underground site.

A European megaton project at Fréjus

An international facility project with a megaton-size Cerenkov as the main detector, in the Frejus Deep Underground site, is presented. The physics program, MEMPHYS, includes both non-accelerator (proton decay, atmospheric and solar neutrinos, neutrinos from supernovae, etc.) and accelerator (neutrino oscillations with super-beams and beta-beams from CERN) experiments.

A methodology for determining thermal properties of rocks

The migration of heat in porous media has attracted attention of the research fraternity, since almost a century. Studies conducted in the past reveal that heat migration in a medium primarily depends on its thermal resistivity (defined as the ability of the material to resist heat flow in it), its specific heat (defined as the ability of the material to store heat) and thermal diffusivity (which combines the transmission and storage properties of the material and is an indicative of the rate of change of temperature within the material). For safe and proper execution of various civil and electrical engineering projects, determination of thermal properties of soils such as thermal resistivity [1–22], thermal diffusivity [1,23] and specific heat [3,19] is quite essential. However, thermal properties of rocks would play an important role for extremely environmental sensitive projects such as disposal of high-level radioactive waste in deep underground disposal sites or repositories [24,25]. In this direction, attempts have been made wherein rock has been powdered to determine its thermal conductivity [26–28] or its chips have been used [29]. However, these studies would not yield accurate results, mainly, due to the lack of representative matrix of the rock mass [30]. Attempts have also been made by earlier researchers to determine thermal properties of rocks using divided bar method [31], the transient plane source, TPS-method [32], and different probe methods [33–34]. However, these methods are time consuming, expensive, and quite complicated in terms of instrumentation and insulation of the surfaces of the rock sample from the ambience. With this in view, an attempt has been made to develop a methodology, which can be employed to determine thermal properties of the rock samples easily and quickly. Details of the methodology are presented in this technical note and its validation has been demonstrated vis- a-vis results reported in the literature.

Dark matter search with a low temperature sapphire bolometer

Abstract A dark matter detection experiment using a low temperature 24 g sapphire bolometer is presented. The low radioactive background cryogenic facility, installed in a deep underground site, is described, as well as the low-noise read-out electronics and the data analysis. From the energy spectrum, measured down to 4 keV, exclusion plots are derived for WIMPs having coherent vector coupling or axial coupling to ordinary matter.

CALCULATION OF THE POWER LAW INDEX FOR A TIME SERIES BY MEANS OF ITS FRACTAL DIMENSION

The relationship between the power-law index for a time series and the fractal dimensions for both the original and the integrated time series, is investigated by using a numerical experiment. This relationship is extended and applied to the cosmic ray time series recorded at the deep underground site at Matsushiro. It is shown that we can use the present method in order to obtain the stable and reliable value of the power-law index of a time series, even if the time series has relatively large statistical fluctuations.

Underground science initiatives at Los Alamos

Recently, the Los Alamos National Laboratory has proposed two major new initiatives in underground science. Following the dissolution of the original gallium solar-neutrino collaboration, Los Alamos has formed a new North American collaboration. We briefly review the rationale for solar-neutrino research, outline the proposal and new Monte Carlo simulations, and describe the candidate locations for the experiment. Because there is no deep underground site in North America suitable for a dedicated permanent laboratory, Los Alamos has conducted a survey of possible sites and developed a proposal to create a new National Underground Science Facility. This paper also reviews that proposal.