Horonobe Underground Research Laboratory Research Articles

Potential for microbial H2 and metal transformations associated with novel bacteria and archaea in deep terrestrial subsurface sediments

Geological sequestration in deep underground repositories is the prevailing proposed route for radioactive waste disposal. After the disposal of radioactive waste in the subsurface, H2 may be produced by corrosion of steel and, ultimately, radionuclides will be exposed to the surrounding environment. To evaluate the potential for microbial activities to impact disposal systems, we explored the microbial community structure and metabolic functions of a sediment-hosted ecosystem at the Horonobe Underground Research Laboratory, Hokkaido, Japan. Overall, we found that the ecosystem hosted organisms from diverse lineages, including many from the phyla that lack isolated representatives. The majority of organisms can metabolize H2, often via oxidative [NiFe] hydrogenases or electron-bifurcating [FeFe] hydrogenases that enable ferredoxin-based pathways, including the ion motive Rnf complex. Many organisms implicated in H2 metabolism are also predicted to catalyze carbon, nitrogen, iron and sulfur transformations. Notably, iron-based metabolism is predicted in a novel lineage of Actinobacteria and in a putative methane-oxidizing ANME-2d archaeon. We infer an ecological model that links microorganisms to sediment-derived resources and predict potential impacts of microbial activity on H2 consumption and retardation of radionuclide migration.

Determination of dissolved natural thorium and uranium in Horonobe and Mizunami Underground Research Laboratory groundwater and its thermodynamic analysis

ABSTRACTAt two underground research laboratories situated at Horonobe and Mizunami, Japan, trace amounts of natural thorium and uranium dissolved in deep groundwater were investigated with the help of chemical pre-concentration method. The groundwater was sampled from underground boreholes under the geochemical condition of no atmospheric exposure, and the colloid contribution was checked by in situ two size-fractionated ultrafiltration systems. A rough decrease by half in the concentration after in situ filtration suggested the presence of natural colloids and suspended matter that were carriers of a portion of the elements. The Th and U concentrations in groundwater after 10 kDa filtration was evaluated as dissolved species, and was identified thermodynamically using existing hydrogeological and geochemical data, such as the mineral components in the groundwater at a given pH, ionic strength, concentration of co-existing ions, redox potential, and a hypothetical solubility-limiting solid phase. The crystalline solid phase of tetravalent thorium and uranium dioxides made the solubility very low compared with that of the amorphous phase.

Fracture Characterization and Rock Mass Damage Induced by Different Excavation Methods in the Horonobe URL of Japan

We conducted detailed fracture mapping of the soft sedimentary rocks (uniaxial compressive strength of 10–20 MPa) in shaft walls at the Horonobe Underground Research Laboratory to characterize fractures and to understand the influence of different excavation methods on rock mass damage. The mapping indicates that the fractures are numerous and can be divided into shear fractures and extension fractures. On the basis of orientation and frequency, the shear fractures are inferred to be pre-existing fractures, and the extension fractures are considered to be newly formed fractures (EDZ fractures) induced by the shaft excavation. The frequencies of pre-existing and newly formed fractures have a negative correlation, and we infer that stress relief leads to the formation of excavation damaged zone by the generation of the newly formed fractures in the parts of shaft that have intact rock, and by the reactivation of pre-existing fractures where such fractures are numerous. Although more newly formed fractures are formed by blasting excavation than by mechanical excavation, there is little difference in the comparative excavation rates. These results indicate that rock mass damage is caused by the mode of excavation rather than excavation rate. Therefore, the mechanical excavation is preferred to blasting excavation from the viewpoint of minimizing rock mass damage.

幌延深地層研究センターの350 m 調査坑道における掘削損傷領域の破壊様式の検討

幌延深地層研究センターの350 m 調査坑道における掘削損傷領域の破壊様式の検討

Interaction of rare earth elements and components of the Horonobe deep groundwater

To better understand the migration behavior of minor actinides in deep groundwater, the interactions between doped rare earth elements (REEs) and components of Horonobe deep groundwater were investigated. Approximately 10 ppb of the REEs, i.e. Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm, and Yb were doped into a groundwater sample collected from a packed section in a borehole drilled at 140 m depth in the experiment drift of Horonobe Underground Research Laboratory in Hokkaido, Japan. The groundwater sample was sequentially filtered with a 0.2 μm pore filter, and 10 kDa, 3 kDa and 1 kDa nominal molecular weight limit (NMWL) ultrafilters with conditions kept inert. Next, the filtrate solutions were analyzed with inductively coupled plasma mass spectrometry (ICP-MS) to determine the concentrations of the REEs retained in solution at each filtration step, while the used filters were analyzed through neutron activation analysis (NAA) and TOF-SIMS element mapping to determine the amounts and chemical species of the trapped fractions of REEs on each filter. A strong relationship between the ratios of REEs retained in the filtrate solutions and the ionic radii of the associated REEs was observed; i.e. smaller REEs occur in larger proportions dissolved in the solution phase under the conditions of the Horonobe groundwater. The NAA and TOF-SIMS analyses revealed that portions of the REEs were trapped by the 0.2 μm pore filter as REE phosphates, which correspond to the species predicted to be predominant by chemical equilibrium calculations for the conditions of the Horonobe groundwater. Additionally, small portions of colloidal REEs were trapped by the 10 kDa and 3 kDa NMWL ultrafilters. These results suggest that phosphate anions play an important role in the chemical behavior of REEs in saline (seawater-based) groundwater, which may be useful for predicting the migration behavior of trivalent actinides released from radioactive waste repositories in the far future.

Relationship Between Faults Oriented Parallel and Oblique to Bedding in Neogene Massive Siliceous Mudstones at The Horonobe Underground Research Laboratory, Japan

This study investigates the mechanical relationship between bedding-parallel and bedding-oblique faults in a Neogene massive siliceous mudstone at the site of the Horonobe Underground Research Laboratory (URL) in Hokkaido, Japan, on the basis of observations of drill-core recovered from pilot boreholes and fracture mapping on shaft and gallery walls. Four bedding-parallel faults with visible fault gouge, named respectively the MM Fault, the Last MM Fault, the S1 Fault, and the S2 Fault (stratigraphically, from the highest to the lowest), were observed in two pilot boreholes (PB-V01 and SAB-1). The distribution of the bedding-parallel faults at 350 m depth in the Horonobe URL indicates that these faults are spread over at least several tens of meters in parallel along a bedding plane. The observation that the bedding-oblique fault displaces the Last MM fault is consistent with the previous interpretation that the bedding- oblique faults formed after the bedding-parallel faults. In addition, the bedding-parallel faults terminate near the MM and S1 faults, indicating that the bedding-parallel faults with visible fault gouge act to terminate the propagation of younger bedding-oblique faults. In particular, the MM and S1 faults, which have a relatively thick fault gouge, appear to have had a stronger control on the propagation of bedding-oblique faults than did the Last MM fault, which has a relatively thin fault gouge.

Elastically-homogeneous lattice models of damage in geomaterials

This study involves the development of the auxiliary stress approach for producing elastically-homogeneous lattice models of damage in geomaterials. The lattice models are based on random, three-dimensional assemblages of rigid-body-spring elements. Unlike conventional lattice or particle models, the elastic constants of a material (e.g., Young’s modulus and Poisson’s ratio) are represented properly in both global and local senses, without any need for calibration. The proposed approach is demonstrated and validated through analyses of homogeneous and heterogeneous systems under uni- and tri-axial loading conditions. Comparisons are made with analytical solutions and finite element results. Thereafter, the model is used to simulate a series of standard laboratory tests: (a) split-cylinder tests, and (b) uniaxial compressive tests of sedimentary rocks at the Horonobe Underground Research Laboratory in Hokkaido, Japan. Model inputs are based on physical quantities measured in the experiments. The simulation results agree well with the experimental results in terms of pre-peak stress-strain/displacement responses, strength measurements, and failure patterns.

幌延URLにおける低アルカリ性セメント系材料の適用性確認

幌延URLにおける低アルカリ性セメント系材料の適用性確認

Influence of different excavation methods on rock mass damage in the Horonobe Underground Research Laboratory

Influence of different excavation methods on rock mass damage in the Horonobe Underground Research Laboratory

Structural Alteration of Humic Acids by Pseudomonas spp. from Deep Terrestrial Subsurface Diatomite Formations in Northernmost Japan

Bacterial utilization of humic acids (HAs) was examined under aerobic conditions using Pseudomonas spp. from diatomite from a depth of 250 m below ground level in the Horonobe Underground Research Laboratory. HA decolorization and bacterial aggregation were observed during cultivation when an auxiliary carbon source was added. High-performance size-exclusion chromatography showed that high-molecular-weight HAs were produced. Fourier transform infrared spectroscopy indicated that carboxyl groups and polysaccharide-related substances in HAs were eliminated, while aliphatic structural units and amide groups were added to HAs. These results suggested that Pseudomonas spp. utilize and alter the molecular structure of HAs under aerobic conditions caused by the construction of underground facilities.

Seven-year history of vertical Hydraulic diffusivity related to excavation around an underground facility

Significant amounts of groundwater drain induced by the excavation of an underground facility will influence various site formation parameters such as permeability. In this study, a spectral analysis was applied to long-term records of pore-pressure responses to atmospheric loading in order to clarify the history of rock permeability changes at the Horonobe Underground Research Laboratory (URL) in Japan. This study revealed that excavation of the URL influenced nearby aquifers and reduced their vertical hydraulic diffusivity. At a point approximately 130m distant from the URL, it was found that hydraulic diffusivity has decreased by approximately 7 to 55% in the five years since the excavation started. At a point approximately 860m distant from the URL, the vertical hydraulic diffusivity was found to have decreased by approximately 26%, even though pore pressure had not changed significantly. This study confirmed that long-term permeability changes could be monitored via pore and atmospheric pressure records. More specifically, during the development of a geological disposal system, which can take several tens of years, the vertical permeability of the site can be continuously monitored from the period before the start of the excavation through to the repository׳s post-closure period.

The effect of alkaline alteration on sorption properties of sedimentary rock

ABSTRACTThe potential effect of high pH plume caused by cementitious materials must be evaluated in the performance assessment for HLW geological disposal. Alkaline plume would lead to change sorption properties of host rock by primary mineral dissolution, secondary mineral precipitation and sequential change of pore water chemistry. In this study, the effect of alkaline alteration on sorption of Cs, Ni and Th was investigated using rock samples from the Horonobe Underground Research Laboratory. Crushed rock samples were reacted in high pH alkaline solution at 90°C for 45 days, 95 days and 1,383 days, respectively. As a result of sample analysis, it was supposed that zeolitic mineral was precipitated as secondary mineral. The cation exchange capacity slightly increased in comparison with the unaltered sample. Distribution coefficients (Kd) of Cs, Ni and Th on unaltered and altered rock sample were measured by batch sorption experiment in synthetic groundwater. Kdof Cs increased with the alteration period. These results show that secondary minerals contribute to the increase in Cs sorption. By contrast, Kdof Ni and Th decreased with the alteration period. This change might be caused by dissolution of clay minerals and amorphous silicates controlling Ni and Th sorption by surface complexation. These results imply that effects of alkaline alteration on Kdof rocks depend on the dissolution/precipitation of minerals, their surface properties and sorption mechanisms.

Influence of fracture orientation on excavatability of soft sedimentary rock using a hydraulic impact hammer: A case study in the Horonobe Underground Research Laboratory

In the Japanese deep geological disposal project for high-level radioactive waste, the ease of excavation of a potential host rock is a key issue for the economics of project implementation. This is because it is estimated that about 300-km of disposal drifts will need to be excavated for the disposal of 40,000 waste packages deep underground. In this study, the influence not only of the mechanical properties of intact host rock, but also fracture characteristics and their effect on the practical excavation rate of drifts using a hydraulic impact hammer were analyzed. The drifts were excavated through soft sedimentary rock in the Horonobe Underground Research Laboratory. Fracture mapping was conducted at the excavation face before every excavation round for the evaluation of fracture characteristics. Equotip hardness testing was also conducted to estimate the strength of intact rock. The results indicate that the excavation rate of the drift excavated in the direction perpendicular to natural fractures was faster than the excavation of the drift excavated in the direction parallel to natural fractures. In addition, the drift excavated in the direction perpendicular to natural fractures had a good correlation with fracture density. This result suggests that the preferred direction of disposal drifts should be perpendicular to the major natural fractures in the host rock to optimize excavatability in any deep geological disposal project.

幌延URLにおける人工バリアの性能確認試験 (1)試験計画の全体概要

幌延URLにおける人工バリアの性能確認試験 (1)試験計画の全体概要

幌延URLにおける人工バリアの性能確認試験:(3)堆積岩の掘削ズリを用いた坑道の埋め戻し材の膨潤圧特性に関する検討

幌延URLにおける人工バリアの性能確認試験:(3)堆積岩の掘削ズリを用いた坑道の埋め戻し材の膨潤圧特性に関する検討

Mine-by Experiment in a deep shaft in Neogene sedimentary rocks at Horonobe, Japan

The Japan Atomic Energy Agency (JAEA) has been implementing several research studies at the Horonobe Underground Research Laboratory (URL) in support of the Japanese R&D program for the geological disposal of High-Level Radioactive Waste (HLW). Understanding the development and properties of an EDZ (excavation disturbed or damaged zone), including the rock mechanical, hydrogeological and geochemical responses around excavated openings, is important to the design of plugs and sealing material and for performance assessment of geological disposal. The Mine-by Experiment described in this paper was carried out to investigate the development of an EDZ in one of the deep vertical shafts excavated in Neogene sedimentary rocks at the Horonobe URL site. The objective of this study is to obtain fundamental parameters of an EDZ in Neogene sedimentary rock, where case studies are few, in support of the geological disposal studies in Japan. Before and after shaft sinking, BTV (borehole television), borehole expansion tests, permeability tests and seismic velocity logging were carried out to determine initial conditions and changes in the mechanical and hydraulic properties. During shaft sinking, extensometers were installed in the rock mass to determine rock mass response to excavation. The variation of hydraulic properties was largest within one meter of the shaft wall and the variation in hydraulic conductivity was in the range of one order of magnitude.

Development of a multi-interval displacement sensor using Fiber Bragg Grating technology

We have developed a multi-interval displacement sensor using Fiber Bragg Grating (FBG) technology, which has potential for the long-term durability, high accuracy and ability to transmit data over long distances. Field trials in the Horonobe Underground Research Laboratory (URL) of the multi-interval displacement sensor developed using FBG technology are described. Laboratory tests were carried out to obtain the relational expression computed from the interrelationship of the variation in the Bragg wavelength, temperature and displacement. From the results of laboratory tests, accuracy of the sensor was evaluated to be better than ±0.5% of the measurement range. In situ monitoring at the Horonobe URL using the developed sensor was carried out in parallel with nearby monitoring using a conventional extensometer, which is an electrical signal system type, for verification of the developed sensor. The results of the in situ test indicate that the displacement values from both the sensor developed and the conventional extensometer are almost equivalent. One of the advantages of the developed sensor is the absence of noise in the monitoring data, in contrast to the data from a conventional extensometer.

Microstructure and origin of faults in siliceous mudstone at the Horonobe Underground Research Laboratory site, Japan

Fault-related microstructures and fault orientations in siliceous mudstone were studied at the Horonobe Underground Research Laboratory site in Japan. Thin dark bands define a weak foliation that exhibits compactional cataclastic fabrics in thin section. These fabrics were observed both along the faults and beyond the fault tips, in outcrop and in drill core. Most of the bands are so thin that it was not possible to measure their thickness in thin section. However, scanning electron microscope images of fault surfaces revealed evidence of chemical compaction within the bands. Millimeter-scale displacements occur along similar dark bands in diatomaceous mudstone, which overlies the siliceous mudstone. In all boreholes, the dominant orientation of unfolded faults is WNW–ESE strike and a near-vertical dip. These observations suggest that the faults formed along compactional shear bands that in turn nucleated under ductile or brittle–ductile conditions. The development of compactional shear bands preceded fault formation, occurring just prior to folding, in response to E–W compression related to the eastward migration of the Amurian plate.

The relationships among brittleness, deformation behavior, and transport properties in mudstones: An example from the Horonobe Underground Research Laboratory, Japan

[1] Mudstones are low-permeability sedimentary rocks; however, when shear stresses induced by tectonic movement or nonhydrostatic stresses exceed the shear strength of the rock, brittle or ductile deformation occurs. The nature of this deformation is controlled by the brittleness of the mudstone. If brittle deformation occurs, the resulting dilatant structures may increase the permeability and change the transport properties of the strata. This paper addresses the relationships among brittleness, deformation behavior, and transport properties in mudstones at the Horonobe Underground Research Laboratory, Japan. Geological, mechanical, and hydrogeological data from borehole investigations and laboratory tests were systematically interpreted using a brittleness index (BRI), which is the ratio of the unconfined compressive strength to the effective vertical stress. For mudstones under natural strain rates and low temperatures, ductile deformation occurs when BRI 8, although semibrittle behavior may also occur at the brittle-ductile boundary. When BRI >8 and faulting is well developed, the mudstone behaves hydrogeologically as a fractured medium at the mesoscopic scale, whereas for BRI <8 the mudstone behaves hydrogeologically as a porous medium, even if faulting is extensive. The BRI concept is a useful tool for systematically characterizing the hydromechanical behavior of mudstones; for example, when assessing the effectiveness of mudstone as a long-term barrier in disposal repositories for radioactive waste.

Diffusion and sorption of Cs +, I − and HTO in samples of the argillaceous Wakkanai Formation from the Horonobe URL, Japan: Clay-based modeling approach

Diffusion and sorption behaviors of cationic Cs +, anionic I − and neutral HTO in samples of the Wakkanai Formation from the Horonobe underground research laboratory (URL), Japan, were investigated as a function of ionic strength ( I) of synthetic groundwater by through-diffusion and batch sorption experiments and mechanistic modeling. The effective diffusivities ( D e) measured by through-diffusion experiments showed cation excess and anion exclusion effects, which were strongly dependent on I; D e for Cs + decreased as I increased, D e for I − showed the opposite dependency and D e for HTO showed no dependence. The sorption of Cs + measured by through-diffusion and batch sorption experiments were described by Freundlich isotherms with consistent parameters and decreased with I as a result of competitive ion exchange. Diffusion and sorption behaviors were interpreted by assuming the clay components of illite and smectite control diffusion and sorption mechanisms. The component additive (CA) sorption model, which includes illite and smectite contents and their ion exchange constants, provided a reasonable account of the Cs + sorption trends measured as functions of I and Cs concentration. The diffusion model was developed by coupling the electrical double layer (EDL) model, describing the change of ionic concentrations (cation excess and anion deficit) and viscoelectric effects caused by electrostatic interaction at negatively charged clay surfaces, and a simplified pore model assuming one type of pore shape and includes their size distribution. When averaging the electrostatic effects by using the pore surface area distribution, the model could predict the cation excess and anion exclusion effects, and its dependence on I reasonably well. This result implies the nanoscale pores dominating the pore surface area can strongly impact on ionic diffusion in argillaceous rocks. The clay-based modeling approach described here provides a useful tool to predict ionic diffusion and sorption in argillaceous rocks.