ERE3.5

The construction and operational phases of a deep geological repository imply potential perturbations of the host rock, so-called Repository Induced Effects (RIE). Amongst them, spent fuel and high level waste (SF/HLW) produce decay heat even after long times of cooling, which may impair the long-term safety of the Engineered Barrier System and of the geological barrier. The Opalinus Clay (OPA), is currently being assessed as host rock for the deep geological repository in Switzerland. OPA is an indurated clay of Jurassic age (ca. 180 My), whose main features are (1) a very low hydraulic conductivity, (2) an excellent retention capacity for dissolved radionuclides, and (3) a significant self-sealing capacity.

The on-going Full-scale Emplacement (FE) Experiment at the Mont Terri Underground Rock Laboratory simulates, as realistically as possible, the construction, waste emplacement, backfilling and early-stage post-closure evolution of a single SF/HLW emplacement tunnel in OPA, using heaters instead of disposal canisters. The main goal of the FE experiment is the investigation of RIE on the host rock (and, to a lesser extent, on the the backfill material) at true scale and the validation of existing coupled thermo-hydro-mechanical (THM) models. In this context, Nagra has developed a new RD&D initiative, i.e., the FE modelling Task Force (FE-M TF), which involves three modelling teams with corresponding software packages (Code Aster, Code Bright and OpenGeoSys). So far, the TF has defined three main tasks:

• Code comparison and calculation verification: the TF designed a simplified (though realistic) 3D conceptual model of the FE experiment that includes the actual geometry of the main elements, materials and phases of the FE experiment, including tunnel excavation and ventilation. Such conceptual model was implemented by the modelling teams. Finally, code outputs were analysed and compared by the TF.
• Back-analyses of THM-observations in the host rock: monitoring data from radial
  and oblique boreholes around the backfilled FE tunnel are used for model calibration,
  including the derivation of parameter best estimates and inherent uncertainties, and model
• Model validation in the context of a prediction-evaluation exercise: the evolution
  of the THM conditions in the rock in response to a change of thermal loads (e.g., increase/decrease of heater output) will be predicted using the calibrated models. Finally, model predictions will be validated in the near future using the acquired measurements.

This presentation summarizes the current status of Tasks 1 and 2 and the path forward to Task 3.

How to cite: Alcolea, A., Damians, I. P., Firat-Lüthi, B., Garitte, B., Gens, A., Kolditz, O., Laloui, L., Lanyon, B., Madaschi, A., Marschall, P., Nagel, T., Olivella, S., Reinicke, A., Shao, H., Wang, W., and Wojnarowicz, M.: The FE-M Task Force: 3D modelling of THM repository induced effects in the Full-scale Emplacement Experiment (FE) – Mont Terri Rock Laboratory. Current status and the path forward., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13385, https://doi.org/10.5194/egusphere-egu22-13385, 2022.

Geological disposal of low and intermediate-level and high-level waste in Switzerland may - due to corrosion and degradation related processes - result in the production of gas. In our presentation we will focus on the integration of gas related processes and phenomena in the safety case and site selection. In addition, we will elaborate on what technical strategies Nagra follows to limit the potentially detrimental effects on the safety related properties of the technical and natural barriers.

Geological disposal of low and intermediate-level and high-level waste in Switzerland may - due to corrosion and degradation related processes - result in the production of gas. In our presentation we will focus on the integration of gas related processes and phenomena in the safety case and site selection. In addition, we will elaborate on what technical strategies Nagra follows to limit the potentially detrimental effects on the safety related properties of the technical and natural barriers.

How to cite: Leupin, O., Diomidis, N., Reinicke, A., and Papafotiou, A.: Nagra's Approach to Gas Release from Deep Geological Repositories, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13448, https://doi.org/10.5194/egusphere-egu22-13448, 2022.

Israel is assessing borehole disposal of radioactive waste. With limited geological options for disposal, intermediate-depth borehole disposal is being considered in the arid Yamin Plain region of the northeastern Negev desert at depths of several hundred meters below ground surface in the vadose zone. Unlike deep borehole disposal of several kilometers, which relies on emplacement below the depth of recirculating groundwater, the safety case for intermediate-depth borehole disposal relies more on the aridity of the vadose zone, the robustness of the engineered barriers (e.g., canister, seals, backfill materials) in the disposal borehole.

To study the suitability of the Yamin Plain region for borehole disposal a small-diameter characterization borehole is planned, to retrieve core samples and to better understand the vadose zone geo-mechanical and hydrogeochemical properties and percolation flux. Moreover, a wide range of laboratory geochemical, hydrological, and mechanical studies as well as a new seismic survey are being carried out. The information from the characterization borehole as well as the supplementary laboratory and seismic studies will inform the safety case, and together with performance assessment analyses will help to identify key areas of uncertainty and guide future research and development activities aimed at demonstrating the feasibility of the intermediate-depth borehole disposal concept in Israel.

How to cite: Klein-BenDavid, O., Freeze, G., Sassani, D., Calvo, R., Balaban, N., and Peer, G.: Borehole Disposal of Radioactive Waste in Israel, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8857, https://doi.org/10.5194/egusphere-egu22-8857, 2022.

The regionalized knowledge of the quality of near-surface rock masses is an important tool for land management/planning, as well as for guiding further in-depth studies aimed at landslide and earthquake risk assessment and civil engineering planning. The characterization of heterogeneous rock masses like flysch units represents a relevant challenge to engineering geologists due to the complex structure of these materials, which results from both their depositional context and tectonic history. Flysches are widespread all over the Apennines chain and their mechanical characterization is a difficult task given the occurrence of intercalation of layers with different lithology and strength. Moreover, the complexity of the thrust and fold tectonic framework makes the regional distribution of these characters difficult to predict. The aim of this work is to provide a method to map the near-surface rock masses quality for an arenaceous flysch widely cropping out in the outer Northern Apennines (Torrente Carigiola Formation, Aquitanian; Bettelli et al., 2002). This formation is mapped in both the geological map of the Regione Toscana (Italy) at the scale of 1:10,000 and the geological sheet “252 – Barberino di Mugello” (Bettelli et al., 2002) of the Italian Geological Map at the scale of 1:50,000 (CARG). It is made up by intercalated arenaceous (A) and pelitic (P) layers characterized by variable A/P ratio. The rock mass quality is evaluated by estimating, for a set of representative rock outcrops, the Rock Mass Quality Index (RQI; Disperati et al. 2016; Mammoliti et al. 2018). This index results from the analysis of both systematic Schmidt hammer rebound measurements (R) acquired at the nodes of a regular grid (ca. 20 R measurements for ca. 15-25 nodes) and the determination of the unit weight for representative outcrop rock samples. For the same outcrops, also the A/P ratio and bedding attitude are determined. The results show a positive linear correlation between RQI and the A/P ratio, confirming that the latter parameter is an important feature controlling the rock mass strength. This correlation is used to assess the distribution of both parameters within a set of geological cross sections traced normal to the regional structures trend (main thrusts and km-scale folds). Then, the structural features available from the literature geological maps allow us to extrapolate both the RQI and A/P ratio from the profiles to the map scale. Finally, a further set of the same rock outcrop data acquired after the above-described modelling procedure is used to check the accuracy of the method.

How to cite: Lombardi, G., D’Addario, E., Disperati, L., and Ferrarelli, F.: Engineering geological mapping of near-surface rock mass quality of folded and thrusted arenaceous flysch units in the Northern Apennines (Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11632, https://doi.org/10.5194/egusphere-egu22-11632, 2022.

The Republic of Serbia wishes to evaluate the various options for disposal of radioactive waste and used sources. The evaluation is supposed to be based on international solutions for radioactive waste, the current and future waste inventory of Serbia, and the various possible solutions for final disposal. A high-level assessment of the geological situation in Serbia, as well as an initial screening for suitable host rock material, is inherently included in such an evaluation, and is the aim of the current work.

Based on available information such as orohydrographical and morphostructural maps, the 1:300.000 geological map, individual but undisclosed 1:100.000 geological mapsheets, the 1:500.000 neo-Alpine tectonic map of Serbia, seismic hazard maps for different return periods, and various scientific publications dealing with the geological and tectonic evolution of Serbia and surroundings, several initial recommendations can be formulated that will support and assist the decision-making process in finding a suitable site (and host rock).

Roughly, the territory can be divided into two different regions with contrasting tectonic behaviour. South of the Danube, the relief intensity is significant and mountain massives with altitudes up to 2000 m and more are present. The most important morphostructural units include the Dinarides, the Vardar Zone, the Serbo-Macedonian Massif and the Carpatho-Balkanides. This region is characterised by outcropping and subcropping material that underwent significant deformation during various tectonic pulses in the past, resulting in a vast area with rather impermeable meta-sedimentary and metamorphic rocks. Neo-Alpine tectonics from the Oligo-Miocene onwards resulted in significant vertical uplift of the southern massifs, this pattern being interrupted by isolated and closed subsiding depressions. Throughout the region south of the Danube, magmatic rocks of various age, type and composition can be found, which are elsewhere being considered in international solutions for geological disposal. The same is valid for the previously mentioned meta-sedimentary and metamorphic rocks, which include flysch sequences, and several schist and gneiss occurrences.

North of the Danube, the Pannonian Basin is characterised by significant subsidence, up to several thousand meters since the Oligo-Miocene. The basin is filled with continental clastic deposits, with several prominent clay occurrences of sufficient thickness and depth. Clay rock and (plastic) unlithified clay are often being considered in international solutions for geological waste disposal.

The neo-Alpine tectonic map indicates the presence of numerous faults: gravitational, reverse and strike-slip. Quite a number of these have shown significant activity in the Pliocene and Quaternary, most notably those that mark the boundary between outcropping massifs and subsiding areas (e.g., between the Carpatho-Balkanides and the marginal part of the Pannonian Basin). Near those faults, historical seismic activity has been recorded with magnitudes up to M = 6.5. Seismic hazard seems to be highest in the central and southern part of the country.

In summary, this short geological reconnaisance of Serbia suggests that basic geological knowledge is available that will help evaluating the various disposal options, both in terms of host rock material (thickness and depth) and a stable geological environment.

How to cite: Beerten, K., Lenie, K., Stejić, P., and Arbutina, D.: Evaluation of the geological context for deep disposal options in Serbia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5103, https://doi.org/10.5194/egusphere-egu22-5103, 2022.

The potential host rock for the high-level nuclear waste repository of Hungary is the Boda Claystone Formation (BCF) located in SW Hungary, a homogeneous formation with a thickness of 1000 m. The BCF consists of well-compacted reddish-brown claystone, siltstone, and albitolite (authigenic albite >50%) with dolomite and sandstone intercalations. Fracture network modelling and hydrological assessment were performed in the BAF–2 well, which is over 900 m deep. The fracture network was modelled using a discrete fracture network (DFN) algorithm based on acoustic borehole televiewer (BHTV) images and core sample images. This modelling approach can be used to calculate the permeability and porosity of the fracture system if the hydrologic aperture of the fractures is known. Fracture aperture can be defined in several ways. In hydrodynamic processes, the hydraulic aperture should be used, which is defined as a theoretical conduit that produces the same flow rate as the real fracture. The hydraulic aperture was estimated using a calibration algorithm comparing the measured permeability values of the borehole to the modelled permeability values of the fracture system. Hydrological evaluation of the borehole was performed by calculating flow zone indices (FZI). This parameter is based on the covariation of porosity and permeability and is usually used to evaluate reservoir quality. FZI values denote hydraulic units within the rock column where the properties controlling flow are internally uniform. Based on the geometry of the fracture network and hydraulic flow units, most parts of the well behave uniformly, while three narrow zones exhibit different hydrologic characteristics. The first zone is located in the upper 100 m of the well and is likely formed by weathering and diagenetic processes. The second zone is at about 400 m, where a large-scale structural boundary is suspected. In the third zone at 700 m, coarsening of the host rock strongly affects the hydrological properties, but the influence of tectonic processes cannot be excluded either.

How to cite: Tóth, E., Hrabovszki, E., Félix, S., and Tivadar, M. T.: Fracture network modelling of a potential high-level nuclear waste repository site, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11213, https://doi.org/10.5194/egusphere-egu22-11213, 2022.

The work is based on long term work of Helsinki commission of Baltic sea and own field and laboratory researches. High rate of knowledge is possibility of forecast. The highest rate is possibility of control. Baltic sea has giant importance in Europe ecology, economic and policy as sea dividing and uniting many states. The growth of instability of environmental-climatic processes, an increase in the number of natural disasters, has been observed since the beginning of the XX century and requires the improvement of methods of environmental-climatic forecasts. The economic situation makes relevant low-cost and progressive forecasting methods. Of particular importance is the logical-mathematical modeling, combining two types of models - dynamic and static. Dynamic based on the analysis of trends. Static models are cheaper and more intellect. They are based on an assessment of the state of the systems (primarily ecological) at the moment, taking into account the element of anticipatory reflection characteristic of living systems. Monitoring the behavior of animals can be the basis of predictions and the creation of static prognostic models. An important and little developed direction of environmental forecasting is the phenogenetic indication. It is based on the analysis of morphologic characteristics of biological populations, quantitative and qualitative variability, sex ratio, sexual dimorphism. The level of development of population and ecological genetics makes this method a promising direction of environmental forecasting. Modeling of environmental processes in the Baltic zone requires taking into account both global processes (increase in climatic instability and the number of extreme natural events, increase in anthropogenic pressure), as well as regional processes (melting ice in the Arctic due to the “pseudo-greenhouse effect” and an increase in the concentration of methane in the atmosphere, cyclical changes in salinity with a period of 55 - 50 years, etc.). Comprehensive assessment of remote and contact monitoring data can be the basis for integrated static and dynamic modeling and a promising direction for the development of environmental safety. The expected trend in the Baltic zone for 10 to 20 years is a slight decrease in temperature, a continuing increase in the number of extreme events and an increase in the biomass and biodiversity of both desirable and undesirable species.

How to cite: Sapunov, V.: Ecological prediction of Baltic region basing on combination of static and dinamic modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-73, https://doi.org/10.5194/egusphere-egu22-73, 2022.

The knowledge of rock masses behaviour is an important information in various fields such as civil engineering, land use planning and hazard/risk zoning. Different rock mass classification methods, initially aimed at assisting underground excavations (Hoek, 2007), are widely used nowadays for preliminary design procedures (Bieniawski, 1989; Hoek, 2007), like the RMR (Bieniawski, 1976) and the Q (Barton et al., 1974) and their modifications. These methods incorporate geological, geomechanical and geometric parameters in order to obtain a quantitative estimation of the rock mass quality, but, on the other hand, their implementation is time-consuming. Despite the dominance of these two methods, further rock mass classifications systems have been proposed in the last decades and, among these, the Geological Strength Index (GSI) classification system is currently widely used as it allows to estimate the strength of rock mass through empirical semi-quantitative evaluation (Hoek, 1994; Cai et al., 2004), based on both rock mass structure and condition of the joints (Hoek et al., 1995). Estimating the GSI is straightforward and fast, but it comes at the cost of a certain degree of subjectivity. Moreover, the index does not adequately account for the lithology of the rock mass matrix. Hence, for the above reasons, these classification methods are not fully suitable to collect rock mass data over wide scale areas for engineering geological mapping. The Rock mass Quality Index (RQI, Disperati et al., 2016; Mammoliti et al., 2018) is a rock mass classification system developed for cartographic purposes and it is based on the systematic fieldwork measurement and processing of sets of the Schmidt hammer rebound values (R). Each representative rock mass outcrop is analysed by collecting ca. 20 R values at the 15-25 nodes of a regular grid conceived to investigate the typical features of the rock mass. This allows to perform statistical analyses and to calculate the RQI, a quantitative indicator of the global strength and quality of the rock mass. In the last decade, a dataset of ca 1100 outcrops sites spreading over a large area (ca. 12000 km²) were acquired in Tuscany (Italy), according to different lithology, weathering, jointing conditions. The dataset consists of both RQI measurements and GSI estimations for the main different lithological groups (flysch, limestones, marls, magmatic rocks and schists) of the Northern Apennines (Italy), as well as the laboratory determinations of the Slake Durability Index (Id2; Franklin & Chandra, 1974) obtained by testing representative outcrop rock samples. The large dataset has allowed to analyse the correlation among RQI, GSI and Id2 and to perform an in-depth critical analysis of the relationships among RQI, lithology, rock mass structure, as well as the suitability of the RQI as reference index for engineering geological mapping of near-surface rock mass quality.

How to cite: D'Addario, E., Disperati, L., Lombardi, G., and Marzini, L.: The Rock Mass Quality Index (RQI): a quantitative tool for the quality evaluation of near-surface rock masses, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7779, https://doi.org/10.5194/egusphere-egu22-7779, 2022.

Final radioactive waste disposal in deep crystalline bedrock demands a thorough understanding of flow and transport mechanics in sparsely fractured rock formations. The structural complexity and heterogeneity of crystalline bedrock, and the scarcity of field data for the hydraulic characterization motivates the development of multiple alternative conceptual and numerical models, both to test our understanding and to evaluate prediction uncertainties. Discrete fracture network (DFN) models are widely used in radioactive safety assessment programs in hard crystalline rocks while channel network models offer another representation of flow networks and preferential pathways, in line with indications that flow and transport in deep fractured media are usually dominated by a relatively small number of long preferential pathways. This study applied the channel network modeling approach to understand the hydraulic behavior in a fractured granite system (approximately 450 m deep), at the Äspö Hard Rock Laboratory in Sweden. The channel network model is built from a hydro-structural model of the site including known fracture geometries, with the help of a python scripting library, pychan3d. The study focused particularly on an evaluation of the usefulness of different characterization data to build and calibrate such a channel network model, and to compare this to a calibrated DFN model of the same site. An evolutionary algorithm (CMAES_P implemented in the PEST code) was used to semi-automatically calibrate the channel conductances in the channel network model against the field characterization data (flow rates, drawdowns, and tracer recoveries) in multiple phases. It was observed during the calibration process that some proposed CNM connectivity maps lent themselves to conductance calibration, while others failed to do so. Channel tortuosity and width were then critical to describe transport appropriately in terms of peak arrival and dispersion. The CNM was shown to be more responsive to calibration and to general alterations than a DFN with uniform fracture planes. After calibration, the CNM could match the flow measurements closer than the reference DFN model for the tested characterization phases. The CNM and DFN with the calibrated conductances and fitted geometric parameters were then used to investigate a long-term tracer transport scenario. This comparative study highlights the potential differences and associated uncertainties in the behavior of the two distinct types of models used in the study of crystalline hard rock fractured system.

How to cite: Dessirier, B., Sharma, K. M., Pedersen, J., Tsang, C.-F., and Niemi, A.: Calibration of a channel network model against Äspö field data and its application to long term prediction of tracer transport, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9706, https://doi.org/10.5194/egusphere-egu22-9706, 2022.

Clay rocks are investigated as potential host rocks for high-level nuclear waste (HLW) repositories in many countries. The Sandy Facies of Opalinus Clay (SF-OPA), as accessible in the Mont Terri rock laboratory, exhibits a pronounced heterogeneity, which is as well expected for lower cretaceous clay rocks, that are among the potential host rocks for the German HLW repository.

Aim of the DR-D experiment is to characterize the heterogeneity of SF-OPA on the m-cm scale via seismic tomography and borehole seismic characterization. Borehole logging and ex-situ drill core characterization provide information on rock heterogeneity on smaller scales.

Within the area, characterized by seismic tomography, a radio-tracer diffusion experiment will be set up, with the aim to correlate the observed diffusion behavior with the heterogeneous rock structure.

The first drilling campaign took place in May 2021. The seismic tomography survey of the experimental area was performed in October 2021. Processing and analysis of the seismic data, as well as drill core characterization are currently underway.

In this contribution we present the general concept and layout of the DR-D experiment, as well as first results.

We acknowledge funding by the German Federal Ministry of Education and Research (BMBF) (Grant 02NUK053A-E), the Helmholtz Association (Grant SO-093), BGR, and BGE. Special thanks to swisstopo and the Mont-Terri project for help, advice, and support.

How to cite: Heberling, F., Albers, H., Beilecke, T., Deissmann, G., Furche, M., Geckeis, H., Hoyer, E. M., Joseph, C., Liebscher, A., Lüth, S., Metz, V., Müller, K., Nowak, U., Rebscher, D., Schulte, F., Steegborn, F., and Tietz, T.: The DR-D experiment in the Mont-Terri rock laboratory, heterogeneity of the Sandy Facies of Opalinus Clay across scales, from seismic surveys to radionuclide diffusion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13268, https://doi.org/10.5194/egusphere-egu22-13268, 2022.

In deep geological repositories for nuclear waste, groundwater may saturate the (geo-) technical barriers, and waste container corrosion may be occurring. This may finally lead to radionuclides being released from the waste [1]. The sorption capacity of potential host rocks, such as crystalline rocks and clay rocks, and of potential secondary phases is an essential aspect in the Safety Case. Barite (BaSO₄) can be present in crystalline rocks as a fracture filling material. In clay rocks, sulfate minerals ((Ba,Sr)SO₄) are found as accessories. Barium (Ba) is present in the waste as a fission product and as sulfate containing groundwater contacts the waste, barite may form. Ra uptake by barite occurs when dissolved Ra reacts with barite, leading to Ra retention by (Ba,Ra)SO₄ solid-solution formation [2]. Barite reaction with aqueous carbonate at high pH, e.g. due to cementitious material alteration inside a repository, may cause barite to convert into witherite (BaCO₃) [3]. The presence of carbonate likely alters the chemical behaviour of barite surfaces, via surface mixing or by witherite layer formation through dissolution-precipitation [4]. Aim of this study is to investigate the effect of carbonate on Ra retention by barite.

The presented results highlight barite transformation into witherite in the absence and presence of Ra. Barite suspensions were contacted with carbonate solutions (1-100 mM, pH 7-11). X-ray diffraction (XRD) showed shifts of reflection peaks in batches with pH 9-11 and carbonate concentrations of 10-100 mM, indicating a witherite-barite solid-solution formation [3], though this is not energetically favorable according to Density Function Theory calculations. Reaction rates depend on the type of barite. Generally, reactions slow down after about 7 days, likely due to surface passivation. Cubes of natural barite were reacted with 100 mM carbonate solutions at pH 11. As a result, a porous witherite layer with (271±32) μm formed, giving insight into recrystallization process progress and mechanism. Atomic Force Microscopy measurements were conducted for witheritegrowth. Barite was equilibrated at 35°C and contacted with a carbonate solution (0.01M, pH 10). Orientated particles with different shapes grew. More measurements will be conducted with different conditions to obtain a distinct growth. For Ra uptake, witherite batches(S/L 0.01, pH 8.7) were prepared for Ra to be spiked subsequently.  

We acknowledge KACST funding and the German federal ministry for education and research for funding the travel through the collaborative project KRIMI, grant agreement 02NUK056A.

[1]       Curti, E., et al. (2010) Geochim. Cosmochim. Acta 74.12, 3553-3570.

[2]        Heberling et al. (2018) Geochim. Cosmochim. Acta 232, 124-139.

[3]        Rendón-Angeles et al. (2008) J. Materials Science 43, 2189-2197.

[4]        Putnis and Putnis (2007) J. Solid State Chemistry 180, 1783-1786.

How to cite: Alzaydan, M., Roth, T., Heberling, F., Polly, R., Schild, D., and Metz, V.: Barite Recrystallization to Witherite in the Presence of Carbonate, and the Impact on Radium Retention, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13412, https://doi.org/10.5194/egusphere-egu22-13412, 2022.

Column experiments are more sensitive to surface reactions than batch studies due to the increased surface area to liquid volume ratio. Moreover, these dynamic set-ups allow for stringent tests concerning the validity of equilibrium models for surface protonation and adsorption of pollutants.  In the present study, column experiments were carried out at constant pH, where the concentration of background electrolyte consisting of monovalent electrolytes like NaCl at the inlet were varied. Due to the charging phenomena caused by ionic-strength dependent acid-base reaction, the pH at the outlet of column varied. On a positively charged surface (such as alumina at pH 5.8) the increase in salt concentration at the inlet caused a transient increase in pH due to enhanced protonation of surface hydroxyls. On a negatively charged surface (PTFE at pH 5.8) the increase in salt concentration caused a decrease in pH at the column outlet due to enhanced uptake of hydroxide ions at higher salt concentrations. The charging behavior of both surfaces was independently determined by streaming potential measurements. For PTFE column experiments at different pH values were carried out to further relate them to the streaming potential data. Indeed below the isoelectric point, the trend of the pH-jump at the outlet of the column was inversed which suggests pH dependent charging of this inert surface due to protons and hydroxide ions.

Overall, the experiments show the high sensitivity of column experiments to changes in solution composition and the kind of experiments may allow for determining points of zero charge in an elegant way.

How to cite: Lützenkirchen, J., Hanna, K., and Marsac, R.: Evolution of pH induced by salt concentration change under flowthrough conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13279, https://doi.org/10.5194/egusphere-egu22-13279, 2022.

Natural uranium (U) in deep groundwater has been extensively studied in connection to the search for suitable locations for final disposal of spent nuclear fuel (SNF).[1] The U removal process depends on environmental and geochemical conditions and is often associated with fractionation of the main ‘stable’ isotopes, ²³⁸U and ²³⁵U (δ²³⁸U). The latter thus serves as an important tracer for redox specific scenarios, in local to global temporal and spatial scales. In this contribution, one specific borehole drilled at 415 m depth into Paleoproterozoic granitoid rock at the Äspö Hard Rock Laboratory (HRL), Sweden, is investigated after 17-year experiment period (1995-2012).[2] The HRL is built and operated by the Swedish Nuclear Fuel and Waste Management Co. and serves as a full-scale tunnel as a test-facility for the actual SNF repository to be built at Forsmark. We show how various micro-analytical techniques, modelling methods, and isotope analyses can be utilized to reveal U speciation and removal pathways, associated redox changes and related U isotope fractionations in the deep aquifer and during U mineralogical trapping. Spectroscopic techniques reveal that calcite precipitated on the borehole equipment contains intermittent highly elevated U, occurring as U(IV), and thus serves as a sink for U. Thermodynamic modelling shows that aqueous Fe(II) is the main driving force for the reduction of U(VI) in the borehole water, alongside sulfides formed from bacterial sulfate reduction. The bacteria-driven degradation of technical polymer constituents present in the borehole equipment is central to processes forming the sulfides and carbonates that facilitate reduction of U(VI) and subsequent immobilisation of U(IV) into the calcite. We use δ²³⁸U to show that U undergoes several redox events in granitic rock aquifers, involving mineralogical and microbial pathways. The recorded δ²³⁸U provides evidence for reductive removal of U from fracture water, presumably taking place along redox fronts in the fracture network. The obtained data on U(IV) removal by calcite provide important insights for the assessment of the geochemical behaviour of U and other redox-sensitive species in deep anoxic aquifers, that is relevant for trace metal mobility and long-term storage of SNF and nuclear waste.

References

[1]. J. Suksi et al., (2021), Chemical Geology 584: 120551.

[2]. H. Drake et al., (2018), Environmental Science & Technology 52(2): 493-502.

How to cite: Pidchenko, I., Christensen, J., Puigdomenech, I., Ignatyev, K., and Drake, H.: Assessing long-term microbial impact on mineralogical trapping of uranium from deep groundwater at Äspö Hard Rock Laboratory, Sweden, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5534, https://doi.org/10.5194/egusphere-egu22-5534, 2022.

Earlier (GeoBio 2014, Moscow ) it was reported that an independent domain is observed in the Earth's Сrust - the Hydrocarbon Sphere (HCS). HCS is a sequential alternation of hydrocarbon fields in accordance with geological objects. HCS is a material space-time continuum spread throughout Earth Crust, from Archean to modern precipitation. On the scale of the Earth's crust, HCS is represented by the entire HC spectrum (light CH₄, heavy HHC, normal, isoforms, etc.). Globally, chemically, the HCS gas composition of the Earth's Crust of the granite layer is similar to the HCS composition of gas fields and is equal to CH₄-HHC, while the basalt layer corresponds to the HCS composition of oil fields and is equal to HHC - CH₄. Structure of HCS   of the Earth Crust based on 1 layer  Мodel of the Earth's Crust Galant (MECG), ( AAPG Athens 2007, EGU Vienna 2013) сonsist of separated layers of CH₄-HHC (Granite HC Sphere)and separated layers of HHC - CH₄ (Basalt HC Sphere ).   Considering that, according to the MECG model, “there is no basalt crust under the granite crust, and there is no granite crust under the basalt crust”, both HCS of the Earth's Crust - Granite HC Sphere and Bazalt HC Sphere lies directly on mantle.

How to cite: Galant, Y.: Structure of the Hydrocarbon Sphere of the Earth's Crust, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-789, https://doi.org/10.5194/egusphere-egu22-789, 2022.

 In order to assess the reaction Enguri Dam nearby fault systems a monitoring system to study the seismicity and geodynamic situation has been set-up in recent years. To monitor the development of geodynamic processes, boreholes in the vicinity of the dam have been logged, intensively and permanent water level, temperature and conductivity monitoring was installed and where those parameters observations started to provide information about the stress field variation. The EGU presentation will introduce the different monitoring systems and present first results of data analysis. It also will show how repeated monitoring in boreholes can provide insight in the system stability.

How to cite: Goguadze, N., Melikadze, G., Mueller, B., and Niederhuber, T.: Assessment of the condition of Enguri High Dam in Georgia: the organisation of geodynamic monitoring, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11455, https://doi.org/10.5194/egusphere-egu22-11455, 2022.