Rapport final du projet européen CatClay sur les processus de migration des cations dans les roches argileuses indurées

International audienceIn the framework of the feasibility studies on the radioactive waste disposal in deep argillaceous formations, it isnow well established that the transport properties of solutes in clay rocks, i.e. parameter values for Fick’s law, are mainlygoverned by the negatively charged clay mineral surface. While a good understanding of the diffusive behaviour of non-reactiveanionic and neutral species is now achieved, much effort has to be placed on improving understanding of coupledsorption/diffusion phenomena for sorbing cations. Indeed, several cations known to form highly stable surface complexes withsites on mineral surfaces migrate more deeply into clay rock than expected. Therefore, the overall objective of the EC CatClayproject is to address this issue, using a ‘bottom-up’ approach, in which simpler, analogous systems (here a compacted clay,‘pure’ illite) are experimentally studied and modelled, and then the transferability of these results to more complex materials, i.e.the clay rocks under consideration in France, Switzerland and Belgium for hosting radioactive waste disposal facilities, isverified. The cations of interest were chosen for covering a representative range of cations families: from a moderately sorbingcation, the strontium, to three strongly sorbing cations, Co(II), Zn(II) and Eu(III). For the 4 years of this project, much effort wasdevoted to developing and applying specific experimental methods needed for acquiring the high precision, reliable data neededto test the alternative hypotheses represented by different conceptual-numerical models. The enhanced diffusion of the sorbingcations of interest was confirmed both in the simpler analogous illite system for Sr2+, Co(II) and Zn(II), but also in the naturalclay rocks, except for Eu(III). First modelling approach including diffusion in the diffuse double layer (DDL) promisinglysucceeded in reproducing the experimental data under the various conditions both in illite and clay rocks, even though someassumptions made have to be verified. In parallel, actual 3D geometrical pore size distributions of compacted illite, and in lessextent, clay rock samples, were successfully determined by combining TEM and FIB-nt analyses on materials maintained in awater-like saturation state by means of an extensive impregnation step. Based on this spatial distribution of pores, first numericaldiffusion experiments were carried at the pore scale through virtual illite, enabling a better understanding of how transferpathways are organized in the porous media. Finally, the EC CatClay project allowed a better understanding of the migration ofstrongly sorbing tracers through low permeability ‘clay rock’ formations, increasing confidence in our capacity to demonstratethat the models used to predict radionuclide migration through these rocks are scientifically sound

Dissolved noble gases and stable isotopes as tracers of preferential fluid flow along faults in the Lower Rhine Embayment, Germany

Groundwater in shallow unconsolidated sedimentary aquifers close to the Bornheim fault in the Lower Rhine Embayment (LRE), Germany, has relatively low δ2H and δ18O values in comparison to regional modern groundwater recharge, and 4He concentrations up to 1.7 × 10−4 cm3 (STP) g–1 ± 2.2 % which is approximately four orders of magnitude higher than expected due to solubility equilibrium with the atmosphere. Groundwater age dating based on estimated in situ production and terrigenic flux of helium provides a groundwater residence time of ∼107 years. Although fluid exchange between the deep basal aquifer system and the upper aquifer layers is generally impeded by confining clay layers and lignite, this study’s geochemical data suggest, for the first time, that deep circulating fluids penetrate shallow aquifers in the locality of fault zones, implying  that sub-vertical fluid flow occurs along faults in the LRE. However, large hydraulic-head gradients observed across many faults suggest that they act as barriers to lateral groundwater flow. Therefore, the geochemical data reported here also substantiate a conduit-barrier model of fault-zone hydrogeology in unconsolidated sedimentary deposits, as well as corroborating the concept that faults in unconsolidated aquifer systems can act as loci for hydraulic connectivity between deep and shallow aquifers. The implications of fluid flow along faults in sedimentary basins worldwide are far reaching and of particular concern for carbon capture and storage (CCS) programmes, impacts of deep shale gas recovery for shallow groundwater aquifers, and nuclear waste storage sites where fault zones could act as potential leakage pathways for hazardous fluids

Mineralogical attenuation for metallic remediation in a passive system for mine water treatment

Passive systems with constructed wetlands have been consistently used to treat mine water from abandoned mines. Long-term and cost-effective remediation is a crucial expectation for these water treatment facilities. To achieve that, a complex chain of physical, chemical, biological, and mineralogical mechanisms for pollutants removal must be designed to simulate natural attenuation processes. This paper aims to present geochemical and mineralogical data obtained in a recently constructed passive system (from an abandoned mine, Jales, Northern Portugal). It shows the role of different solid materials in the retention of metals and arsenic, observed during the start-up period of the treatment plant. The mineralogical study focused on two types of materials: (1) the ochre-precipitates, formed as waste products from the neutralization process, and (2) the fine-grained minerals contained in the soil of the wetlands. The ochre-precipitates demonstrated to be poorly ordered iron-rich material, which gave rise to hematite upon artificial heating. The heating experiments also provided mineralogical evidence for the presence of an associated amorphous arsenic-rich compound. Chemical analysis on the freshly ochre-precipitates revealed high concentrations of arsenic (51,867 ppm) and metals, such as zinc (1,213 ppm) and manganese (821 ppm), indicating strong enrichment factors relative to the water from which they precipitate. Mineralogical data obtained in the soil of the wetlands indicate that chlorite, illite, chlorite–vermiculite and mica–vermiculite mixedlayers, vermiculite, kaolinite and goethite are concentrated in the fine-grained fractions (<20 and <2 μm). The chemical analyses show that high levels of arsenic (up to 3%) and metals are also retained in these fractions, which may be enhanced by the low degree of order of the clay minerals as suggested by an XRD study. The obtained results suggest that, although the treatment plant has been receiving water only since 2006, future performance will be strongly dependent on these identified mineralogical pollutant hosts.Fundação para a Ciência e a Tecnologia (FCT

Isotopic evidence (⁸⁷Sr/⁸⁶Sr, δ⁷Li) for alteration of the oceanic crust at deep-rooted mud volcanoes in the Gulf of Cadiz, NE Atlantic Ocean [(Sr-87/Sr-86, delta Li-7) ]

The chemical and isotopic composition of pore fluids is presented for five deep-rooted mud volcanoes aligned on a transect across the Gulf of Cadiz continental margin at water depths between 350 and 3860 m. Generally decreasing interstitial Li concentrations and Sr-87/Sr-86 ratios with increasing distance from shore are attributed to systematically changing fluid sources across the continental margin. Although highest Li concentrations at the near-shore mud volcanoes coincide with high salinities derived from dissolution of halite and late-stage evaporites, clayey, terrigenous sediments are identified as the ultimate Li source to all pore fluids investigated. Light delta Li-7 values, partly close to those of hydrothermal vent fluids (delta Li-7: +11.9 parts per thousand), indicate that Li has been mobilized during high-temperature fluid/sediment or fluid/rock interactions in the deep sub-surface. Intense leaching of terrigenous clay has led to radiogenic Sr-87/Sr-86 ratios (similar to 0.7106) in pore fluids of the near-shore mud volcanoes. In contrast, non-radiogenic Sr-87/Sr-86 ratios (similar to 0.7075) at the distal locations are attributed to admixing of a basement-derived fluid component, carrying an isotopic signature from interaction with the basaltic crust. This inference is substantiated by temperature constraints from Li isotope equilibrium calculations suggesting exchange processes at particularly high temperatures (&gt;200 degrees C) for the least radiogenic pore fluids of the most distal location.Advective pore fluids in the off-shore reaches of the Gulf of Cadiz are influenced by successive exchange processes with both oceanic crust and terrigenous, fine-grained sediments, resulting in a chemical and isotopic signature similar to that of fluids in near-shore ridge flank hydrothermal systems. This suggests that deep-rooted mud volcanoes in the Gulf of Cadiz represent a fluid pathway intermediate between mid-ocean ridge hydrothermal vent and shallow, marginal cold seep. Due to the thicker sediment coverage and slower fluid advection rates, the overall geochemical signature is shifted towards the sediment-diagenetic signal compared to ridge flank hydrothermal environments. (C) 2009 Elsevier Ltd. All rights reserved

Scaling Behavior of Human Locomotor Activity Amplitude: Association with Bipolar Disorder

Scale invariance is a feature of complex biological systems, and abnormality of multi-scale behaviour may serve as an indicator of pathology. The hypothalamic suprachiasmatic nucleus (SCN) is a major node in central neural networks responsible for regulating multi-scale behaviour in measures of human locomotor activity. SCN also is implicated in the pathophysiology of bipolar disorder (BD) or manic-depressive illness, a severe, episodic disorder of mood, cognition and behaviour. Here, we investigated scaling behaviour in actigraphically recorded human motility data for potential indicators of BD, particularly its manic phase. A proposed index of scaling behaviour (Vulnerability Index [VI]) derived from such data distinguished between: [i] healthy subjects at high versus low risk of mood disorders; [ii] currently clinically stable BD patients versus matched controls; and [iii] among clinical states in BD patients

FCC-ee: The Lepton Collider: Future Circular Collider Conceptual Design Report Volume 2

In response to the 2013 Update of the European Strategy for Particle Physics, the Future Circular Collider (FCC) study was launched, as an international collaboration hosted by CERN. This study covers a highest-luminosity high-energy lepton collider (FCC-ee) and an energy-frontier hadron collider (FCC-hh), which could, successively, be installed in the same 100 km tunnel. The scientific capabilities of the integrated FCC programme would serve the worldwide community throughout the 21st century. The FCC study also investigates an LHC energy upgrade, using FCC-hh technology. This document constitutes the second volume of the FCC Conceptual Design Report, devoted to the electron-positron collider FCC-ee. After summarizing the physics discovery opportunities, it presents the accelerator design, performance reach, a staged operation scenario, the underlying technologies, civil engineering, technical infrastructure, and an implementation plan. FCC-ee can be built with today’s technology. Most of the FCC-ee infrastructure could be reused for FCC-hh. Combining concepts from past and present lepton colliders and adding a few novel elements, the FCC-ee design promises outstandingly high luminosity. This will make the FCC-ee a unique precision instrument to study the heaviest known particles (Z, W and H bosons and the top quark), offering great direct and indirect sensitivity to new physics

Salt-freshwater dynamics in a subterranean estuary over a spring-neap tidal cycle

This paper presents field measurements and numerical simulations of pore water salinities and groundwater flow in the intertidal zone of an unconfined coastal aquifer over a spring-neap tidal cycle. The study provides insight into the extent and time-scales of mixing between fresh groundwater and recirculating seawater in a tidally influenced subterranean estuary. Salt-freshwater dynamics in subterranean estuaries are currently not well understood despite their potentially important implications for fluxes of chemicals to coastal waters via submarine groundwater discharge. The data and simulation results show that changes in the tidal shoreline excursion over the spring-neap cycle induce significant variations in the intertidal salinity structure. Observed higher frequency salinity fluctuations demonstrate further the intensity and complexity of the salt-freshwater mixing process. In contrast with the salinity variations, fresh groundwater was found to discharge around a distinct intertidal beach slope break throughout the spring-neap period. This suggests that the slope break may affect significantly groundwater flow and salt transport near the shore. Measurements of pH and dissolved oxygen distributions revealed important biogeochemical zonations in the system. These zonations are expected to strongly influence the fate of many reactive chemicals in the nearshore aquifer and their subsequent discharge to coastal waters