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

Mobility of selenium oxyanions in clay-rich media: A combined batch and diffusion experiments and synchrotron-based spectroscopic investigation

International audienceSelenium-79 is considered as a critical radionuclide in safety assessment of high-level radioactive waste deep geological repository in clay-rich formations, owing to its long halflife and its anionic form in three relevant oxidation states (VI, IV,-II). An in-depth understanding of the diffusive transport properties of Se is therefore essential, especially due to its high sensitivity to oxido-reduction conditions. Here, the mobility of selenite and selenate in claystone samples (Callovo-Oxfordian, East of Paris Basin, France) under anoxic conditions is assessed by combining batch and diffusion experiments, and synchrotron-based spectroscopic mapping of diffusion fronts. Results showed that selenite and selenate behaved distinctly. Selenate diffused similarly to the reference anionic tracer, $^{36}$Cl$^-$, without significant sorption or reduction. Selenite showed a sorption behaviour that increased with the decrease of the initial concentration from 10$^{-3}$ to 10$^{-6}$ mol L$^{-1}$ , values of distribution ratio (R$_d$) from batch experiments ranging from 10 to about 250 mL g$^{-1}$. Selenite in-diffusion experiments showed that a pure diffusion model with reversible sorption was able to roughly reproduce the evolution of dissolved selenite in solution over time. However, additional reactions were required to properly describe the irregular shape of the selenite diffusion profiles in the solid. Mapping of Se oxidation state in diffusion fronts within the claystone coupons showed the presence of reduced Se (Se (0), Se(-I) and/or Se(-II)) along a fringe located at about 2 mm beneath the surface, possibly explaining the irregular shape of diffusion profiles. In the superficial zone (0 to 2 mm), oxidizing perturbations are assumed to account for the preservation of selenite under this oxidation state. These perturbations would also bias batch results in the same manner. Deeper in the claystone sample, diffusing selenite was observed, with a content steadily decreasing up to 7 mm from the inlet. The results suggest that, even after more than 500 days of diffusion, Se reduction would occur progressively along the diffusion pathways

Deep remission on magnetic resonance imaging impacts outcomes of perianal fistulizing Crohn’s disease

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Diffusion d'eau et d'ions dans la kaolinite compactée partiellement saturée en eau : rôle joué par la diffusion en phase vapeur dans la mobilité de l'eau

The results presented are part of the Ph.D. thesis of J.W. granted by Andra and CEAInternational audienceDiffusion is the main transport process of water and solutes in clay-rich porous media owing to their very low permeability, so they are widely used as barriers against contaminant spreading. However, the prediction of contaminant mobility can be very complicated when these media are partially water-saturated. We conducted diffusion experiments for water (HTO and HDO) and ions (22 Na + and 125 I −) through partially water saturated compacted kaolinite, a weakly charged clay material, to quantify the distinct diffusive behavior of these species. The osmosis method was used to set kaolinite samples at 67, 86 and 100% saturation. The results showed that desaturation led to a sharp decrease in diffusive rates by factors of 6.5, 18 and 35 for HTO, 125 I − and 22 Na + , respectively, from 100 to 67% of the degree of saturation. Thus, to interpret water diffusivities, we proposed a model taking into account the diffusion of water in both gas and liquid phases, using diffusion data obtained for ions, considered as inert species. This model was capable of properly predicting water diffusive flux, especially at a low degree of saturation (67% saturation), for which the assumption made for the occurrence of air phase continuity throughout the sample appears to be more relevant than at 86% saturation.La diffusion est le principal processus de transport de l'eau et des solutés dans les milieux poreux riches en argile en raison de leur très faible perméabilité, ils sont donc largement utilisés comme barrières contre la propagation des contaminants. Cependant, la prédiction de la mobilité des contaminants peut être très compliquée lorsque ces milieux sont partiellement saturés en eau. Nous avons mené des expériences de diffusion pour l'eau (HTO et HDO) et les ions (22 Na + et 125 I −) à travers de la kaolinite compactée partiellement saturée d'eau, un matériau argileux faiblement chargé, pour quantifier le comportement diffusif distinct de ces espèces. La méthode d'osmose a été utilisée pour régler les échantillons de kaolinite à 67, 86 et 100 % de saturation. Les résultats ont montré que la désaturation entraînait une forte diminution des taux de diffusion par des facteurs de 6,5, 18 et 35 pour HTO, 125 I − et 22 Na + , respectivement, de 100 à 67 % du degré de saturation. Ainsi, pour interpréter les diffusivités de l'eau, nous avons proposé un modèle prenant en compte la diffusion de l'eau dans les phases gazeuse et liquide, en utilisant les données de diffusion obtenues pour les ions, considérés comme des espèces inertes. Ce modèle était capable de prédire correctement le flux diffusif de l'eau, en particulier à un faible degré de saturation (67 % de saturation), pour lequel l'hypothèse faite pour l'occurrence de la continuité de la phase de l'air dans tout l'échantillon semble plus pertinente qu'à 86 % de saturation

Reconstitution paléo-environnementale du bassin versant du lac Bénit (Haute-Savoie, France) au cours des 2300 dernières années : impact des activités humaines sur l’écologie du lac.

PosterInternational audienceLe lac Bénit (1450 m) en Haute-Savoie est le lieu d’activités touristiques, pastorales, et halieutiques. Les conséquences de ces différentes activités sur ce lac sont encore mal connues. L’objectif de cette étude est de retracer l’évolution de son état trophique en lien avec les différentes pratiques, en s’intéressant à son enregistrement sédimentaire. Une carotte de sédiments d’un mètre a été prélevée au centre du lac et datée à partir de radioéléments de courtes périodes et de mesures du 14C. Une analyse multiproxies a été entreprise en associant analyses sédimentaires (granulométrie, perte au feu), palynologique et géochimiques (XRF, dosages CNP), du sédiment et des sols de la zone littorale du lac. La séquence sédimentaire couvre les derniers 2300 ans. Entre 300 cal. BC et 860 cal. AD, le rapport C/N et la proportion de MO (matière organique) sont élevés et suggèrent une relation lac-bassin versant caractérisée par des transferts dissous et de la MO réfractaire. Ces transferts pourraient traduire un état oligotrophe du lac favorisé par la présence d’un couvert forestier. A partir de 860 cal. AD, la proportion de MO diminue, la fraction terrigène et le taux de sédimentation augmente de 0,2 à 0,8 mm/an avec l’ouverture du milieu. Cette augmentation des apports terrigènes pourrait avoir été favorisée par une déforestation et une intensification des pratiques agro-pastorales durant la période médiévale. La déprise pastorale, à partir de 1940 cal. AD, entraine le retour de ligneux sur le bassin versant. Une buvette est installée au bord du lac en 1952. Le niveau du lac est rehaussé en 1964 pour faciliter la pêche, engendrant l’inondation des sols au bord du lac. Ce rehaussement coïncide avec l’augmentation de la concentration en phosphore assimilable dans le sédiment. On observe également une diminution graduelle de la quantité de phosphore assimilable des sols émergés vers les sols immergés. La hausse récente de la teneur en phosphore pourrait être due à un relargage de celui-ci depuis les sols immergés, anciennement pâturés, lors de la remontée du niveau du lac en 1964. Elle pourrait être liée également à l’intensification du tourisme dans le bassin versant. Cette étude met donc en évidence i) un changement majeur de la sédimentation à l’époque médiévale en lien avec un changement de l’occupation des sols sur le bassin versant et ii) une augmentation du phosphore sur les cinquante dernières années suite aux différentes activités agropastorales, puis de loisirs, modifiant les conditions trophiques de ce lac

Impact of Extra-Intestinal Manifestations at Diagnosis on Disease Outcome in Pediatric- and Elderly-Onset Crohn′s Disease: A French Population-Based Study

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National observation infrastructures in a European framework: COAST-HF A fixed-platform network along French coasts

COAST-HF (Coastal OceAn observing SysTem – High Frequency) is a French national observation network of the physical and biogeochemical dynamics of the coastal ocean, at high frequency. COAST-HF aims at understanding and analysing changes of contrasted coastal ecosystems at different temporal scales from extreme or intermittent high frequency (hour, day) events to multi-year trends. Since several years (from 2000 for the longest time series in Bay of Brest), the network extends along the English Channel, Atlantic and Mediterranean French coasts through 14 fixed platforms instrumented for the in situ high-frequency (≤ 1h) observations. Several French research institutes (IFREMER, CNRS, Marine Universities) are operating these systems. The organization of continuous multi-site in situ observations in a unique network of coastal observing platforms aims at operating an optimal system to pool efforts and initiatives (e.g. human resources for data management), to converge on best practices, and to support common measurement standards. On this basis, key scientific questions can be addressed such as eutrophication processes and effects on dissolved oxygen concentration and phytoplankton dynamics (i.e. in vivo fluorescence), or the influence of main river plumes on sediment dynamics. This coastal in situ observing network contributes for sustained high frequency and long-term observations in coastal environment based on Essential Ocean Variables. Ongoing technological and methodological developments are investigating the continuous observation of chemical (e.g. pCO2, pH) and biological features (e.g. phytoplankton diversity, primary production) that are being implemented in some of these platforms. COAST-HF is part of a national infrastructure (ILICO) and of the European Research Infrastructure project JERICO-NEXT. All those observations are connected to national, regional and European observatory networks and initiatives as the European Ocean Observing System