Porewater chemistry of Opalinus Clay revisited: Findings from 25 years of data collection at the Mont Terri Rock Laboratory.

The characterisation of porewater chemistry in nanoporous clayrocks is a difficult task. Appropriate extraction methods that have been developed fairly recently and the Mont Terri Rock Laboratory (Switzerland) have played a pioneer role in this regard. During the last 25 years high-quality data from the Opalinus Clay have been acquired. Notably, since the early synthesis of Pearson et al. (2003) a considerable number of newer data from borehole waters and waters extracted from drillcores have been generated. In this study, borehole, squeezing, leaching and cation exchange data were critically evaluated in order to derive a consistent porewater chemistry database across the formation. The results underline that the porewater composition is not constant but exhibits a regular change towards the formation boundaries. This is explained by diffusive exchange between the Na–Cl type porewater and the two bounding freshwater aquifers. Furthermore, the porewater is constrained by cation exchange, carbonate mineral and celestite equilibria. Major solute data obtained from borehole waters and squeezed waters are broadly consistent, although the latter exhibit somewhat more scatter. Overall, the knowledge on porewaters at the Mont Terri Rock Laboratory has been significantly improved. In particular, this regards the spatial profiles of major elements besides Cl, and better constraints on exchanger composition and pH/pCO2 conditions

Evaluation and Comparison of Content Management Systems

Appropriate information in time has developed to a main business resource and requires the same professional management as conventional means of production. However, the huge supply as well as the customary decentralized storage are aggravating the effective handling of information. Content management approaches to unify the administration of relevant information. There are developing a vast number of software products which aim to apply this concept. However, a clear definition of content management does not exist and thus, the market offers a variety of solutions. This bachelor thesis analyzes four content management systems (IBM Content Manager, Hyperwave Information Server, Zope, VIP Content Manager) which represent different aspects of content management, such as Web content management, collaboration in Intranets or management of multimedia. As a basis, general comparison criterions are developed, which orientate to the content life cycle. Examples of application areas for each system conclude the comparison

Modelling of solute transport and microbial activity in diffusion cells simulating a bentonite barrier of a spent nuclear fuel repository

Microbial sulfate reduction possesses a potential risk for the long-term safety of spent nuclear fuel repositories because under expected repository conditions sulfide is the main corroding agent for copper and copper-coated steel canisters foreseen in the Scandinavian disposal concepts. It is thus essential to understand and quantify the processes and factors impacting microbial sulfide production within and around compacted bentonite, which is planned to be used as a buffer material in many repository concepts. In the present study reactive transport modelling was applied to increase the understanding of diffusion cell experiments, which brought sand layers with or without inoculated microorganisms in contact with compacted and saturated bentonites of different mineralogy. Model results obtained for a sodium bentonite from Wyoming and a calcium bentonite from Bulgaria gave strong evidence for the activation of bentonite indigenous microorganisms, at least in zones of a reduced density close to the bentonite/sand interface. For all experiments, the calculations indicated that after an initial phase of favourable conditions, microbial activity was limited by the (bio-)availability of organic carbon. In the Bulgarian bentonite, characterized by a very low gypsum content, the model furthermore suggested some in-termediate control of microbial sulfate reduction by sulfate availability. The present study thus demonstrated the rapid evolution of a transport limited system in settings where zones of microbial activity are in contact with highly compacted microbially-inactive bentonite. Gypsum dissolution calculated and determined experimentally for the Wyoming bentonite indicated significant gypsum dissolution in the first 2 cm from the interface during 450 days. The reactive transport model applied successfully in this study for the description of an experimental system followed the conceptual models for microbial sulfate reduction in repository settings. The results obtained offer insights regarding the mechanism and magnitude of biogeochemical reactions that might occur in the vi-cinity of the bentonite buffer surrounding the waste canister and in so doing, may be relevant for the near field of HLW repositories

3D modelling of long-term sulfide corrosion of copper canisters in a spent nuclear fuel repository

Copper canisters are a central component in the safety of the Finnish spent fuel repository concept (KBS-3), where the main corrodent potentially affecting the canister integrity is sulfide. In this study, a 3D numerical model is developed to assess the evolution of sulfide fluxes and the spatially resolved canister corrosion depths for the Finnish spent nuclear fuel repository concept. The backfilled tunnel and the disposal hole are implemented using repository geometries, with sulfide being produced at their interface with the rock (excavation damaged zone) by sulfate reducing bacteria (SRB). Recent experimental findings regarding the microbial sulfate reduction process as well as the scavenging of sulfide via iron (oxy)hydroxides are incorporated in the reactive transport model. Long-term simulations are performed, predicting a heterogeneous corrosion of the canister with a max. corrosion depth of 1.3 mm at the bottom corner after one million years. The evolution of sulfide fluxes shows two main phases, depending on the source of sulfate: first sulfate is supplied by the dissolution of gypsum from the bentonite barriers, followed by a steady, low-level supply from the groundwater. Sensitivity cases demonstrate that both the organic carbon and Fe(III) oxide contents in the bentonite are critical to the corrosion evolution, by being the main electron donor for SRB activities and the major sulfide scavenger in the bentonite, respectively. The backfilled tunnel contributes little to the flux of corrosive sulfide to the canister due to the attenuation by Fe(III)-oxides/hydroxides but induces a notable flux of sulfate into the disposal hole

Eighteen years of steel–bentonite interaction in the FEBEX in situ test at the Grimsel Test Site in Switzerland

Corrosion of steel canisters containing buried high-level radioactive waste is a relevant issue for the long-term integrity of repositories. The purpose of the present study was to evaluate this issue by examining two differently corroded blocks originating from a full-scale in situ test of the FEBEX bentonite site in Switzerland. The FEBEX experiment was designed initially as a feasibility test of an engineered clay barrier system and was recently dismantled after 18 years of activity. Samples were studied by ‘spatially resolved’ and ‘bulk’ experimental methods, including Scanning Electron Microscopy, Elemental Energy Dispersive Spectroscopy (SEM-EDX), μ- Raman spectroscopy, X-ray Fluorescence (XRF), X-ray Diffraction (XRD), and 57Fe Mössbauer spectrometry, with a focus on Fe-bearing phases. In one of the blocks, corrosion of the steel liner led to diffusion of Fe into the bentonite, resulting in the formation of large (width > 140 mm) red, orange, and blue colored halos. Goethite was identified as the main corrosion product in the red and orange zones while no excess Fe2+ (compared to the unaffected bentonite) was observed there. Excess Fe2+ was found to have diffused further into the clay (in the blue zones) but its speciation could not be unambiguously clarified. The results indicate the occurrence of newly formed octahedral Fe2+ either as Fe2+ sorbed on the clay or as structural Fe2+ inside the clay (following electron transfer from sorbed Fe2+). No other indications of clay transformation or newly formed clay phases were found. The overall pattern indicates that diffusion of Fe was initiated when oxidizing conditions were still prevailing inside the bentonite block, resulting in the accumulation of Fe3+ close to the interface (up to three times the original Fe content), and continued when reducing conditions were reached, allowing deeper diffusion of Fe2+ into the clay (inducing an increase of 10– 12% of the Fe content)

Pore water chemistry of a Paleogene continental mudrock in Spain and a Jurassic marine mudrock in Switzerland: Sampling methods and geochemical interpretation

Este trabajo resume una serie de metodologías y aproximaciones desarrolladas en CIEMAT durante los últimos 10 años con el objetivo de obtener información del agua intersticial de dos formaciones arcillosas: la Opalinus Clay procedente de Suiza y una formación de edad Oligoceno Mioceno española. Ambas tienen características bastante diferentes tanto desde el punto de vista de la metodología aplicada para su estudio como del origen sedimentario en sí mismo de las dos formaciones. La arcilla Suiza se estudió a través de la participación en el experimento DI-B en el laboratorio subterráneo de Mont Terri, en Suiza, uno de cuyos objetivos fue el muestreo y análisis in situ del agua intersticial de la arcilla. Las muestras de agua se recogieron después de desarrollar equipos y metodologías para conseguir una alteración mínima de los parámetros críticos del agua de la arcilla: pH, Eh, pCO2, Fe(II) y alcalinidad. La modelización geoquímica se utilizó como herramienta para interpretar y entender los principales procesos geoquímicos que controlan la química del agua y el estado actual del sistema. En relación con la arcilla española, el artículo muestra el desarrollo de una metodología integrada para caracterizar el agua intersticial de la formación arcillosa a partir de muestras de testigos correspondientes a un sondeo, denominados S1. El estudio trata de integrar todos los datos disponibles sobre la composición del agua intersticial obtenida mediante la técnica de compresión bajo presión (squeezing) y mediante extractos acuosos, con la caracterización mineralógica y geoquímica de los testigos. La modelización geoquímica se utilizó con dos objetivos principales: para valorar la consistencia de los datos analíticos del agua intersticial y para determinar la importancia relativa de los principales procesos que gobiernan la química del agua intersticial. Específicamente, la modelización se utilizó para simular los procesos que controlan la evolución redox del sistema. Se consideró equilibrio para los minerales reactivos como la calcita, dolomita, yeso y ferrihidrita. Además, se trató la degradación de la materia orgánica y la disolución oxidativa de la pirita desde un punto de vista cinético