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Figures showing the measurements before applying the calibration curve

Invited Talk 1; International audience; The H2MEMS project aims at developing and optimizing hydrogen sensors based on resonant MEMS for detection of hydrogen release in radioactive waste disposal facility. The principle adopted is based on measuring physical properties of the gas (mass density, viscosity, sound velocity and sound absorption) without requiring any sensitive layer. For this purpose, resonant microcantilevers and CMUT were used.

Nuclear Waste Disposal (NWD) programs mainly focus on deep geological storage, as this is the most appropriate strategy for ensuring the long-term safety of people and environment. Cigeo is a future deep NWD facility for high-level and intermediate level long-lived radioactive waste, to be built in France, at 500 m depth within the clayey Callovo-Oxfordian formation (COx). High-activity radioactive waste will be placed in linings made of carbon steel API 5L X65. The space between the steel and the COx will be filled with a basic cemento-bentonic material (FS10B, but can still evolve), and which allow a better control of corrosion by maintaining the steel passivation. The cementeous media, without agitation, separates into two phases: a clear supernatant one, rich in sulfides, and a compact lower phase, hardening over time, and whose conductivity decreases significantly over the 90 days of experiment. Initially of gray color, the lower cement phase takes after a few days a green tint, attributed to the progressive anaerobiosis of the media and the presence of polysulfides in the blast furnace slag used in CEM III/A cement production. A specific methodology consisting of several loops of various electrochemical techniques around the Open Circuit Potential (OCP) (-700 mV/ESH using Ag/AgCl as solid reference) is used to determine the corrosion rate of the steel by calculating the polarization resistance. The Stern-Geary parameter found while fitting Buttler-Volmer relation with VaOCP data, allows us to obtain the corrosion current values. The combination of Linear Polarization and Electrochemical Impedance Spectroscopy (EIS) leads to understand the mechanims under which the corrosion occurs. It is then found to be limited by the diffusion of protons H + in absence of oxygen in a very basic media (pH >12). The current densities start very low (

Cigeo is a future deep Nuclear Waste Disposal (NWD) facility for high-level and intermediate level long-lived radioactive waste, to be built in France, at 500 m depth within the clayey Callovo-Oxfordian formation (COx). Deep knowledge of the mechanisms and kinetics of corrosion occurring at the surface of tubings made of API 5L X65 carbon steel in contact with pore water of COx, is essential for a reversible NWD management of the site. This work aims to determine by various electrochemical techniques, the corrosion kinetics of the carbon steel X65 in contact with COx pore water flowing continuously through a multi-parameter probe (MPP), an innovative device for long-term monitoring, placed at 490 m depth for more than 156 days into a gallery of the Underground Research Laboratory of Andra at Bure, France.A triplet, (X65 electrode - Ag/AgCl solid reference electrode - Pt counter electrode), is electrochemically monitored. Ag/AgCl(s) and Pt electrodes showed stability and robustness for over 156 days. Electrochemical Impedance Spectroscopy (EIS) measurements performed at Open Circuit Potential (OCP) of X65, allowed to identify a rather classic equivalent circuit model in water and showed that the corrosion is limited by the H+ reduction. Tafel plots and Voltammetric measurements around OCP and gave a Gary Stern parameter close to 15 mV, which used to determine the X65 corrosion current densities from the linear polarization resistances (LPR) obtained also by EIS. From 5 μA/cm² in the first hours, the current density decreases until day 5 to reach less than 1 μA/cm². The EIS analysis (Nyquist plot) revealed the appearance during this period of an increasing second loop at low frequencies, corresponding to a protective deposit on the steel surface. The current density then increases from day 5 to reach 10 μA/cm² (i.e. 120 μm/year on day 25). This period corresponds to the disappearance of the low-frequency capacitive loop in Nyquist plot, meaning that the deposit no longer protects the steel from corrosion.

International audience; This paper summarizes the work performed in Task 3.6, Reliability and Qualification of components, of the EU H2020 project Modern2020. It synthezises progress made by eight expert organisations on a common multi-stage methodology for qualifying monitoring components (MC) of the measurement chain (sensor, connecting cable and/or wireless system/controller) at a Deep Geological Repository (DGR). This study was reported as document D3.6 [1] in the Modern2020 project and results from a multi-stage analysis including: i) the study of transferable experience gained from the energy and space fields, ii) the feed back of long-term and demonstration experiments operating in conditions close to those expected in repositories at Underground Research Laboratories (URLs) or at large mock-up, iii) the initiatives for the development of a qualification process for selecting and testing the monitoring components and at last, iv) the proposal for a global protocol appropriate to all monitoring contexts.

International audience; We present innovative electrochemical probes for the monitoring of pH and redox potential in pore water in near-field rocks of a future deep geological radioactive waste repository at 500 m depth within the clayey Callovian-Oxfordian (COx) formation. The conceived experimental setup assembles two multi-parameter probes (MPPs), used together throughout two series of several months duration measurements in situ into the underground research laboratory of Andra at Bure, France. The two MPPs, connected in series, were up-flow fed with actual pore water of COx formation during several with a very low flowrate. Each MPP is composed of different individual probes containing the following: two monocrystalline antimony electrodes for pH sensing; eight AgCl/Ag-based reference or Cl − selective electrodes; four Ag 2 S/Ag-based reference or S 2− selective electrodes; eight platinum electrodes; two gold electrodes; two glassy-carbon electrodes; two ruthenium and two inox 316 electrodes, for redox potential measurements. The Open Circuit Potential (OCP) measurements of the developed sensors under different conditions and in quasi-actual conditions were compared to conventional reference electrode and pH electrodes in terms of performance, reliability and robustness and allowed to create calibration curves. Conductivity measurements, carried out along MPPs, will not be presented here. Overall, the conceived bundle of electrodes as designed works reliably during a timescale that is promising for monitoring the COx formation during its envisaged use for hosting a nuclear waste repository.

International audience; The demonstration of monitoring technologies in repository like conditions is hence essential to assess the quality of engineering design and determine safety strategies. This study offers a summary of the design and field operations that have led to the construction of a dedicated in situ test called “Long Term Rock Buffer Monitoring” (LTRBM) experiment which aims at testing new monitoring technologies developed in and outside the Modern2020 project. A preliminary evaluation of the new and innovative technologies, including new sensors and wireless transmitting devices is also proposed. The design setup allows an engineered barrier composed by a 4 meter long bentonite buffer and 2 meter long cement plug to be saturated by synthetic water composition in equilibrium with the COx claystone (pH = 7.2), through 5 independent hydration mats. The new sensors and wireless devices were placed in and around the engineered barrier to monitor chemical parameters, pressure and saturation variations during the buffer hydration. Though a large majority of the sensors are working and react immediately to the evolving bentonite structure, some of the new prototypes have failed to measure or transmit data from the buffer. The failure of these prototypes is generally connected to handling and preparation issues prior to their installation. The first 6 months of monitoring has demonstrated that LTRBM experiment offers a reliable, cost effective and reproducible setup to assess the performance of a wide range of monitoring technologies.

Geophysical Electrical Resistivity Tomography (ERT) is a promising measurement technique for non-intrusive monitoring of Engineered Barrier System (EBS) during the operational phase of geological disposal of high-level radioactive waste. Electrical resistivity is sensitive to water content and temperature, which are the key variables characterising the response of the EBS. In order to assess the technology readiness level of the ERT technique for EBS operational monitoring, a field demonstrator has been developed at the URL in Tournemire (France) within the project 'Modern 2020'. Preliminary ERT surveys were carried out in January and November 2017 to establish the background resistivity of the experimental area and assess the quality of electrode installation and survey protocols. Results of the surveys confirmed that the resistivity of the host rock in the demonstrator area is quite homogeneous and lower than 100Ωm in accordance with independent measurements carried out in previous campaigns. In addition, the lesson learned from the blank tests allowed identifying key requirements for effective ERT measurements. These include the need for a 3D electrode configuration, bespoke measurement protocols designed on the basis of sensitivity analysis of geometric factors, and collection of reciprocal data for enhanced data quality control.

International audience

International audience

The analysis of optical and acoustic properties of optical fibers is required for accurate Brillouin gain spectrum (BGS) determination. We present a full modal-analysis of the guided optical and acoustic modes based on a two-dimensional finite-element method (2D-FEM) for BGS calculation using COMSOL Multiphysics. We believe that this method will be helpful in analyzing and designing special fibers for applications, such as fiber amplifiers with significant SBS (Stimulated Brillouin Scattering) suppression or Brillouin-based fibersensors. The model is adapted for BGS evaluation of any single mode fiber (in term of optical mode) based on its profile, namely its geometry, and its doping composition. Compared to standard multi-layer methods limited to axially-symmetric fibers [1], the 2D-FEM analysis enables the BGS computation even for more complicated geometries, such as PANDA polarization-maintaining fiber where the optical index and the material stress are azimuthally dependant. The results of numerical modeling have shown good agreement with measured Brillouin spectra for different types of silica fibers. Examples are given for a standard GeO2-doped core fiber (standard fiber for telecommunication applications), Fluor-doped cladding fiber (acoustic anti-waveguide) and PANDA fiber.

169 pages; The influence of the electrode nature on the performance of semiconducting metal oxide based gas sensors is recognized and experimentally proven. Here, for the first time we are providing clear spectroscopic evidence (DRIFTS) for the influence of the electrodes nature (Pt and Au) on the surface chemistry associated to CO detection with SnO2 thick film sensors. Our results show that the nature and concentration of the CO reaction intermediates (carbonates and carboxylates) depend on the presence and nature of the electrodes. Moreover, Thermodesorption measurements prove that the influence of the electrodes nature plays a key role on oxygen adsorption at the SnO2 surface. The result will be discussed in order to be useful for basic understanding of gas sensors.; L'influence de la nature des électrodes sur les performances des capteurs de gaz à base d'oxyde métallique semiconducteur sont reconnu et prouvé expérimentalement. Ici, pour la première fois nous fournissons une mise en évidence par spectroscopie infrarouge (DRIFTS) de l'influence de la nature d'électrodes (Pt et Au) sur la chimie de surface lors de la détection de CO aux sur couche épaisse de SnO2. Nos résultats montrent que la nature et la concentration des intermédiaires de réaction de CO (les carbonates et carboxylates) dépendent de la présence et de la nature des électrodes. De plus, les mesures en thermodésorption prouvent que l'influence de la nature des électrodes joue un rôle clé sur l'adsorption d'oxygène à la surface SnO2. Ces résultats sont discutés au sein d'un modèle empirique.

The influence of the electrode nature on the performance of semiconducting metal oxide based gas sensors is recognized and experimentally proven. Here, for the first time we are providing clear spectroscopic evidence (DRIFTS) for the influence of the electrodes nature (Pt and Au) on the surface chemistry associated to CO detection with SnO2 thick film sensors. Our results show that the nature and concentration of the CO reaction intermediates (carbonates and carboxylates) depend on the presence and nature of the electrodes. Moreover, Thermodesorption measurements prove that the influence of the electrodes nature plays a key role on oxygen adsorption at the SnO2 surface. The result will be discuss in order to be useful for basic understanding of gas sensors. L'influence de la nature d'électrode sur les performances de capteur de gaz à base d’oxyde métallique semiconducteur est reconnu et prouvé expérimentalement. Ici, pour la première fois nous fournissons une mise en évidence par spectroscopie infrarouge (DRIFTS) de l'influence de la nature d'électrodes (Pt et Au) sur la chimie de surface lors de la détection de CO aux sur couche épaisse de SnO2. Nos résultats montrent que la nature et la concentration des intermédiaires de réaction de CO (les carbonates et carboxylates) dépendent de la présence et de la nature des électrodes. De plus, les mesures en Thermodesorption prouvent que l'influence de la nature d'électrodes joue un rôle clé sur l'adsorption d'oxygène à la surface SnO2. Ces résultats sont discutés au sein d’un modèle empirique.

The influence of the electrode nature on the performance of semiconducting metal oxide based gas sensors is recognized and experimentally proven. Here, for the first time we are providing clear spectroscopic evidence (DRIFTS) for the influence of the electrodes nature (Pt and Au) on the surface chemistry associated to CO detection with SnO2 thick film sensors. Our results show that the nature and concentration of the CO reaction intermediates (carbonates and carboxylates) depend on the presence and nature of the electrodes. Moreover, Thermodesorption measurements prove that the influence of the electrodes nature plays a key role on oxygen adsorption at the SnO2 surface. The result will be discussed in order to be useful for basic understanding of gas sensors., L'influence de la nature des électrodes sur les performances des capteurs de gaz à base d'oxyde métallique semiconducteur sont reconnu et prouvé expérimentalement. Ici, pour la première fois nous fournissons une mise en évidence par spectroscopie infrarouge (DRIFTS) de l'influence de la nature d'électrodes (Pt et Au) sur la chimie de surface lors de la détection de CO aux sur couche épaisse de SnO2. Nos résultats montrent que la nature et la concentration des intermédiaires de réaction de CO (les carbonates et carboxylates) dépendent de la présence et de la nature des électrodes. De plus, les mesures en thermodésorption prouvent que l'influence de la nature des électrodes joue un rôle clé sur l'adsorption d'oxygène à la surface SnO2. Ces résultats sont discutés au sein d'un modèle empirique.