Investigation of dental amalgam electrode behaviour for the long term monitoring of nuclear waste disposals

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Intercomparison of Ta and Ti solid-electrodes for pH measurements under oxic and anoxic conditions in reconstituted waters of a future nuclear waste disposal

International audienceIn France, the deep geological disposal has been chosen to manage long-lived high and middle activity nuclear waste. This project is supervised by " the Agence National pour la Gestion des Déchets Radioactif" (ANDRA-French national radioactive waste management agency). An underground research laboratory (URL), dedicated to host-rock properties characterization was built at approximately-490m depth in the Callovo-Oxfordian geological formation (COx), which is a potential candidate for nuclear waste disposal. Based on this overall strategy, Andra has analysed the technical requirements that must be met by adapted monitoring equipment. First, these must be able to provide information on key THMCR (Thermal-Hydraulic-Mechanical-Chemical and Radiological) processes, to provide a three-dimensional image of its behaviour and thus to understand the underground installation functioning, in particular the cell interactions with the near-field. This study aims to develop innovative all-solid-state electrodes made of iridium (Ir), ruthenium (Ru), tantalum (Ta), titanium (Ti), tungsten (W), niobium (Nb) and a tin-lead alloy (Sn/Pb), for pH measurement. Moreover, the potentiometric response of these electrodes is mainly based on Metal Oxide (M x O y)/Metal (M) equilibriums, which make them react to changes of oxygen partial pressures. For now, the antimony electrode (Sb) showed excellent results regarding the measure of pH under oxic and anoxic conditions. Nevertheless, it is necessary to multiply the electrode materials considered for pH measurements, for preventing a dysfunction of electrodes which could occur over time. By multiplying the electrode materials for pH measurement, we indirectly increase, firstly, the measurement reliability by giving the possibility to inter-compare the potentiometric responses of the set of the electrodes dedicated to pH, and secondly, the monitoring duration, in the case of electrode surface alterations, which could be caused by variations of the physical and chemical parameters within the nuclear waste repository. In other words, this would provide alternatives electrode materials for pH measurements, in prevention to possible electrode surface alterations. Thus, the influence of pH from 5 to 13, on the potentiometric responses of the several electrodes was investigated by means of pH buffers solutions or by continuous and regulated addition of H 2 SO 4 or NaOH, under both oxic (exposed at air) and anoxic conditions (in glove box: 99% N 2 , 1% CO 2 and [O 2 ] < 2 ppm, 25°C). Titanium (Ti) and tantalum (Ta) electrodes showed a potentiometric linear response to pH variations, as shown on figures 1 and 2. In absence of oxygen, the Ti electrode showed a linear response to pH (from 5.8 to 11), close to the theory. After pH 11, a drop of potential is observed. In presence of oxygen, the response to pH is linear but further to the theory. In the same way, the potentiometric behaviour of the Ta electrode to pH variations is linear, but much more sensitive under anoxic conditions

Multi-Parametric Devices with Innovative Solid Electrodes for Long-Term Monitoring of pH and Redox-Potential of the actual pore water of COx formation in a future Nuclear Waste Repository

International audienceWe 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

Multi-parametric device with innovative all-solid-state electrodes for long term monitoring of pH, redox and conductivity in reconstituted anaerobic water of a future nuclear waste disposal

International audienceNuclear waste disposal are being installed in deep excavated rock formations in some places in Europe to isolate and store radioactive waste. To ensure long term safety and to provide reliable data for future decision making process, it is necessary to implement long-term monitoring sensors. Thereby, robust, sustainable, reliable and autonomous sensors (no-maintenance required) have to be developed to measure the most important physical and chemical parameters.This study aims at developing and optimizing a multi-parametric device composed of all-solid-state electrodes for the long term monitoring of pH, redox potential (ORP) and ionic conductivity. The multi-parametric device consists of a limited number of inert or/and weakly alterable electrodes, allowing auto-controlled and redundant open circuit potential differences measurements in semi-continuous way.Based upon the reversible interfacial redox processes involving H+, Sb2O3/Sb system has been regarded among the most promising technologies to be devoted to the monitoring of pH into the underground components of nuclear disposal due to its physical and chemical stability, with regards to temperature, pressure and aggressive environments1. For redox potential measurements, platinum wires (Pt-Ir alloy; 90-10%) were selected among the “inert” conductive material presenting physical and chemical stability properties. All-Solid-state AgCl/Agcoated/Ag was selected for the development of non-conventional reference electrodes since its potential only depends on Cl- concentration and because the on-site Cl- concentration should remain relatively stable on the long term2.Performance and reliability were examined by potentiometric measurements in various pH buffer solutions at 25°C, under atmospheric conditions as well as in an “oxygen free” gloves box (99% N2, 1% CO2 and [O2]<2ppm). Investigations were limited in pH, ranging from 5.5 to 13.5, close to those encountered in the environment of the nuclear repositories. Robustness was then investigated over six months in a synthetic solution whose composition in major elements and pH was representative of the Callovo-Oxfordian (COx) pore water. For conductivity measurements, both platinum wires as well as AgCl/Agcoated-Ag electrodes were used. The Galvanostatic Electrochemical Impedance Spectroscopy (GEIS) was used, which consisted in applying a known alternating current (AC) between the two most distant electrodes and to measure the induced potential between two other electrodes. The Sb-electrode proved to be reliable for pH measurements. In the absence of any redox couple, except O2/H2O, the platinum electrode showed a linear potentiometric response to pH variations. The all-solid-state AgCl/Agcoated-Ag electrode showed a stable potentiometric response over several months even when subjected to pH variations. According to our results, the long-term monitoring of pH and ORP via the multi-parametric device is feasible. Further investigations are in progress regarding: (i) the influence of redox species such as S(VI)/S(II) or Fe(III)/Fe(II) and (ii) corrosion rates of each electrode materials in order to estimate electrodes lifetime and therefore of the device

A Multi-Parametric Device with Innovative Solid Electrodes for Long-Term Monitoring of pH, Redox-Potential and Conductivity in a Nuclear Waste Repository

International audienc

DexRay: A Simple, yet Effective Deep Learning Approach to Android Malware Detection Based on Image Representation of Bytecode

Computer vision has witnessed several advances in recent years, with unprecedented performance provided by deep representation learning research. Image formats thus appear attractive to other fields such as malware detection, where deep learning on images alleviates the need for comprehensively hand-crafted features generalising to different malware variants. We postulate that this research direction could become the next frontier in Android malware detection, and therefore requires a clear roadmap to ensure that new approaches indeed bring novel contributions. We contribute with a first building block by developing and assessing a baseline pipeline for image-based malware detection with straightforward steps. We propose DexRay, which converts the bytecode of the app DEX files into grey-scale “vector” images and feeds them to a 1-dimensional Convolutional Neural Network model. We view DexRay as foundational due to the exceedingly basic nature of the design choices, allowing to infer what could be a minimal performance that can be obtained with image-based learning in malware detection. The performance of DexRay evaluated on over 158k apps demonstrates that, while simple, our approach is effective with a high detection rate(F1-score= 0.96). Finally, we investigate the impact of time decay and image-resizing on the performance of DexRay and assess its resilience to obfuscation. This work-in-progress paper contributes to the domain of Deep Learning based Malware detection by providing a sound, simple, yet effective approach (with available artefacts) that can be the basis to scope the many profound questions that will need to be investigated to fully develop this domain

JuCify: A Step Towards Android Code Unification for Enhanced Static Analysis

International audienceNative code is now commonplace within Android app packages where it co-exists and interacts with Dex bytecode through the Java Native Interface to deliver rich app functionalities. Yet, state-of-the-art static analysis approaches have mostly overlooked the presence of such native code, which, however, may implement some key sensitive, or even malicious, parts of the app behavior. This limitation of the state of the art is a severe threat to validity in a large range of static analyses that do not have a complete view of the executable code in apps. To address this issue, we propose a new advance in the ambitious research direction of building a unified model of all code in Android apps. The JuCify approach presented in this paper is a significant step towards such a model, where we extract and merge call graphs of native code and bytecode to make the final model readily-usable by a common Android analysis framework: in our implementation, JuCify builds on the Soot internal intermediate representation. We performed empirical investigations to highlight how, without the unified model, a significant amount of Java methods called from the native code are "unreachable" in apps' call-graphs, both in goodware and malware. Using JuCify, we were able to enable static analyzers to reveal cases where malware relied on native code to hide invocation of payment library code or of other sensitive code in the Android framework. Additionally, JuCify's model enables state-of-the-art tools to achieve better precision and recall in detecting data leaks through native code. Finally, we show that by using JuCify we can find sensitive data leaks that pass through native code

JuCify: A Step Towards Android Code Unification for Enhanced Static Analysis

Native code is now commonplace within Android app packages where it co-exists and interacts with Dex bytecode through the Java Native Interface to deliver rich app functionalities. Yet, state-of-the-art static analysis approaches have mostly overlooked the presence of such native code, which, however, may implement some key sensitive, or even malicious, parts of the app behavior. This limitation of the state of the art is a severe threat to validity in a large range of static analyses that do not have a complete view of the executable code in apps. To address this issue, we propose a new advance in the ambitious research direction of building a unified model of all code in Android apps. The JuCify approach presented in this paper is a significant step towards such a model, where we extract and merge call graphs of native code and bytecode to make the final model readily-usable by a common Android analysis framework: in our implementation, JuCify builds on the Soot internal intermediate representation. We performed empirical investigations to highlight how, without the unified model, a significant amount of Java methods called from the native code are ``unreachable'' in apps' call-graphs, both in goodware and malware. Using JuCify, we were able to enable static analyzers to reveal cases where malware relied on native code to hide invocation of payment library code or of other sensitive code in the Android framework. Additionally, JuCify's model enables state-of-the-art tools to achieve better precision and recall in detecting data leaks through native code. Finally, we show that by using JuCify we can find sensitive data leaks that pass through native code