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Bore T.,Ecole Normale Superieure de Cachan | Bore T.,University of Queensland | Wagner N.,Bauhaus University Weimar | Lesoille S.D.,French National Radioactive Waste Management Agency Andra | And 4 more authors.
Sensors (Switzerland) | Year: 2016

Broadband electromagnetic frequency or time domain sensor techniques present high potential for quantitative water content monitoring in porous media. Prior to in situ application, the impact of the relationship between the broadband electromagnetic properties of the porous material (clay-rock) and the water content on the frequency or time domain sensor response is required. For this purpose, dielectric properties of intact clay rock samples experimental determined in the frequency range from 1 MHz to 10 GHz were used as input data in 3-D numerical frequency domain finite element field calculations to model the one port broadband frequency or time domain transfer function for a three rods based sensor embedded in the clay-rock. The sensor response in terms of the reflection factor was analyzed in time domain with classical travel time analysis in combination with an empirical model according to Topp equation, as well as the theoretical Lichtenecker and Rother model (LRM) to estimate the volumetric water content. The mixture equation considering the appropriate porosity of the investigated material provide a practical and efficient approach for water content estimation based on classical travel time analysis with the onset-method. The inflection method is not recommended for water content estimation in electrical dispersive and absorptive material. Moreover, the results clearly indicate that effects due to coupling of the sensor to the material cannot be neglected. Coupling problems caused by an air gap lead to dramatic effects on water content estimation, even for submillimeter gaps. Thus, the quantitative determination of the in situ water content requires careful sensor installation in order to reach a perfect probe clay rock coupling. © 2016 by the authors; licensee MDPI, Basel, Switzerland. Source


Bore T.,Ecole Normale Superieure de Cachan | Wagner N.,Bauhaus University Weimar | Delepine-Lesoille S.,French National Radioactive Waste Management Agency Andra | Taillade F.,Electricite de France | And 3 more authors.
SAS 2015 - 2015 IEEE Sensors Applications Symposium, Proceedings | Year: 2015

The use of electromagnetic sensors such as Time Domain Reflectometry (TDR) probes has gained increasing importance for long term monitoring of the water content in radioactive waste repositories. TDR probes are sensitive to changes in electromagnetic properties of the surrounding material, a clay rock in our case. Prior to the in situ application, it is mandatory to have an accurate relationship between the electromagnetic properties of the intact host clay rock and the water content. For this purpose, the dielectric properties of intact clay rock samples were systematically studied at frequencies from 1 MHz to 10 GHz with network analyzer technique in combination with coaxial transmission line cells. Samples were conditioned to achieve a water saturation range from 16 % to nearly saturation. The relaxation behavior was quantified based on a generalized fractional relaxation model under consideration of an apparent direct current conductivity assuming three relaxation processes: a high-frequency water process and two interfacial processes which are related to interactions between the aqueous pore solution and mineral particles (adsorbed/hydrated water relaxation, counter ion relaxation and Maxwell-Wagner effects). In a second step, these data are introduced in 3-D numerical frequency domain finite element field calculations to model the one port broadband frequency or time domain transfer function for a three rode based TDR-probe embedded in the clay rock. The results are analyzed with classical travel time analysis (onset/inflection) which under/overestimates the value of the permittivity compared to effective permittivity at 1 GHz. Indeed, apparent permittivity contains not only the water-content contribution but also effects due to water-mineral interaction processes. The results demonstrate the capabilities of a combined TD/FD analysis procedure for the monitoring of physical and chemical properties of materials with high frequency electromagnetic sensor techniques. © 2015 IEEE. Source


Jia Y.,Wuhan University | Jia Y.,Lille University of Science and Technology | Bian H.B.,French National Center for Scientific Research | Duveau G.,Lille University of Science and Technology | Poutrel A.,French National Radioactive Waste Management Agency Andra
Computers and Geotechnics | Year: 2016

In this paper, the effects of steel corrosion on the THM response of the geological barrier is studied by simulating a disposal tunnel of high-level radioactive wastes (HLW). The simulation is performed by using a coupled THM finite element code and two different constitutive models: a visco-elastoplastic model for the geological barrier and a von-Mises type model for the steel barriers. The corrosion effects are numerically simulated by a decrease of mechanical properties of steel and a volumetric expansion related to corrosion products. The detailed geometries of engineered barriers and their internal void spaces are incorporated into the numerical simulation. The evolutions of temperature, liquid pressure, displacement, and stress fields in the geological barrier (called the Callovo-Oxfordian claystone) are analyzed. The numerical results exhibit that the influence of steel corrosion on the THM response of the claystone is limited in the near field of disposal tunnel, especially for the displacement and stress fields in the claystone. However, the evolutions of temperature, liquid pressure and plastic zone in the claystone are not disturbed by the corrosion process of steel barriers and are controlled essentially by its THM properties. © 2015 Elsevier Ltd. Source


Gorny J.,Lille University of Science and Technology | Billon G.,Lille University of Science and Technology | Lesven L.,Lille University of Science and Technology | Dumoulin D.,Lille University of Science and Technology | And 2 more authors.
Science of the Total Environment | Year: 2015

The fate of arsenic - a redox sensitive metalloid - in surface sediments is closely linked to early diagenetic processes. The review presents the main redox mechanisms and final products of As that have been evidenced over the last years. Oxidation of organic matter and concomitant reduction of oxidants by bacterial activity result in redox transformations of As species. The evolution of the sediment reactivity will also induce secondary abiotic reactions like complexation/de-complexation, sorption, precipitation/dissolution and biotic reactions that could, for instance, lead to the detoxification of some As species. Overall, abiotic redox reactions that govern the speciation of As mostly involve manganese (hydr)-oxides and reduced sulfur species produced by the sulfate-reducing bacteria. Bacterial activity is also responsible for the inter-conversion between As(V) and As(III), as well as for the production of methylated arsenic species. In surficial sediments, sorption processes also control the fate of inorganic As(V), through the formation of inner sphere complexes with iron (hydr)-oxides, that are biologically reduced in buried sediment. Arsenic species can also be bound to organic matter, either directly to functional groups or indirectly through metal complexes. Finally, even if the role of reduced sulfur species in the cycling of arsenic in sediments has been evidenced, some of the transformations remain hypothetical and deserve further investigation. © 2014 Elsevier B.V. Source


El Hajj H.,CNRS Laboratory of Subatomic Physics and Associated Technologies | Abdelouas A.,CNRS Laboratory of Subatomic Physics and Associated Technologies | El Mendili Y.,CNRS Laboratory of Subatomic Physics and Associated Technologies | Karakurt G.,CNRS Laboratory of Subatomic Physics and Associated Technologies | And 2 more authors.
Corrosion Science | Year: 2013

We investigated sequential aerobic and anaerobic microbiologically induced corrosion of carbon steel to simulate deep geological disposal conditions. Under limited oxygen supply, lepidocrocite and magnetite corrosion products formed on the steel coupon, while under continuous oxygen supply, a mixture of lepidocrocite, maghemite and magnetite was identified. Upon oxygen consumption and establishment of sulphidogenic conditions, due to sulphate-reducing bacteria activity, all these oxides disappeared via transformation into pyrrhotite. Corrosion rate of steel in direct anaerobic cultures was higher than that of steel initially corroded in aerobic condition, suggesting a protective role of corrosion product layer formed under sequential aerobic-anaerobic conditions. © 2013 Elsevier Ltd. Source

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