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This paper describes a multi-scale approach for the modelling of the degradation of model cement pastes using reactive transport. It specifically aims at incorporating chemistry-transport feedback results from a pore-scale approach into a continuum description. Starting from a numerical representative elementary volume of the model cement paste, which was built according to extensive experimental dedicated chacarterizations, this paper provides three separate descriptions of two different degradations: leaching and carbonation. First, 2D pore-scale simulations are performed and predict degradation depths in very good agreement with experiments. Second, 3D pore scale descriptions of how the microstructre evolves provides accurate description of the evolution of transport properties through degradation. Finally, those latter results are incorporated as a feedback law between porosity and effective diffusion coefficient into a 1D continuum approach of reactive transport. This paper provides pore-scale explanations of why reactive transport modelling has encountered mitigated success when applied to cementitious materials, especially during carbonation or degradations consisting of precipitation reactions. In addition to that, different degradation modellings are in very good agreement with experimental observations., SCOPUS: ar.j, info:eu-repo/semantics/published

Cementitious materials are widely used in the concepts of radioactive waste disposal facilities. During the lifetime of these disposals, those materials will undergo physicochemical degradations. To assess their impacts, reactive transport modelling is used. Reactive transport codes modify the transport properties based on the modelled porosity evolution by using Archie's law as a feedback between porosity and diffusive properties. These laws are not suited to cementitious materials, whose pore structure is complex and expands over a wide range of pore sizes. The ultimate goal of this research is about developing a microstructure-based feedback relation for the diffusive properties of complex porous structures such as cementitious ones. Therefore, we developed an algorithm designed to generate numerical microstructures representative of simplified cement pastes and performed an experimental campaign consisting of dedicated experiments. A random-walk algorithm is used to compute the effective diffusion coefficients of our numerical microstructures. This paper investigates the description of the initial numerical microstructure and how transport properties are sensitive to different microstructural features that can be controlled from the designed algorithm. Simulations both on the experimental microtomograph and the generated microstructures allow to show that our models are complete to describe the microstructure and diffusion transport property of simplified cementitious materials. Sensitivity analysis is also provided, whose results show that a simple feedback relation cannot properly describe these transport properties. This gives confidence in our approach and its future extension toward the description of cementitious material degradations., SCOPUS: ar.j, info:eu-repo/semantics/published

Au vu de leurs différentes propriétés, les matériaux cimentaires sont largement considérés dans les différents projets de gestion de déchets radioactifs. Leurs propriétés mécaniques, leurs faibles coefficients de transport ainsi que leur capacité à fixer les principaux radionucléides sont les principaux avantages qui en font un des meilleurs choix pour la conception des barrières ouvragées.Pour les études de sûreté, leur durabilité est capitale. Au cours de la vie d’un tel dépôt,via l’infiltration d’eau ou les interfaces chimiquement agressives avec les argiles, les différents matériaux vont subir des perturbations physicochimiques qui vont altérer leurs structures et potentiellement compromettre leurs fonctions de sûreté. L’étendue de ces perturbations, fondamentale pour l’étude de sûreté, est contrôlée par les propriétés de transport de ces matériaux.Pour modéliser proprement ces phénomènes, il faut pouvoir coupler les évolutions géochimiques des matériaux tout en évaluant le transport à travers ceux-ci. C’est le but de différents codes de transport réactif, qui utilisent une loi de rétroaction pour modifier les propriétés de transport lors d’une modification de microstructure. Le problème est qu’il n’existe pas de loi de rétroaction adaptée aux matériaux cimentaires, qui possèdent une structure poreuse complexe du nanomètre jusqu’à plusieurs micromètres. En général, des lois empiriques de type Archie sont utilisées. Toutefois, même l’utilisation de lois plus sophistiquées ne permet pas de reproduire sensiblement les évolutions liées à la structure porale. Cette loi de rétroaction est probablement la principale raison pour laquelle les résultats de simulation ont du mal à reproduire lesrésultats expérimentaux. Le but de cette thèse est de proposer une meilleure loi de rétroaction et de l’intégrer dans un code de transport réactif.Pour ce faire, trois approches complémentaires ont été mises en oeuvre. La première, expérimentale,consiste en la réalisation des matéri, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

The safeguards verification of spent nuclear fuel is one of the major concern for the safeguards community, as this material represents about 80% of all material placed under safeguards.This PhD thesis described the development of two passive non-destructive assay (NDA) techniques: the Self-Indication Neutron Resonance Densitometry (SINRD) and the Partial Defect Tester (PDET).The NDA methods were investigated with Monte Carlo simulations and the benchmark experiments for SINRD were performed at the GELINA facility of JRC-IRMM in Geel, Belgium.The results for the SINRD technique showed promising results for the direct quantification of 239Pu in spent fuel, and both techniques gave encouraging results for the detection of partial defects., Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

Proton therapy uses proton beams with energies of 70 – 230 MeV to treat cancerous tumours very effectively, while preserving surrounding healthy tissues as much as possible. During nuclear interactions of these protons with matter, secondary neutrons can be produced. These neutrons can have energies ranging up to the maximum energy of the protons and can thus be particularly difficult to attenuate. In fact, the rooms of a proton therapy facility are generally surrounded by concrete walls of at least ~2 m in thickness, in order to protect the members of the staff and the public from the stray radiation. Today, the design of the shielding walls is generally based on Monte Carlo simulations. Amongst the numerous parameters on which these simulations depend, some are difficult to control and are therefore selected in a conservative manner. Despite these conservative choices, it remains important to carry out accurate neutron dose measurements inside proton therapy facilities, in order to assess the effectiveness of the shielding and the conservativeness of the simulations. There are, however, very few studies in literature which focus on the comparison of such simulations with neutron measurements performed outside the shielding in proton therapy facilities. Moreover, the published measurements were not necessarily acquired with detectors that possess a good sensitivity to neutrons with energies above 20 MeV, while these neutrons actually give an important contribution to the total dose outside the shielding. A first part of this work was dedicated to the study of the energy response function of the WENDI-2, a rem meter that possesses a good sensitivity to neutrons of more than 20 MeV. The WENDI-2 response function was simulated using the Monte Carlo code MCNPX and validation measurements were carried out with 252Cf and AmBe sources as well as high-energy quasi-monoenergetic neutron beams. Then, WENDI-2 measurements were acquired inside and outside four rooms of the pro, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

The energy loss function (ELF) is a key parameter for the calculations of energy losses undergone by electrons in matter. It is often the only input in the calculations performed within the models based on the semi-classical dielectric response theory. Its perfect knowledge is thus of primordial importance. To evaluate the ELF, it is usual to consider as a model an expansion in Drude-Lindhard (DL) type oscillators with fixed values of the strength, width, energy and dispersion for the various oscillators. However, for materials that are characterized by a single sharp oscillator as aluminium or indium, it has been shown [Phys. Rev. B 46 (1992) 2486] that the damping parameter that corresponds in the DL model to the width of the oscillator increases for decreasing incident electron energy. To emphasize this effect, we perform in this work systematic calculation of the ELF for an indium target and for incident electron energies between 200 and 2000-eV. The ELF is determined by comparing REELS (reflection electron energy loss spectroscopy) experimental inelastic electron scattering cross sections with cross sections calculated within the semi-classical dielectric response model, which is implemented in the QUEELS-ε(k,ω)-REELS software (Quantitative analysis of Electron Energy Losses at Surfaces) [Surf. Interface Anal. 36 (2004) 824]. We also perform measurements and calculations for varying incident and exit angles of the electron, namely for angles to the surface normal between 15o and 75o, to check the validity of our results for all geometries. Our results show that the damping parameter of indium in the DL model for electron energy of 200-eV is three times larger than for energy of 2000-eV. Copyright © 2014 John Wiley & Sons, Ltd., SCOPUS: ar.j, FLWIN, info:eu-repo/semantics/published

info:eu-repo/semantics/published

Inside an IBA proton therapy centre, secondary neutrons are produced due to nuclear interactions of the proton beam with matter mainly inside the cyclotron, the beam line, the treatment nozzle and the patient. Accurate measurements of the neutron ambient dose equivalent H*(10) in such a facility require the use of a detector that has a good sensitivity for neutrons ranging from thermal energies up to 230 MeV, such as for instance the WENDI-2 detector. WENDI-2 measurements have been performed at the Westdeutsches Protonentherapiezentrum Essen, at several positions around the cyclotron room and around a gantry treatment room operated in two different beam delivery modes: Pencil Beam Scanning and Double Scattering. These measurements are compared with Monte Carlo simulation results for the neutron H*(10) obtained with MCNPX 2.5.0 and GEANT4 9.6., SCOPUS: ar.j, info:eu-repo/semantics/published

Over the last few decades, radiotherapy using high-energy proton beams over the range from 50 MeV to 250 MeV has been increasingly used and developed. Indeed, it offers the possibility to focus the dose in a very narrow area around the tumor cells. The tumor control is improved compared to radiotherapy using photon beams and the healthy cells around the tumor are not irradiated since the range of charged particles is limited. However, due to nuclear reactions of the incident charged particles in the tissue, secondary high-energy radiations, essentially photons and neutrons, are produced and irradiate the treatment room.As a consequence, thick concrete shielding walls are placed around the treatment room to ensure that other people and workers received a dose as small as possible. The dose measurement is performed with specific dosemeters such as the WENDI-II, which gives a conservative estimation of the ambient dose equivalent up to 5 GeV. The dose in working areas may also be estimated by means of numerical calculations by using simulation codes of particle transport such as the GEANT4, MCNPX, FLUKA and PHITS Monte Carlo codes.Secondary particle yields calculated with Monte Carlo codes show discrepancies when different physical models are used but are globally in good agreement with experimental data from the literature. Neutron and photon doses decrease exponentially through concrete shielding wall but the neutron dose is definitely the main component behind a wall with sufficient thickness. Shielding parameters, e.g. attenuation coefficients, vary as functions of emission angle (regarding the incident beam direction), incident proton energy, and target material and composition.The WENDI-II response functions computed by using different hadronic models show also some discrepancies. Thermal treatment of hydrogen in the polyethylene composing the detector is also of great importance to calculate the correct response function and the detector sensitivity., Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

Structural and biochemical studies of the orf12 gene product (ORF12) from the clavulanic acid (CA) biosynthesis gene cluster are described. Sequence and crystallographic analyses reveal two domains: a C-terminal penicillin-binding protein (PBP)/beta-lactamase-type fold with highest structural similarity to the class A beta-lactamases fused to an N-terminal domain with a fold similar to steroid isomerases and polyketide cyclases. The C-terminal domain of ORF12 did not show beta-lactamase or PBP activity for the substrates tested, but did show low-level esterase activity towards 3'-O-acetyl cephalosporins and a thioester substrate. Mutagenesis studies imply that Ser173, which is present in a conserved SXXK motif, acts as a nucleophile in catalysis, consistent with studies of related esterases, beta-lactamases and d-Ala carboxypeptidases. Structures of wild-type ORF12 and of catalytic residue variants were obtained in complex with and in the absence of clavulanic acid. The role of ORF12 in clavulanic acid biosynthesis is unknown, but it may be involved in the epimerization of (3S,5S)-clavaminic acid to (3R,5R)-clavulanic acid.