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Deciphering the non-linear impact of Al on chemical durability of silicate glass
No full textInternational audienceThe role of Al in aluminosilicate glasses remains not completely understood; at low concentration, Al increases the hydrolysis resistance, whereas at high concentration, an opposite effect is observed. To understand the origin of this phenomenon at the atomic level, we performed many Molecular Dynamics simulations through the potential mean force (PMF) method in silicate and aluminosilicate glasses to estimate the activation barriers and correlate them with the glass local structural features. Simulations have been validated by experimental studies that revealed Al is very easy to dissociate, but increases the resistance of glass alteration by significantly increasing the Si strength and glass network connectivity. In contrast, at a much larger Al concentration, preferential dissolution of Al weakens the silicate network because of weak bonds percolation, and so the glass resistance becomes very poor. Through the PMF method, we observed the activation barrier for dissociating bonds around Al to be 0.46eV, which is significantly less than for Si in pure silicate (1.22eV) and aluminosilicate glass (1.34eV). Structural investigation revealed that Si with Al as second neighbour are characterized by significantly higher activation energies than in pure silicate glass
Alpha and cluster decays of superheavy elements and 2p radioactivity of medium nuclei
No full textInternational audienceThe alpha decay, the cluster radioactivity and the heavy particle emission half-lives of known and some still unknown superheavy nuclei have been investigated within the original Generalized Liquid Drop Model and analytic formulas. The Q value has been calculated mainly from the recent NUBASE2020 tables. The agreement between the experimental data and the theoretical predictions of the alpha decay half-lives of the superheavy nuclei is correct and some predictions are provided for unknown nuclei. For some emissions of heavy particles by superheavy nuclei the half-life is comparable to the alpha decay half-lives or even smaller. The 76−80Zn, 78Ga, 72,74−76Cu, 69,71Ni and 47K nuclei seem to be the best probable candidates at an emission by superheavy nuclei, their daughter nuclei being the 205,206Hg, 206,207Tl, 208Pb, 209,210Bi, 211Po and 210At nuclei. The GLDM allows to reproduce roughly the very sparse data on 2p radioactivity
Deciphering the non-linear impact of Al on chemical durability of silicate glass
No full textInternational audienceThe role of Al in aluminosilicate glasses remains somewhat a mystery: at low concentrations, it increases the resistance to hydrolysis of the glass, whereas at high concentrations an opposite effect is observed. To understand the origin of the phenomenon on a fundamental atomistic scale, we performed 577 MD simulations and applied potential mean force (PMF) calculations to estimate the activation barriers for hydrolysis and to statistically correlate them with local structural features of the glass. Models of pure silicate and aluminosilicate glasses are constructed and investigated. PMF simulation results are further validated by the experimental measurements and revealed that Al is very easy to dissociate, but it also increases the glass chemical durability through significantly increasing both the strength of Si and network connectivity of the glass. In contrast, at high Al concentration, preferential dissolution of Al weakens the silicate network, which it supposes to strengthen, and so the glass resistance becomes poor. Through PMF calculations, we evaluated the activation barriers for dissociating bonds around Al as 0.49Â eV, which is less than a half of the energy to dissociate bonds around Si in pure silicate (1.22Â eV) and around Si in aluminosilicate glass (1.34Â eV), all these energy differences being statistically significant. Molecular structural level investigation revealed that Si with Al as a second neighbor in the glass network has a significantly higher activation energy for dissociation than Si in pure silicate glass. The proposed approach opens the way to the development of quantitative predictive models of glass durability
Atomistic Computer Modeling of Hydrocalumite As an Adsorbent for Radioactive Anions from Aqueous Solutions
No full textInternational audienceResults are presented from atomistic computer modeling of hydrocalumite (cement AFm-phase) with Cl- and I- anions in the interlayer space as a potential adsorbent of radionuclides Cl-36, I-129, Cs-137. Properties of the crystals themselves and the interaction between aqueous solutions of CsCl and CsI and surfaces of crystalline phases are studied. It is shown the adsorption of Cl- is stronger than that of I- on surfaces of hydrocalumite, which can be explained by the difference in ionic radii of hydrated anions
Fundamental Physics in the Gravitational-Wave Era
No full textInternational audienceRecording a GW […] has never been a big motivation for LIGO, the motivation has always been to open a new window to the Universe.—Kip Thorne (BBC interview, 2016)The landmark detection of gravitati..
Optimisation of the chemical oxidation reduction process (CORD) on surrogate stainless steel in regards to its efficiency and secondary wastes
No full textInternational audienceNuclear Power is a decarbonated technology of electrical energy generation. Using nuclear energy as a power source is currently considered as the best option in the fight against climate change. But the radioactive waste generated from nuclear power plants and their related facilities are matter of concern. Though the high level and intermediate level activity wastes are contained in small volumes (≤10%), significant volumes of lower activity wastes are generated. Metallic wastes are a major component of these radioactive wastes with about 500,000 tons expected in France alone, including 130,000 tons from steam generators. Majority of these metals are made of Stainless steel 316 alloy or Inconel 600. Under the effect of the primary circuit thermal-hydraulic constraints and irradiation, these the resulting corrosion products may be activated when close to the fuel, and be transported throughout the circuit. These products can be deposited on the surface of other metal components, causing contamination of the latter. The contamination can be adsorbed on the surface but can also diffuse in the oxide layers and sub-surface. The oxide layer is composed of an inner layer of Cr oxide under a layer of Ni and Fe oxide. Chemical decontamination is preferred due to the possibility of decontamination of difficult geometries and tube bends. In order to decontaminate these materials, it is important to dissolve the oxide layers chemically and a few micrometers of base metal where it could have diffused. An existing chemical method used to treat these materials is studied in this article, Chemical Oxidation Reduction Decontamination (CORD). Surrogate steel samples were prepared using high temperature induction heating and water vapour after sample preparation and cleaning. The oxide layer was characterised before treatment of the samples in the batch method at different concentrations and its effects are observed on the dissolution of the oxide layers. A protocol is being developed for the treatment of secondary waste effluents by multi-stage precipitation with a goal to reduce the total waste volumes and thus the volumes of ion exchange resins that would otherwise be needed
First Results of PEPITES, A New Transparent Profiler Based on Secondary Electrons Emission for Charged Particle Beams
No full textInternational audienceThe PEPITES project* consists of a brand new operational prototype of an ultra-thin, radiation-resistant profiler capable of continuous operation on mid-energy (O(100 MeV)) charged particle accelerators. Secondary electron emission (SEE) is used for the signal because it only requires a small amount of material (10 nm); very linear, it also offers good dynamics. The lateral beam profile is sampled using segmented electrodes, constructed by thin film methods. Gold strips, as thin as the electrical conductivity allows (~ 50 nm), are deposited on an insulating substrate as thin as possible. While crossing the gold, the beam ejects the electrons by SEE, the current thus formed in each strip allows the sampling. SEE was characterized at ARRONAX with 68 MeV proton beams and at medical energies at CPO**. Electrodes were subjected to doses of up to 10⁹ Gy without showing significant degradation. A demonstrator with dedicated electronics (CEA) is installed at ARRONAX and will be used routinely with proton beams of 17-68 MeV for intensities of 100fA to 100nA. An overview of the design and first measurements will be presented, and system performances will be assessed
Thermalisation dynamique dans les collisions d’ions lourds
No full textUltrarelativistic heavy-ion collisions at the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC) provide a hot and ultra-dense form of matter composed of deconfined quarks and gluons, named Quark-Gluon Plasma (QGP). Different models like EPOS and PHSD allow to study the space-time evolution of such heavy-ion collisions. Their dynamics is complicated; hence, various stages should be considered. The first is the primary scattering which defines to a large extent the matter distribution in the phase-space. The second stage concerns the evolution of the partonic system until the system is sufficiently dilute to hadronize. The EPOSi+PHSDe approach is introduced in this thesis, in which the EPOS model is used to determine the initial distribution of matter (partons/hadrons). This part is referred to as EPOSi. Then PHSD is employed to simulate the evolution of the matter in a non-equilibrium transport approach, referred to as PHSDe. The coupling of the two approaches is non-trivial and not straight-forward, and is discussed in detail in this manuscript. Comparing the three models, EPOS, EPOSi+PHSDe, and PHSD, interesting results find concerning their respective space-time evolutions. The results demonstrate considerably different behavior in terms of radial expansion, especially asymmetric expansion, indicating that these three models will provide different results concerning key observables. To confirm this, we study the "bulk matter observables" ( pT/mT spectra, y/ƞ distribution, v2/3/4) for Au-Au collisions at 200 GeV/A. We also investigate the Electromagnetic probes compared to the PHSD approach.Les collisions d'ions lourds ultra-relativistes au Collisionneur d'Ions Lourds Relativistes (RHIC) et au Grand Collisionneur de Hadrons (LHC) créent une forme de matière chaude et ultra-dense de quarks et gluons déconfinés, appelée Plasma de Quarks et de Gluons (PQG). Différents modèles, tels que EPOS et PHSD, permettent d'étudier l'évolution spatio-temporelle de ces collisions. La dynamique de ces collisions étant très sophistiquée, différentes étapes doivent être considérées. La première correspond aux interactions primaires, qui définit en grande partie la distribution de matière dans l'espace des phases. La deuxième étape est appelée phase partonique, durant laquelle le système évolue jusqu'à être assez dilué pour hadroniser. L'approche EPOSi+PHSDe est introduite dans cette thèse, dans laquelle la distribution initiale de matière (partons/hadrons) est déterminée grâce à EPOS, étape désignée par EPOSi. Puis, PHSD est employé pour simuler l'évolution de la matière par une approche hors-équilibre, ce à quoi réfère PHSDe. Le couplage non-trivial de ces deux approches est discuté en détail dans ce manuscrit. En comparant les trois modèles EPOS, EPOSi+PHSDe et PHSD, des résultats intéressants ont déjà été obtenus concernant les évolutions spatio-temporelles qu'ils utilisent respectivement. Nous présentons l'étude d'observables de la "matière brute" (spectres pT / mT, distributions en y / η, v2/3/4), ainsi que des sondes électromagnétiques, pour des collisions Au-Au à 200 GeV/A. La comparaison des résultats obtenus pour ces observables clés, entre les trois modèles, reflète notamment des comportements considérablement différents en terme d'expansion radiale, en particulier pour l'expansion asymmétrique