Chimie de l'uranium(VI) à l'interface solution/minéraux (quartz et hydroxyde d'aluminium) : expériences et caractérisations spectroscopiques

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Synchrotron X-Rays for Microstructural Investigations of Advanced Reactor Materials

X-rays from synchrotron beamlines provide a powerful tool for materials analysis in circumstances where long-term materials degradation under complex loading conditions (e.g., temperature, irradiation, and stress) becomes important. This may occur for advanced gas cooled reactors. Synchrotron X-rays can help to improve lifetime assessments by providing a more in-depth understanding of microstructural damage. This article summarizes results of X-ray absorption fine spectrum analysis and X-ray magnetic circular dichroism synchrotron techniques. They were employed to evaluate various microstructural features, which are important in understanding the lifetime of materials exposed to extreme conditions. Dispersoid strengthening by yttria particles, conditions that produce nanocrystal Zircaloy, and the role of magnetism on the stability of ferritic steels were taken as example

Uranium (VI) chemistry at the interface solution/minerals (quartz and aluminium hydroxyde),experiments and spectroscopic investigations of the uranyl surface species

This study deals with the understanding of the uranyl chemistry at the 0.1 M NaNO3 solution/mineral (quartz and aluminium hydroxide) interface. The aims are:(i) to identify and to characterize the different uranyl surface species (mononuclear, polynuclearPas de résum

Uranium (VI) chemistry at the interface solution/minerals (quartz and aluminium hydroxyde),experiments and spectroscopic investigations of the uranyl surface species

Pas de résuméThis study deals with the understanding of the uranyl chemistry at the 0.1 M NaNO3 solution/mineral (quartz and aluminium hydroxide) interface. The aims are:(i) to identify and to characterize the different uranyl surface species (mononuclear, polynuclear complexes and/or precipitates...), i.e. the coordination environments of sorbed/precipitated uranyl ions, by using X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) and time-resolved laser-induced fluorescence spectroscopy (TRLFS), and;(ii) to investigate the influence of pH, initial uranyl aqueous concentration and hydroxyl ligand concentration on the uranyl surface speciation.Our study on the speciation of uranyl ions at the quartz surface (i) confirms the formation of uranyl polynuclear/oligomers on quartz from moderate (1 mol/m2) to high (26 mol/m2) uranyl surface concentrations and (ii) show that theses polynuclear species coexist with uranyl mononuclear surface species over a pH range 5-8.5 and a wide range of initial uranyl concentration of the solutions (10-100 M). The uranyl concentration of these surface species depends on pH and on the initial uranyl aqueous concentration.Hydrate (surface-) precipitates and/or adsorbed polynuclear species and monomeric uranyl surface complexes are formed on aluminium hydroxide. Uranyl mononuclear complexes are predominant at acidic pH, as well as uranyl in solution or on the surface. Besides mononuclear species, precipitates and/or adsorbed polynuclear species are predominantly formed at neutral pH values on aluminium hydroxide. A main contribution of our investigations is that precipitation and/or adsorption of polynuclear species seem to occur at low uranyl surface concentrations (0.01-0.4 mol/m2). The uranyl surface speciation is mainly dependent on the pH and the aluminol ligand concentration

Chimie de l'uranium (VI) à l'interface solution/minéraux (quartz et hydroxyde d'aluminium) (expériences et caractérisations spectroscopiques)

This study deals with the understanding of the uranyl chemistry at the 0.1 M NaNO3 solution/mineral (quartz and aluminium hydroxide) interface. The aims are:(i) to identify and to characterize the different uranyl surface species (mononuclear, polynuclear complexes and/or precipitates...), i.e. the coordination environments of sorbed/precipitated uranyl ions, by using X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) and time-resolved laser-induced fluorescence spectroscopy (TRLFS), and;(ii) to investigate the influence of pH, initial uranyl aqueous concentration and hydroxyl ligand concentration on the uranyl surface speciation.Our study on the speciation of uranyl ions at the quartz surface (i) confirms the formation of uranyl polynuclear/oligomers on quartz from moderate (1 mol/m2) to high (26 mol/m2) uranyl surface concentrations and (ii) show that theses polynuclear species coexist with uranyl mononuclear surface species over a pH range 5-8.5 and a wide range of initial uranyl concentration of the solutions (10-100 M). The uranyl concentration of these surface species depends on pH and on the initial uranyl aqueous concentration.Hydrate (surface-) precipitates and/or adsorbed polynuclear species and monomeric uranyl surface complexes are formed on aluminium hydroxide. Uranyl mononuclear complexes are predominant at acidic pH, as well as uranyl in solution or on the surface. Besides mononuclear species, precipitates and/or adsorbed polynuclear species are predominantly formed at neutral pH values on aluminium hydroxide. A main contribution of our investigations is that precipitation and/or adsorption of polynuclear species seem to occur at low uranyl surface concentrations (0.01-0.4 mol/m2). The uranyl surface speciation is mainly dependent on the pH and the aluminol ligand concentration.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Condition Monitoring of High Temperature Components With Sub-Sized Samples

Advanced nuclear plants are designed for long-term operation in quite demanding environments. Limited operation experience with the materials used in such plants necessitate a reliable assessment of damage and residual life of components. Non-destructive condition monitoring of damage is difficult, if not impossible for many materials. Periodic investigation of small samples taken from well defined locations in the plant could provide an attractive tool for damage assessments. This paper will discuss possibilities of using very small samples taken from plant locations for complementary condition monitoring. Techniques such as micro/nano-indentation, micropillar compression, micro bending, small punch and thin strip testing can be used for the determination of local mechanical properties. Advanced preparation techniques such as focused ion beam (FIB) allow the preparation of samples from these small volumes for micro-structural analyses with transmission electron microscope (TEM) and advanced X-ray synchrotron techniques. Modeling techniques (e.g. dislocation dynamics DD) can provide a quantitative link between microstructure and mechanical properties. Using examples from ferritic oxide dispersion strengthened materials the DD approach is highlighted to understand component life assessments

Synchrotron X-Rays for Microstructural Investigations of Advanced Reactor Materials

X-rays from synchrotron beamlines provide a powerful tool for materials analysis in circumstances where long-term materials degradation under complex loading conditions (e.g., temperature, irradiation, and stress) becomes important. This may occur for advanced gas cooled reactors. Synchrotron X-rays can help to improve lifetime assessments by providing a more in-depth understanding of microstructural damage. This article summarizes results of X-ray absorption fine spectrum analysis and X-ray magnetic circular dichroism synchrotron techniques. They were employed to evaluate various microstructural features, which are important in understanding the lifetime of materials exposed to extreme conditions. Dispersoid strengthening by yttria particles, conditions that produce nanocrystal Zircaloy, and the role of magnetism on the stability of ferritic steels were taken as examples

Synchrotron Light Techniques for the Investigation of Advanced Nuclear Reactor Structural Materials

In the frame of the Generation IV initiative, different structural material candidates are investigated at the Paul Scherrer Institute. These are oxide dispersion strengthened (ODS) steels, intermetallic materials and ceramic composite materials. The response of the material to different potential loads (irradiation, temperature …) is addressed in a multi-scale approach, both, modelling wise and also experimentally. The investigation of each scale delivers at least a qualitative understanding of possibly evolving damage in the material and also delivers a validation of the corresponding scale on the modelling side. From the experimental side, the lower end of the scale, the atomistic and structural level, can be investigated by conventional techniques, as for example transmission electron microscopy (TEM) and X-ray diffraction (XRD). However, the use of synchrotron radiation techniques offers an ideal, complementary way to investigate the material structure and other properties. This paper presents applications in the field of the ODS research, where the structural behaviour of the nanoscopic dispersoids can selectively be investigated, although only being present with roughly 5 wt % in the matrix. A study showing the structural behaviour of these oxide particles as a function of irradiation illustrates the potential of the extended X-ray absorption fine structure (EXAFS) technique. Using X-ray magnetic circular dichroism (XMCD), which is a difference-signal of two X-ray absorption spectra recorded for positive and negative helicities of the beam, the magnetic structure and some magnetic parameters, can be resolved. An example shows, how this can be applied to understand (Fe,Cr) systems, which is the base alloy of the investigated ODS steel. The results deliver an important crosscheck for modelling. Beside the presentation of these techniques, this paper shows how beamline techniques can serve nuclear research, with possibly activated materials. At the Paul Scherrer Institute, a sample holder for highly active materials has been developed, and has already served for EXAFS measurements at the Swiss Light Source (SLS). The set-up of this sample holder is briefly presented here

Irradiation effects in helium implanted silicon carbide measured by X-ray absorption spectrometry

Silicon carbide (SiC) is investigated as a possible structural material for future nuclear power plants. It is utilized as fibre and/or as matrix in ceramic composite materials. The fibre reinforcement is necessary to provide the required ductility. In this work, the behaviour of pure SiC under irradiation by He implantation is studied. Samples are investigated by means of the extended X-ray absorption fine structure (EXAFS) spectroscopy, performed at the Si K-edge. The Fourier transforms of the EXAFS data indicate a decrease of the Si–Si bond related shells around the absorbing Si. The possible damage features are discussed and the three most probable ones for the irradiation conditions are selected for future modelling work