Study of Zircaloy-4 fuel cladding corrosion using ion beams - Application to long term disposal of nuclear wastes

AC

Radiation endurance in Al2O3nanoceramics

The lack of suitable materials solutions stands as a major challenge for the development of advanced nuclear systems. Most issues are related to the simultaneous action of high temperatures, corrosive environments and radiation damage. Oxide nanoceramics are a promising class of materials which may benefit from the radiation tolerance of nanomaterials and the chemical compatibility of ceramics with many highly corrosive environments. Here, using thin films as a model system, we provide new insights into the radiation tolerance of oxide nanoceramics exposed to increasing damage levels at 600 °C-namely 20, 40 and 150 displacements per atom. Specifically, we investigate the evolution of the structural features, the mechanical properties, and the response to impact loading of Al2O3 thin films. Initially, the thin films contain a homogeneous dispersion of nanocrystals in an amorphous matrix. Irradiation induces crystallization of the amorphous phase, followed by grain growth. Crystallization brings along an enhancement of hardness, while grain growth induces softening according to the Hall-Petch effect. During grain growth, the excess mechanical energy is dissipated by twinning. The main energy dissipation mechanisms available upon impact loading are lattice plasticity and localized amorphization. These mechanisms are available in the irradiated material, but not in the as-deposited films

IBA and SIMS coupling to study glass alteration mechanisms

International audienceAlkali-alumin o-boro silicate glasses have been synthesized by melting the stoichiometric corresponding powder mixtures and heating at 1100 degrees C in a platinum crucible. Electron microprobe analyses were then carried out in order to determine their initial composition. Glass samples were submitted to static aqueous leaching tests in deionized water during 1 month (surface/ratio = 0. 3 cm(-1)) at temperature of 96 degrees C. The leachates were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The leached samples were then characterized by ion beam analytical (IBA) methods: Rutherford backscattering and elastic recoil spectrometries (RBS and ERDA), proton-induced X-ray or gamma ray emission (PIXE and PIGE) and secondary ion mass spectrometry (SIMS). The role of the presence of one or several contained transition elements (Fe, Mo, and Nd) and the effect of their respective contents on the chemical durability of alkali-borosilicate glasses were investigated. This work outlines the fact that a competition may occur between congruent and selective dissolution. Both surface hydration thickness and mobile element depletion amplitude cannot be considered as the unique reliable glass durability indicators. (c) 2007 Published by Elsevier B.V

APPLICATION DES METHODES NUCLEAIRES D'ANALYSE AUX MESURES NON DESTRUCTIVES DE PROFILS DE CONCENTRATION ENGENDRES DANS LA REGION SUPERFICIELLE DES VERRES PAR LA LIXIVIATION AQUEUSE

Après une description sommaire des techniques nucléaires d'analyse basées sur l'observation directe de réactions résonnantes et sur la rétrodiffusion élastique de particules chargées, des exemples de profils de concentration se rapportant à des verres lixiviés en milieu aqueux sont présentés.Nuclear analytical techniques based on direct observation of resonant reaction and charged particle backscattering are briefly described. Few depth profile examples concerning leached glasses are shown

Dissolution of LnYSiAlO glass (Ln=La or Ce) in aqueous media. I. Influence of the pH on hydrolysis mechanisms and kinetics

ACEStatic leaching tests have been performed on LnYSiAlO glasses (Ln=Lanthanide: La or Ce) that are considered as potential matrices for the specific immobilization of minor actinides. The influence of the nature of the rare earth on alteration mechanisms and kinetics is studied by synthesizing two analogous compositions with lanthanum or cerium. Four series of leaching tests have been carried out for different initial pH values ranged between 1 and 13 (HNO$_3$ and NaOH dilute media, $T=90^\circ$ and $S/V$=0.06 cm$^{−1}$). For acid pH around 1–2, Al and Y + Ln are released and the formation of a non-protective Si-rich layer (a few μm thick) at the glass/solution interface is observed. On the other hand, this family of glass presents a strong chemical resistance for slightly acid and basic pH media. This property is linked to the formation of a surface protective layer that includes Al or Ln + Y hydroxides (or oxides) depending on the Ln nature and the solubility of these compounds at the considered pH. In the case of LaYSiAlO glass where only La(III) is stable, the solubility of these secondary phases is the parameter probably controlling the dissolution through the formation of a very thin passivating surface layer. This property is quite interesting in the perspective of a storage in clay or granitic medium, where flowing natural waters present a slightly basic pH. In the case of CeY glass, the possible oxidation of Ce(III) to Ce(IV) during leaching leads to a thicker surface layer, probably CeO$_2$. At the same time, an increase of the initially near-neutral pH is observed, and a preferential release of Al and Si elements occurs

Ion beam irradiation of Sn films deposited on YSZ(100)

International audienceThis paper reports the formation processes of crystalline Sn nanostructured films grown under ultra high vacuum conditions on monocrystalline yttria-stabilized zirconia (YSZ) substrates with (10 0) orientation. The microstructure of the films was analyzed using SEM and X-ray diffraction. Evaporation of Sit films yields crystallographically well-defined metallic islands of different shapes depending on the substrate temperature. The overall growth mechanism appears to follow the Stranski-Krastanov type. Irradiation of deposited films was performed at room temperature with 4 MeV Au2+ ions at a fluence of 10(15) cm(-2) to induce material decomposition and aggregation of host atoms. X-ray diffraction and Rutherford backscattering spectrometry (RBS) experiments conducted on Sn films deposited on YSZ(l 00) prior to and after irradiation demonstrate that ion irradiation drives a structural phase transformation for Sri and Zr-rich compositions. The microstructural evolution upon ion irradiation was also examined by cross-sectional transmission electron microscopy (TEM). (C) 2008 Published by Elsevier B.V

Characterization of the alteration products formed at the surface of LaYSiAlO and CeYSiAlO glasses using ERDA and RBS techniques

ACELeaching tests have been performed on LnYSiAlO glasses (Ln = La or Ce) that are considered as potential matrices for the specific immobilization of minor actinides. Elastic recoil detection analysis (ERDA) performed on leached samples indicated a superficial hydration of LaYSiAlO glass of about 100–150 nm. This hydrated layer is (Al, Y)-enriched according to SEM-EDS analysis, suggesting the formation of hydroxide (or hydroxycarbonates) compounds including these two elements. This process leads to a very efficient passivation of the material due to the low solubility of Al and Y hydroxides (and hydroxycarbonates) species in near neutral media, even when the solution is rapidly replenished is dynamic leaching experiments. Rutherford Backscattering Spectrometry elemental mapping revealed very localized and significantly Y-enriched deposits at the surface of the sample after leaching. This could be the sign of heterogeneities already present on the pristine glass. These may be correlated with the weak solubility of yttrium (and rare earth) elements in silicate matrices (Y + Ln initial content in the glass ≈11 at.%). In the case of CeYSiAlO glass, a thin layer was formed on the solid after leaching. The simulation of the corresponding RBS spectra showed a surface (Y, Ce)-enrichment and (Al, Si)-depletion in both cases. This could be explained by the oxidation of trivalent cerium initially present in the glass structure during leaching. This might be explained by the low solubility of Ce(IV)-compounds (CeO2 and/or Ce(OH)4) in solution leading to an enrichment of this element at the glass/solution interface, to form a mixture of amorphous CeO2 and Y(OH)3, as confirmed by XPS and XRD experiments

An attempt to correlate ion irradiation behaviour and chemical durability of titanate- and zirconate-based ceramics

International audienceTitanate and zirconate samples from perovskite and pyrochlore families have been submitted to low energy heavy ion irradiation in order to pre-damage their crystalline structure. Samples irradiated below or near their amorphisation threshold were then leached in deionised water at 90 degrees C in static mode while samples irradiated above their amorphisation threshold were leached at 100 degrees C in dynamic mode. Below the amorphisation threshold, only slight effects of the pre-irradiation have been found on the chemical durability of titanate and zirconate from the perovskite family. Above the amorphisation threshold, perovskite surfaces exhibit a stronger hydration and an increase of the growth kinetics of secondary phases identified as TiOOH and ZrOOH compounds mainly. The pre-irradiated pyrochlore (Nd(2)Zr(2)O(7)) exhibits both a higher hydration degree and a higher Nd-Zr surface co-enrichment due to the destabilization of their network by the pre-irradiation. (C) 2008 Elsevier B.V. All rights reserved

Diffusion and retention of helium in titanium carbide

International audienceThe knowledge of helium migration in TiC is an important issue due to its possible use as fuel coating in fission reactors and as first wall material coating in fusion reactors. Helium release measurements and diffusion coefficient calculations of helium in polycrystalline TiC have been carried out in the temperature range (1000–1600 °C) for the time period of 2 h. Polished bars of TiC were implanted with 3 MeV $^3$He$^+$ ions in normal incidence at a dose of 5 × 10$^{20}$ at./m$^2$ at room temperature. Helium depth profile was measured at each step using the $^3$He(d, p$_0$)$^4$He nuclear reaction by varying the incident deuteron energy from 900 to 1800 keV. Effective diffusion coefficients vary from 4.20 × 10$^{−18}$ to 2.59 × 10$^{−17}$ m$^2$ s$^{−1}$ and activation energy values obtained are in the range 0.8–2.5 eV. Due to scarce availability of stoichiometric TiC, challenges in this study came from native vacancies present in the samples. The helium distribution and its release were affected by the presence of grain boundaries. He is considered to undergo two distinct populations into the sample and different values of diffusion coefficient have been determined for each population