Influence de la corrosion du fer sur les processus d’altération du verre : approche analytique multi-échelle

Management of waste generated by the nuclear industry is a major challenge for our societies. In France, the French national radioactive waste management agency (Andra) is responsible for the implementation of the Cigéo project, an industrial geological storage center planning to use deep storage in clay medium for high level and intermediate-level long lived waste. Glass has been chosen in this project as a containment matrix for high-level radioactive waste. Understanding the long-term expected evolution of the waste package's behavior is critical for safety purposes.In order to identify the alteration mechanisms of the glass in the presence of iron from the storage container, different glass/iron/argillite systems have been altered under conditions close to those in the probable geological storage site. A coupling of post-mortem characterization techniques from the micrometric to nanometric scale allowed to characterize the systems and to identify the iron silicates formed in the glass alteration layer of the SON68 glass and in the iron corrosion products. At 50°C dioctahedral smectites of FeIII (assimilated to nontronite) are preferentially formed, while FeII-rich trioctaedric serpentines (greenalite, berthierine) are detected only at a temperature of 90°C.These nanometric phyllosilicates have a macroscopic impact on the alteration of nuclear glass. Indeed silicon/iron interactions maintain the alteration of the glass and delay the achievement of the residual rate in its alteration regime.La gestion des déchets produits par l’industrie nucléaire est un enjeu majeur de nos sociétés. En France, l’Agence nationale pour la gestion des déchets radioactifs (Andra), est chargée de la mise en œuvre du projet Cigéo, centre industriel de stockage géologique, un concept de stockage profond en milieu argileux des déchets radioactifs HA et MAVL. Dans ce concept, le verre a été choisi comme matrice de confinement pour les déchets radioactifs de haute activité et la prédiction du comportement du colis de déchet sur le long terme est l’un des éléments essentiels de sureté. Afin d’identifier les mécanismes d’altération du verre en présence de fer issu du conteneur de stockage, différents systèmes verre/fer/argilite ont été altérés dans des conditions proches du probable site de stockage géologique. Un couplage de techniques de caractérisation post-mortem de l’échelle micro à nanométrique a permis de caractériser les systèmes et d’identifier les silicates de fer qui se forment dans la couche d’altération du verre SON68 et dans les produits de corrosion du fer. A 50°C, les smectites dioctaédriques de FeIII (assimilées à de la nontronite) se forment préférentiellement, tandis que des serpentines trioctaédriques riches en FeII (greenalite, berthierine) ne sont détectées que pour une température de 90°C. Ces phyllosilicates nanométriques ont un impact macroscopique sur l’altération du verre nucléaire. En effet les interactions silicium/fer entretiennent l’altération du verre et retardent l’atteinte du régime d’altération en vitesse résiduelle

Corrosion Mitigation in Molten Salt Environments

International audienceThe aim of this paper is to present methods for corrosion mitigation in molten salt environments. The corrosion of structural materials depends directly on the redox potential of the salt. When the redox potential of the salt is higher than the standard potentials of the elements constituting the structural materials, corrosion occurs. If the reverse is true, no corrosion is observed. Herein, a methodology for calculating the theoretical potential of a molten salt is provided and compared with experimental measurements. Three ways to mitigate corrosion by modifying the salt redox potential are proposed: (i) using a soluble/soluble redox system; (ii) using a potentiostatic method; and (iii) using an amphoteric compound such as UCl3, TiCl2, or TiCl3. Immersion tests were conducted under the above conditions to validate the methodology.</jats:p

Glass/iron/claystone interactions of nuclear waste package: a multi-scale study relying on characterizations and geochemical modeling

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Nuclear waste glass/iron/clay interactions: a multi-scale study relying on characterization and geochemical modeling

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Use of nanoprobes to identify iron-silicates in a glass/iron/argillite system in deep geological disposal

International audienceThe understanding of glass alteration mechanisms in contact with iron is a major issue to study the long-term behavior of radioactive waste package in repository conditions. A glass/iron/claystone system was altered in contact with COx water at 50°C for 4.5 years in Andra's underground research laboratory in Bure, France. Multiscale and multitechnical (SEM-EDX, µRaman, STXM and TEM) characterization of the system revealed the presence of nanometric crystalline Fe(III)-rich smectite, assimilated to nontronite, in the glass alteration layer and in corrosion products. These phyllosilicates were identified by STXM using a comparative approach with a database of reference spectra obtained on iron-silicate

Influence of iron corrosion on nuclear glass alteration processes: nanoscale investigations of the iron-bearing phases

International audienceA carbon steel container including nuclear glass has been altered for 2 years in Andra's Underground Research Laboratory to simulate the behaviour of waste package. Post-mortem analyses at different scales (macro–micro–nano) have been performed to identify neoformed phases on iron corrosion products (ICP) and in the glass alteration layer (GAL). It has been shown at nanometric scale that important quantities of iron and silicon were found in the GAL and in the ICP respectively. Using a comparative approach with phyllosilicate references, STXM, at Si-K edge, suggests presence of trioctahedral species in the GAL and in ICP. Relevant fits of the STXM spectra are obtained with a Fe-rich chlorite for the nanostructured GAL, which could be formed according to chloritisation mechanism. ARTICLE HISTOR

Glass-Iron-Claystone interactions: a study relying on characterizations and geochemical modeling

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AVM nuclear glass/steel/claystone system altered by Callovo–Oxfordian poral water with and without cement–bentonite grout at 70°C

International audienceThe effect of a cement–bentonite grout material was studied through glass/steel interactions. Hence, two experimental mock-ups, consisting of a “sandwich” of four materials in contact, stainless steel/AVM glass/AVM glass/P285NH steel, were leached by Callovo–Oxfordian poral water at 70°C for 1 year. CBG material was added for one experiment, whereas the second one was CBG-free. Chemical and structural analyses (scanning electron microscopy–energy-dispersive X-ray spectroscopy, Raman), performed mainly at the AVM glass/P285NH interface, evidenced a comparable alteration with and without the CBG. Indeed, its presence did not impact the gel formation by hydrolysis/condensation mechanism. For both experiments, the glass alteration rates corresponded to $r_0^{Cox,70°C}\over 32$, highlighting a kinetic rate drop after a 1-year leaching period. However, the CBG impacted the pH solution initially buffered by the claystone, promoting precipitation of Mg/Fe-rich silicates on the gel surface. Regarding P285NH corrosion, no major difference was observed with the CBG. Steel corrosion layers in both experiments were Si-free, and the corrosion rates were similar. Therefore, after 1 year at 70°C, the CBG had a limited effect on the glass/carbon steel interactions

New insights of Auger spectroscopy for the identification of Fe-Si compounds in iron/glass corrosion systems at nanoscale

International audienceIn the context of high-level radioactive wastes (HLW) storage, long term alteration of glass and corrosion of metallic containers leads to the formation of sub-micrometric phyllosilicate phases in the iron Corrosion Product Layer (CPL). The nature of these phases, their properties (porosity, electronic, passivation…) and their spatial distribution must be identified to determine their exact role in the iron corrosion process and to efficiently predict the long-term alteration of nuclear wastes package. In this work, the capabilities of localized Auger spectroscopy, combining surface chemical determination and high spatial resolution, to characterize these phyllosilicate phases is presented. In the present context, the main challenge to overcome was the insulating character of the different compounds and samples, presenting a real disadvantage for Auger implementation. A specific experimental protocol had to be developed to enable acquiring exploitable spectra at sufficiently high resolution to obtain identifiable fingerprints. The main Si-KLL Auger transition of different types of phyllosilicates representative of those encountered in the CPL of the glass-iron systems was acquired to determine if different chemical signatures and chemical shifts could be observed in function of the structure of reference phyllosilicates phases. Indeed, the Si-KLL kinetic energy position value of the phyllosilicate increases with the structure according the following order: smectite group < chlorite group < serpentine group and different line shapes are observed. The significant contribution of the present study relies on the achievement of analyzing such insulating materials by Auger at nanometric scale using a new generation Auger nano-probe (spot size around 12 nm) without drastic preparation requirements, enabling to constitute a Si-KLL Auger data base of phyllosilicates. Thanks to this preliminary analytical approach, the Si-KLL fingerprint measured in the CPL of the glass/iron system altered in an anoxic reactor at 90 °C in synthetic Callovo-Oxfordian (COx) clay-based groundwater solution could be identified as serpentine phyllosilicate. Transmission electron microscopy (TEM) analysis was also used to characterize phyllosilicate and reinforce the AES approach identification, confirming the presence of serpentines

Influence of iron corrosion on nuclear glass alteration processes: nanoscale investigations of the iron-containing phases

International audienceSeveral strategies propose to store and confine High Level Radioactive Waste in a deep geological disposal. Andra (French National Radioactive Waste Management Agency) suggests a multi barrier system including the glass canister, a carbon steel overpack and a low permeability clay host rock to prevent borosilicate glass alteration and to limit migration of radionuclides released under the action of water. However after thousand years and resaturation of clay, water will corrode the carbon steel overpack causing the release iron ions and precipitation of iron carbonates as corrosion products. The glass matrix will alter through glass hydrolysis and release silicon in solution. Thus, neoformed Fe-Si-O phases can precipitate in the glass alteration layer (GAL) or at the outer part of the GAL and lower the concentration of Si in solution, increasing glass dissolution. Consequently identification and characterization of nanocrystallized Fe-Si-O phases is crucial for modelling the mechanism of glass alteration in contact with iron. The results presented here are obtained on samples (mix of nuclear glass and iron powder) altered in the underground Laboratory of Bure (France). Micro and Nanoscale investigations (Transmission Electron Microscopy, Scanning Transmission X-Ray Microscopy, nanoAuger electron spectroscopy) show presence of neoformed nanocristallized phases (iron silicates) inside GAL and in the iron corrosion products (ICP). Several families of structured Si-Fe-O phases are identified (e.g. smectite in ICP, chlorite and iron sulfide in GAL) according to the localization and the valence of iron in CP. Moreveor study of the provenance of silicium and iron found in phyllosilicates was carried out in mass spectroscopy (TOF-SIMS). Thereby it is possible to know the proportion of silicon and iron arising from the glass, initially substituted for 29-silicium and 5-iron, to form these silicates