Corrosion long terme de matériaux métalliques / Long term corrosion of multimaterials containing metals
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Corrosion long terme de matériaux métalliques / Long term corrosion of multimaterials containing metals

Nanometer barrier layer identified by STXM/NEXAFS on archaeological analogues corroded in anoxic carbonated water

Plusieurs pays envisagent de développer une technologie de barrières multiples pour la sécurité du stockage des déchets nucléaires. Une question centrale est de savoir modéliser le comportement sur le long terme (soit 100 à 1000 ans) des matériaux utilisés, en particulier des containers, en acier faiblement allié, et de la matrice vitrifiée.

Dans ce cadre général, le NIMBE/LAPA cherche à mettre en évidence les mécanismes de corrosion à long terme de systèmes contenant des alliages ferreux et du verre dans les divers milieux envisagés pour le stockage profond ou les stockages provisoires (atmosphère, béton et liants hydrauliques).

La méthode est basée sur l'étude d'analogues archéologiques provenant de sites de référence sur lesquels il est possible de mesurer les paramètres environnementaux et de disposer d'un nombre d'objets suffisants pour une étude en laboratoire. Ceux-ci sont ensuite étudiés à différentes échelles de l'échelle macroscopique à celle du nanomètre. L'étude d'échantillons altérés dans des conditions contrôlées en laboratoire complète l'approche.

 


 

Several countries envisage to develop a multibarrier concept for the safe storage of nuclear wastes. The main issue is to manage to predict on the long term (i.e. 100 to 1000 years) the behaviour of the materials and especially of the low alloy steel overcontainer and its vitrified matrix, by modelling.

In that general framework, LAPA is interested to evidence long-term corrosion mechanisms of systems containing ferrous alloys and glass in various media concerned by deep storage (anoxic carbonated water) or interim storage (atmosphere, concrete and hydraulic binders).

The methodology is based on the study of archaeological analogues coming from reference sites on which it is possible to measure the environmental parameters and to sample a significant number of artefact that can be later studied in laboratory. The system is then investigated at different scales from macro to nanometer. Studying short-term altered samples in controlled conditions in the laboratory completes the approach.

 

 
#339 - Màj : 04/01/2016
Domaines Techniques
The Raman microspectrometry is an analytical device of primary importance to characterize the crystalline structure of materials. It is a complementary technique to micro X-ray diffraction. This technique is well suited to characterize and determine the distribution of the phases formed in the corrosion layers of iron or steels during very long periods in various environments. Iron oxides, oxy-hydroxides and carbonates are the main phases encountered in these systems.
Raman microspectroscopy at NIMBE/LAPA
Faits marquants scientifiques
D. Neff, P. Dillmann, L. Bellot-Gurlet*, G. Béranger**

One of the most important technological challenge of the century is the safe storage of nuclear wastes. In France, one part of the engineered barrier designed to separate the biosphere from wastes is a low alloy steel overpack. Thus, it is necessary to predict the very long term corrosion behaviour of this overpack for several centuries. For this purpose, in addition of modelling and laboratory simulating, it is necessary to look at corrosion products developed on archaeological analogues in comparable environments. A study made on iron archaeological artefacts buried in soil during several centuries is performed in the LPS.. Samples are taken on archaeological sites with the adhering soil and cross sections are made. Characterisation techniques are optical and electronic microscopes, Energy Dispersive Spectrometry coupled to Scanning Electron Microscopes, Electron Probe Micro Analyses, micro X-ray Diffraction under synchrotron radiation and micro Raman spectrometry. A specific terminology is proposed to describe the corrosion layout. The most identified corrosion layout is made of several ten micrometers zones of magnetite and/or maghemite embedded in a goethite matrix and forms in aerated soils. A corrosion mechanism is proposed in order to explain this profile. When the soil water contains more chlorine or carbonates and less dissolved oxygen some specific corrosion product appear as akaganeite, oxichlorides and siderite. * Laboratoire de Dynamique Interactions et Réactivité (LADIR), UMR 7075 CNRS - Université Pierre et Marie Curie Paris VI, 2 rue Henri Dunant, 94320 Thiais, France ** Université de Technologie de Compiègne, Laboratoire Roberval, Centre de Recherche de Royallieu, BP529, 60205 Compiègne Cedex, France

 

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