Emilien Burger

Silicate glass alteration enhanced by iron: origin and long-term implications.

Silicate glasses are used as containment matrices for deep geological disposal of nuclear waste arising from spent fuel reprocessing. Understanding the dissolution mechanisms of glasses in contact with iron, an element present in large amounts in the immediate environment (overpack, claystone, etc.) would be a major breakthrough toward predicting radionuclide release in the geosphere after disposal. Two different reacted glass-iron interfaces-a short-term nuclear system and a long-term archeological system-were examined using a multiscale and multianalytical approach including, for the first time on samples of this type, STXM under synchrotron radiation. Comparisons revealed remarkable similarities between the two systems and shed light on Fe-Si interactions, including migration of iron within a porous gel layer and precipitation of Fe-silicates that locally increase short-term glass alteration and are sustainable over the long-term.

In situ structural characterisation of nonstable phases involved in atmospheric corrosion of ferrous heritage artefacts

Abstract The prediction of very long term corrosion of iron and low alloy steel in atmospheric conditions or in hydraulic binder media is a crucial issue for the conservation and restoration of heritage artefacts. For both media, the typical iron corrosion product layers (CPL) can be described as a matrix of goethite (α-FeOOH) crossed by marblings of reactive phases: maghemite (γ-Fe2O3), ferrihydrite (Fe5HO8.4H2O), feroxyhyte (δ-FeOOH), etc. The aim of the experiments presented here is to bring new insights on the role that the maghemite could potentially play in the mechanisms of corrosion. For that purpose, electrochemical reductions have been coupled with in situ Raman microspectroscopy. These experiments enable the authors to propose a hypothesis of local mechanisms in the specific case of marblings of maghemite connected to the metallic substrate. These local mechanisms could drastically influence the global corrosion rate.

Corrosion of carbon steel components in the French high-level waste programme: evolution of disposal concept and selection of materials

ABSTRACT In France, the reference concept for the geological disposal of high-level waste (HLW) consists of horizontal micro-tunnels, containing carbon steel casing and overpacks (around a stainless steel container containing vitrified waste). The overpacks and casing will be exposed to an environment that will evolve over time: from a hot and humid atmosphere containing oxygen, to an anoxic environment saturated with water at the geothermal temperature. Lots of corrosion experiments have been performed in representative environments to study steel corrosion modes (general corrosion, pitting and crevice corrosion, stress corrosion cracking, hydrogen embrittlement…) while taking into account the influence of temperature, radiation, mechanical stresses and microorganisms. Some key results have influenced the design of the HLW disposal cell, including the carbon steel grades and dimensions of the casing and overpacks, or the addition of an alkaline grout material between the casing and the host rock. This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.