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Corrosion models predict the behavior of radioactive waste stored at depth

​Using an approach combining experimentation, characterization and multi-scale modeling, researchers from Iramis and their partners from the Direction des énergies and Andra have studied the corrosion of glass and metal in particular conditions of radioactive waste storage.

Published on 3 February 2021

In a deep disposal center such as Cigéo, in Meuse/Haute-Marne, high level, long-lived radioactive waste (spent fuel) will be isolated from its environment by a series of successive barriers: the vitreous matrix in which it is trapped, a container, an over-container and a metal liner, and finally the Callovo-Oxfordian argillite of the site (Cox). Between the liner and the argillite, an alkaline "annular space filler" (ASFM) may be added to slow the corrosion rate of the steel by providing a basic pH.

How can the joint weathering of glass and metal in waste packages be predicted over millennia (2,000 years for metal and 100,000 years for glass)?  To find out, Iramis researchers are carrying out experimental simulations with multi-scale (from millimetre to nanometre) characterisations and modelling, using the knowledge they have acquired by studying archaeological corrosion analogues.

In a first parametric study on the specific role of silicates in argillite, they studied the corrosion of two steels, ferritoperlitic and ferritic.  After one month, they observed the spontaneous formation of a nanostructured interfacial layer of magnetite (Fe3O4).  This layer is made up of nanometric grains that give it interesting diffusion barrier properties for corrosive aqueous species.

A second, more global experiment aimed at determining the influence on glass corrosion of a "cementitious grout" between the lining of the storage cell and the Cox argillite (MREA). The results show that the corrosion facies are identical, with or without filler material, and that the thicknesses of the weathering layers are similar.

About fifteen different techniques were used to determine the morphology, chemical composition, structure and physical properties of the alteration layers formed.

These two series of experiments illustrate the diversity of the studies carried out to optimize the protocol for the burial of radioactive waste, and the importance of the knowledge and expertise drawn from the study of ancient materials altered by time.

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