The conditioning of highly active and long-lived nuclear waste should include several barriers to isolate radionuclides from the environment, during the required storage time. One of these barriers is a steel outer container that will corrode extremely slowly over several thousand years.

While field experiments continue at the Andra in the Meuse/Haute-Marne, researchers from Iramis are modelling these long-term processes based on laboratory experiments and the study of analogous archaeological parts that have been corroding for centuries. In particular, they have analyzed the corrosion of a steel model in storage conditions at Saclay, by combining several complementary techniques. These techniques include transmission electron microscopy and field emission microscopy, as well as scanning transmission X-ray microscopy.

Steel is known to corrode by forming iron carbonates that are more or less porous. However, Iramis's analyses show a submicronic layer of iron oxides (magnetite and maghemite) located between the steel and these corrosion products. The thickness of this layer varies from a few tens of nanometers to a micrometer, depending on the compactness of the clay environment. According to the study, it is this distinct interface that controls the corrosion rate of the steel.

Crédit C. Dupont/CEA