Corrosion of Iron in Physically-Constrained Locations

A model has been developed to calculate the impact of the porous, outer layer of the passive film on the corrosion rate of the carbon steel overpack and on the structural integrity of the concrete in the annulus of the super container of the Belgian High Level Nuclear Waste (HLNW) disposal concept. Because the corrosion product occupies 2 – 6.5 times the volume of the iron from which it forms the development of the outer layer in the confined space between the carbon steel overpack and the concrete will result in the compression of the outer layer and a concomitant decrease in the porosity. If the porosity decreases to a sufficiently low value, the growth of the outer layer ceases and further corrosion is prevented. If the thickness of the corroded layer exceeds a critical value, the concrete will crack, because of the poor strength of cementations materials under tensile loading.