Corrosion of carbon steel in physically-constrained locations in HLNW isolation containers

A bounding 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 a supercontainer proposed for storage of high level nuclear waste. This model allows us to estimate the corrosion potential, rates of general corrosion of the overpack, hydrogen pressure, water saturation, and the porosity of the rust as corrosion proceeds along the corrosion evolutionary path. It is shown that, at lower values of water saturation S < 0.2-0.3, complete exhaustion of water within the annulus in predicted, completely protecting the overpack from further general corrosion. At higher values of water saturation the overpack is also predicted to be protected by the compression of the outer layer against the concrete buffer and hence by the reduction in porosity of the rust to form an impervious barrier.