Evaluation of pH and redox conditions in subsurface disposal system for assessing influence of metal corrosion

Abstract

The properties of metal corrosion, such as the corrosion rate and corrosion expansion rate, are key factors for assessing the long term performance of the subsurface disposal system. In this study, transient changes in pH were first simulated using a finite difference computer code. In the second step, the consumption times of the residual oxygen in the facility after the backfill were calculated. Finally, the supply of dissolved oxygen in the groundwater to the engineered barrier and the corrosion amount resulting from it were estimated. A high pH of around 12·5 would persist at least for 105 years inside the low permeability layer (LPL). In addition, the results suggest that the rate of oxygen supply in the form of dissolved oxygen in the groundwater was very small due to the restriction of mass transport by the LPL and the low diffusivity layer. Thus, the environment in which aerobic corrosion extremely limited was found to be of long duration. This strongly suggests that, for assessing the long term performance of the engineered barrier system, anaerobic corrosion will have to be evaluated carefully.