Modeling of carbon steel corrosion under oxygen depleted environment

Shibata, Toshio*; Watanabe, Masatoshi; Taniguchi, Naoki ; Shimizu, Akihiko*

In Japan, High-level radioactive waste produced by reprocessing spent fuels has been planned to be fixed in a glass solid body which is further enclosed in metal canisters. Carbon steel is the candidate material for the canisters, because the corrosion rate of carbon steel is known to be as low as 10 microm per year at an deep underground site. Corrosion rate data of the candidate steel have been accumulated in the laboratory and fields, and the corrosion rate of steel in this environment has been found to be almost 10 microm per year at the initial stage, which decreases gradually with time. In this study, a rational corrosion model assuming the diffusion of HO molecule through the precipitated corrosion film has been developed under oxygen depleted environment. The model also assumes that the dissolution of precipitated FeO film is controlled by mass transfer process through adjusting diffusion layer in the solution. Digital simulation based on the corrosion model was found well to simulate the observed corrosion rate change with time at various pHs and to predict a low and steady state corrosion rate after long time exposure.