Calculation of appropriate oxygen concentration for corrosion inhibition of 9Cr-1Mo steel in molten lead bismuth eutectic

Komatsu, Atsushi 

In order to reduce the corrosion rate of materials in molten lead bismuth eutectic (LBE), it is important to adjust the oxygen concentration, and past reports show that the oxygen concentration is often adjusted to about 10 to 10wt%. However, it is not clearly stated what concentration is optimal, and there are some reports of severe corrosion even within this concentration range. In this study, a corrosion model considering diffusion in oxide and LBE was developed for 9Cr-1Mo steel, and the corrosion control method estimated from the corrosion model were investigated. We also tried to calculate the optimum oxygen concentration to prevent the flow blockage at the low temperature of loop environment while reducing the corrosion of 9Cr-1Mo steel in molten LBE. As a result, it was expected that the corrosion mode of 9Cr-1Mo steel in LBE could be classified into three types, dense film formation, precipitation film formation, and film dissolution, depending on the ratio of oxide film thickness to diffusion layer thickness, iron concentration in LBE, and temperature. In order to inhibit corrosion, it is important to adjust the oxygen concentration so that the conditions for dense film formation can be maintained. For this purpose, it was expected that a pre-oxidized film of more than 10m should be applied before immersion in LBE. The oxygen concentration of about 10 to 10wt% is the appropriate oxygen concentration when the oxide film has grown to some extent, and a higher oxygen concentration was expected to be required when the film is thin.