Research on Corrosion of Carbon Steel Simulating Environment inside Containment Vessel of Fukushima Daiichi Nuclear Power Plant

Abstract

Coolant circulation and injection is currently conducted into the containment vessel (PCV) of Fukushima Daiichi Nuclear Power Plant (1F) Units 1-3. In order to maintain the integrity of the PCV over a long period of time until the decommissioning of the plant, it is necessary to predict the corrosion behavior of carbon steel, which is the main structural material of the PCV, and in particular to examine the factors that may accelerate corrosion. The carbon steel used in the PCV is exposed to alternating gas and liquid environments near the gas-liquid interface (gas-liquid alternating environment). Carbon steel is covered with a thin liquid film near the gas-liquid interface, and the corrosion rate of steel is accelerated when there is a thin water film on the steel surface compared to that in an aqueous solution. Therefore, excessive wall thinning due to corrosion is a concern for carbon steel near the gas-liquid interface inside the 1F PCV compared to in water.

In this study, we developed a rotating corrosion test apparatus that simulates the gas-liquid interface at 1F and investigated the corrosion rate of carbon steel in air-liquid alternating environment. We have found that the corrosion rate of carbon steel in an air-liquid alternating environment is accelerated more than four times faster than that in a constant liquid environment due to the liquid film formed on the steel surface. Furthermore, cross-sectional observation and analysis of corrosion products on carbon steel after corrosion tests revealed that corrosion is accelerated because oxygen reduction reactions always occur in areas with high oxygen supply just below the liquid film due to the formation of multilayered iron rust layers on carbon steel in the gas-liquid alternating environment.

Keywords

Corrosion, Carbon Steel, Water Film, Iron Rust, Dissolved Oxygen

Publications

• K.Otani, F.Ueno, C.Kato, Effect of Oxygen Concentration on Corrosion Rate of Carbon Steel in Air/solution Alternating Condition, Zairyo-to-Kankyo, 71 (2021) pp 71-76 (2021). (in Japanese)
• K.Otani, C.Kato, Corrosion of Carbon Steel in the Simulated Air/Solution Interface Environment, Zairyo-to-Kankyo, 70, pp 815-820 (2020). (in Japanese)
• K.Otani, T.Tsukada, F.Ueno, C.Kato, Effect of Seawater Components on Corrosion Rate of Steel in Air/solution Alternating Condition, Zairyo-to-Kankyo, 69, pp 246-252 (2020). (in Japanese)
• K.Otani, T.Tsukada, F.Ueno, Analysis for the Mechanism of Accelerated Corrosion on Low Alloy Steel in Air-solution Alternating Condition, Zairyo-to-Kankyo, 68, pp 205-211 (2019) (in Japanese)