The accelerated corrosion of carbon steel in air-solution alternating condition

摘要

In Fukushima Daiichi nuclear power station, cooling water is constantly injected into the reactor pressure vessels (RPVs) for cooling the fuel debris after the severe accidents in March 2011. Inner components of the primary containment vessels (PCVs) was observed by remote-controlled robots and the observation showed that carbon steels of the PCVs wall above the contaminated water level was exposed to an air-solution alternating condition. In the present study, an alternating corrosion test of carbon steel which simulated the air-solution alternating condition was carried out. The surface observations after the test showed that the rust layer formed on the steel after the tests in the alternating condition was thicker than that of the steel rotated always in solution. The corrosion rate of carbon steel in the alternating condition was more than three times larger than that of the steel rotated always in solution. A thin water film was confirmed on the steel when the specimen exposed to the air during the tests. This suggests that the accelerated corrosion of the steel in the alternating condition would be caused by the thin water film on the steel during the tests.