Effect of Water Chemistry on the Performance of Alloy 800H in Supercritical Water-cooled Reactor

In order to study the influence of water chemistry factors such as temperature and dissolved oxygen on the service performance of cladding materials in supercritical water environment, and to find out the water chemistry control policy of supercritical water-cooled reactor, Alloy 800H was used as the experimental material in this paper, and the corrosion weight gain and slow strain rate tensile curve of the material in supercritical water under different temperature and water chemistry conditions were measured. Increasing the temperature would accelerate the corrosion rate of Alloy 800H, and the corrosion activation energy was about 159 kJ/mol. Increasing the temperature from 550℃ to 650℃, the yield strength of the material did not change significantly, which was about 175 MPa. However, the ratio of yield strength over tensile strength decreased significantly, showing an obvious softness trend of the material. At 650℃, raising the dissolved oxygen concentration from 0 μg·kg^–1 to 500 μg·kg^–1 resulted in an increase of corrosion weight gain of about 30%, but the water chemistry control method using hydrazine deoxygenation could reduce the corrosion rate of Alloy 800H. The dissolved oxygen concentration did not have a significant effect on the results of slow strain rate tensile testing, mainly because the stress corrosion failure of the material in supercritical water environment is dominated by creep process. The results indicate that appropriate controlling of temperature and dissolved oxygen in supercritical water environment can be helpful to reduce the corrosion rate of Alloy 800H and maintain its mechanical properties.