The kinetics of uniform oxide formation and its relationship to radiation effects on Zircaloy-2

Specimens of Zircaloy-2 plate were irradiated with 2 MeV proton at 350°C up to total dose of 1 dpa (displacement per atom). Uniform corrosion tests, at 400°C in 10.3 MPa steam, were performed in an autoclave. It was found that the radiation enhanced the uniform corrosion rate. The oxide morphology was studied by cross-sectional transmission electron microscopy. The oxide consists of two types of oxide layer, one formed in the early stage which is equiaxial, the other formed later which is columnar. Comparing the as-received and irradiated specimens, it was found that the difference in oxide thickness depends on the development of columnar oxide layer. The effect of radiation on the oxide morphology is considered to be the same in the oxide nucleation stage, but produces a significant difference in the oxide growth stage. It is believed that the stress induced the oxide morphology evolution, and had some effects on the corrosion behavior. A corrosion model is proposed to explain these results.