The Oxygen and Hydrogen Diffusion Behavior in Cr-Coating by Density Functional Theory

In a pressurized water reactor, the corrosion chemical reaction between zirconium alloy cladding and water will adversely affect the mechanical properties of the cladding, thus limiting the service life of the fuel elements. In order to slow down the oxidation rate of the cladding and prevent the risk of hydrogen explosion, a conceptual design of accident tolerant fuel was proposed. Chromium metal has excellent corrosion and oxidation resistance, and has been widely used as cladding coating in the field of nuclear power. At present, the micro-mechanism of corrosion and oxidation resistance of chromium coating at high temperature is not clear, so it is urgent to carry out relevant research. In this paper, the diffusion mechanism of oxygen and hydrogen in chromium crystals has been investigated on the electronic scale by using the first principles method. Studies have shown that oxygen occupies the most stable position in the octahedral interstitial site, and hydrogen tends to occupy the tetrahedral interstitial site. The solubility of hydrogen is much lower than that of oxygen. The negative dissolution energy of oxygen in the interstitial site indicates that there is a strong mutual attraction between oxygen and the first nearest neighbor chromium. Further, the reaction-diffusion paths and migration energy barriers of oxygen and hydrogen are calculated by elastic band method. The oxygen diffuses from the tetrahedral interstitial site to the first nearest tetrahedral interstitial site along the reaction path, exhibiting a migration migration energy barrier of 0.79eV. Simultaneously, it also migrates from the tetrahedral interstitial site to the first near octahedral interstitial site with a migration energy barrier of .65eV. These findings suggest a preferential diffusion pathway from tetrahedral to octahedral interstitial site. Notably, hydrogen demonstrates comparable migration energy barriers (0.17eV) when moving along both the tetrahedral and octahedral interstitial sites in close proximity to each other. By employing Arrhenius diffusion equation, we establish a fitted relationship between temperature and diffusion coefficient, providing theoretical support for investigation coating corrosion properties at elevated temperatures.