The effect of varying nickel concentration on the hydrogen pickup fraction and corrosion resistance in Zircaloy-4

Abstract

Zircaloy-4 samples with various levels of Ni content (0–483 wt. ppm) were exposed in autoclave for up to 2800 days. Samples were destructively and non-destructively measured to determine the weight gain from oxidation and hydrogen contents to better understand the role hydrogen has in increasing oxide growth rates and to study the effect of Ni on the mechanism of hydrogen pickup in Zr alloys. Overall, additions of Ni lead to significantly higher hydrogen pickup of the alloy. As observed previously, at higher weight gains, a small decrease in hydrogen pickup fraction is observed for all alloys tested (Zircaloy-4 with and without Ni). A small beneficial effect of Ni was observed on corrosion rate when controlling for the amount of hydrogen in the material, which potentially indicates that if hydrogen content were controlled via other means (e.g., volume or other alloy additions) Ni may improve corrosion resistance of the material. Results generally support published density functional theory (DFT) hypotheses that point to an increase in hydrogen solubility or catalysis of surface reactions as the mechanism by which Ni increases hydrogen pickup. Data or future corrosion testing of alloys with Ta, V, or Ti additions could further support or refute these theories by testing aspects of the proposed mechanisms.