Effect of grain refinement on the corrosion behavior of Zr alloys in fluorinated nitric acid

The influence of grain size or grain refinement on the corrosion of Zr alloy is clarified by employing a series of electrochemical analyses and characterization techniques. The corrosion resistance, as a function of exposure time, F⁻ concentration, and solution temperatures, of Zr alloys with different grain sizes is ascertained. The results confirm that refining the grain size can effectively enhance the short-time corrosion properties of Zr alloy in HNO₃ with F⁻. The fine-grained Zr alloy (∼10 µm in diameter) consistently exhibits a lower corrosion current density, ranging from 18% to 46% lower than that of the coarse-grained Zr alloy (∼44 µm). The enhanced corrosion resistance is attributed to the high-density grain boundaries, which promote oxide stability, and accelerate the creation of the protective layer. The high corrosion rate and pseudo-passivation behavior of Zr alloys in fluorinated nitric acid originate from the accelerated “dissolution-passivation” of the oxide film. However, the grain refinement does not provide enduring anti-corrosion for Zr alloys. To meet the operation of spent fuel reprocessing, additional systematic efforts are required to evaluate the long-term effect of grain refinement. (Figure presented.)