Controls of chromium and third element contents in nickel-base alloys for corrosion resistant alloys in hot HNO3–HF mixtures

Corrosion resistances of nickel-base alloys in HNO3–HF mixtures were investigated to apply them to FLUOREX process, which is advanced hybrid process of fluoride volatility and solvent extraction for next-generation spent nuclear oxide fuel reprocessing. Many types of Ni–Cr and Ni–Cr–X (X = Mo, W, Nb, Ti, Si, Cu) ingots were experimentally manufactured and the desirable chromium and third element contents in nickel-base alloys were discussed in narrow range to improve the corrosion resistance in hot HNO3–HF mixtures. From the results of corrosion tests, Ni–45Cr–0.25Mo alloy exhibited the best corrosion resistance in this study. The corrosion rate was 0.17 mm/y in 8 M HNO3–0.1 M HF solutions at 373 K and it provided good performance as corrosion resistant materials. In conclusion, the controls of higher chromium content and a small amount of molybdenum in nickel-base alloys are significant to improve the corrosion resistance in HNO3–HF mixtures condition for the FLUOREX process.