乏燃料后处理用合金腐蚀行为研究进展

The expansion of nuclear power necessitates the reprocessing of accumulated spent nuclear fuel urgently. Dissolvers and evaporators are critical for reprocessing spent nuclear fuel, where near-boiling concentrated nitric acid is used to dissolve solid fuel. Severely acidic and oxidative conditions during reprocessing accelerate the corrosion of structural materials, thus threatening their service life and safety. Therefore, a review of the corrosion behavior of alloys used in spent-fuel reprocessing offers high scientific and engineering value, under the background of emphasizing the urgency to develop highly corrosion-resistant alloys to enhance reprocessing capabilities. This comprehensive analysis summarizes the corrosion behaviors, influencing factors, and principal challenges associated with three typical alloys used in spent nuclear-fuel reprocessing: low-carbon stainless steel, titanium alloys, and zirconium alloys. Results indicate that the corrosion rates of low-carbon stainless steel, titanium alloys, and zirconium alloys in a nitric-acid environment decrease sequentially by orders of magnitude, with zirconium alloys exhibiting low corrosion rates in the 10^-4 range. The complex conditions encountered by spent-fuel dissolvers and high-level waste evaporators, including variations in the nitric-acid concentration and temperature, and the introduction of oxidative ions from actinides, fission products, and corrosion products generated during spent-fuel dissolution affect the corrosion resistance of these materials. Increased temperature and nitric-acid concentration are detrimental to low-carbon stainless steel and zirconium alloys but are beneficial for enhancing the stability of the oxide film on titanium alloys. Oxidizing ions increase the corrosion rate of low-carbon stainless steel but promote the formation and repair of oxide films on titanium and zirconium alloys, thereby inhibiting their corrosion. Stainless steel maintains good corrosion resistance at nitric-acid concentrations below 8 mol / L; however, at higher concentrations and temperatures or in the presence of oxidizing ions, intergranular corrosion occurs because of the preferential dissolution of the passivation film at the grain boundaries. Titanium alloys exhibit excellent corrosion resistance in high-temperature, high-concentration nitric acid but demonstrate a high corrosion rate in weakly oxidizing nitric-acid vapor and condensate phases owing to insufficient Ti⁴⁺ for forming a protective TiO₂ oxide film. Among the three materials, zirconium alloys indicate the lowest corrosion rate in nitric acid. However, in fluorinated nitric acid, the corrosion rate of zirconium alloys increase because of the susceptibility of their passivation film to damage. Furthermore, the potential for stress corrosion cracking in zirconium alloys must be considered. The intergranular corrosion mechanism of stainless steel, the tri-phase corrosion mechanism of titanium alloys, and the corrosion mechanism of zirconium alloys in fluorinated nitric acid are elucidated. Finally, an outlook on critical areas that require further investigation for the development of these alloys is provided.