The effect of F⁻ on the passivation and repassivation of titanium in a simulated spent fuel reprocessing environment was examined using a custom-designed scratching electrode device. Electrochemical experiments and characterization of the passive film revealed that F⁻ accelerates both cathodic and anodic reactions of titanium. The critical concentration phenomenon of F⁻ on intact and scratched titanium surfaces in hot HNO₃ solutions can be attributed to competitive adsorption between F⁻ and NO₃⁻. Below the critical concentration, F⁻ primarily affects the outer layer of the passive film, while above it, F⁻ penetrates the entire passive film, significantly reducing corrosion resistance. The lower critical concentration on scratched surfaces (0.5 mmol/L) compared to intact surfaces (1 mmol/L) is due to enhanced F⁻ adsorption caused by the presence of scratches. It is indicated that regular monitoring of F⁻ concentrations and minimizing scratches on titanium surfaces to prevent corrosion failure are imperative during the spent fuel reprocessing process.