Method for decontaminating radioactively contaminated surfaces of metallic materials

Method for decontaminating radioactively contaminated surfaces of metallic materials with the use of nitric acid and hydrofluoric acid, comprising subjecting for at least four hours the surfaces to be decontaminated to a vapor mixture of water vapor, hydrogen fluoride vapor and nitric acid vapor, with the ratio of hydrogen fluoride vapor concentration to nitric acid vapor concentration in the vapor phase corresponding to a ratio of 2:1 to 4:1, as measured by the number of moles HF/l to number of moles HNO.sub.3 /l in a condensate formed by condensing the vapor mixture, and wherein the concentration of hydrogen fluoride vapor in the vapor mixture corresponds to a concentration in the range between 0.1 mol/l and 1.0 mol/l, as measured in a condensate formed by condensing the vapor mixture, and the concentration of nitric acid vapor in the vapor mixture corresponds to a concentration in the range between 0.05 mol/l and 0.5 mol/l measured in a condensate formed by condensing the vapor mixture.