PURPOSE: To make it easy to process decontamination liquid waste and reduce the generation of secondary radioactive waste by degasing the carbon dioxide out of the decontamination liquid after electrolyzing decontaminated metals and precipitating solved iron ion as hydroxide.

CONSTITUTION: After filling a decontamination tank 1 with decontamination liquid 2, electric current is sent between a decontaminated metal 6 and an opposite electrodes. In this process the corroded film produced on the metal 6 is separated and exfoliated into flakes due to the vibration given to the decontamination liquid 2 by an ultrasonic vibrator 5 and thus radioactives are removed from the metal 6 surface. Out of the decontamination liquid 2 after the electrolyzing carbon dioxide is degassed in a degasing tank. When the RH becomes neutral, the iron ion solved from the metal 6 is presipitated as hydroxide. In a radioactive recovery section, radioactives in the decontamination liquid 2 degassed of carbon dioxide and the like are recovered as solid and the decontamination liquid 2 is withdrawn to pure water. This liquid is made into decontamination liquid with electric charge carrier of carbon oxide ion in a carbon dioxide injection tank and sent to the decontamination tank 1 for reuse. And radioactives are recovered as solid, and so the amount of secondary radioactive waste is drastically reduced.