Abstract: This invention relates to a chemical method of effectively decontaminating metallic wastes that have been contaminated by radioactive substances and which have resulted from the demolition of nuclear power plants or reactors in operation. The method is that when the increase in the amount of dissolution of metal ions from the wastes causes the potential of the aqueous sulfuric acid to increase beyond a certain level, the dissolved metal ions are reduced electrolytically to control the potential of said aqueous sulfuric acid to become lower than said certain level.

Abstract: In a process for treating radioactive liquid waste having an evaporation concentration device, including a concentration vessel, and a steam heater having steam inlet and outlet lines and operating to heat, with heating steam, radioactive liquid waste in the evaporation concentration device so as to concentrate the waste, contamination of the entire steam heater system in the event of leakage is prevented or greatly reduced by the provision of: (1) a sluice valve in the steam outlet line near the heater; (2) a discharge line with a drain valve for discharging any waste fluid between the heater and the sluice valve; and (3) means for receiving radioactive waste discharged through the discharge line. In accordance with the process of the present invention, when the pressure within the steam heater is less than that within the concentration vessel, and the operation of the evaporation concentration device is to be resumed, the sluice valve is first closed and the drain valve is opened.