[en] Steam reforming method has been developed for the treatment of organic wastes which are not suitable materials (tributyl phosphate, halogenated oil) for the incineration due to large quantities of secondary wastes generation. This method consists of the gasification process in which organics are vaporized and decomposed with superheated steam and the oxidation process in which vaporized organics are decomposed by oxidizing reaction with heated air. In the gasification process, nonvolatile radionuclides are separated from vaporized waste. Therefore it can be expected that treatment of liquid waste generated from an off-gas treatment system and maintenance operation of the off-gas treatment system become easy to perform. Experimental study in which waste TBP/n-dodecane (waste TBP) containing uranium was used was conducted with the demonstration scale steam reforming system to examine the distribution ratio of uranium in the system and the feasibility of treatment of the waste TBP from September 2006 to January 2008. The effect of treatment with steam reforming system on the volume reduction of the waste TBP was compared with that of pyrolysis method. The results of these studies are as follows: The uranium contents in liquid wastes from off-gas treatment system and of exhaust gases are under the detection limits. Most of uranium compounds contained in waste TBP are separated from organics in the gasification process. Only the solid waste remained in the gasification process is the radioactive secondary waste from the treatment of the waste TBP with steam reforming system. It is considered that the maintenance operation of the equipments installed downstream of the gasification process become easy to perform because uranium compounds are hardly distributed to these equipments. More than 99% of the wastes were evaporated in the gasification process. Therefore the volume of secondary solid wastes is very small. It was estimated that the total volume of waste packages, the residual substance solidified with cement in 200 liter drum, is 30 times less as compared with that generated by treatment with pyrolysis method. These results show that the steam reforming system can achieve high volume reduction of waste TBP. (author)