A decommissioning project for a uranium conversion plant was conducted to restore it to a safe environmental condition and minimal low level radioactive wastes which were converted to stable chemical forms for a long term disposal. In the middle of 2004, a decommissioning program for a conversion plant, which was constructed in 1982, and treated about 300 tons of natural uranium until it was shut down in 1992, obtained its approval from the regulatory body. Actual dismantling and decontaminating activities have been performed since July 2004 and will be finished by December 2009. The decommissioning works were mainly divided into two parts: the inside of the building containing the process equipments; the lagoon sludge generated during the plant operation. The decommissioning of the inside of the building was carried out by dismantling the process equipment, which were firstly segmented and decontaminated by polishing and washing with steam and chemicals or melting, and then decontamination for the surfaces inside the building by excavating or grinding the concrete walls. The decontamination goals were below 0.2Bq/g for the metallic segments and below 0.4Bq/cm2 for the concrete walls. Decontamination methods were selected according to the degree of contamination and a minimization of the low level radioactive wastes was conducted throughout the decommissioning work. The lagoon sludge waste had two types, one was an various inorganic nitrate salt mixture containing a very low concentration of uranium, about 200∼300ppm, in Lagoon-II and the other was an inorganic nitrate salt mixture containing a few percent of uranium in Lagoon-I. To treat these sludge wastes a thermal decomposition facility was constructed and operated to produce stable sludge wastes containing uranium oxides which are stable in the air. The final sludge wastes after a thermal treating for the sludge waste of Lagoon-I could be reused. The final residual radioactivity for the inside of the building will be measured to confirm a complete decontamination of the uranium to back ground level and then the building will be considered for another use.

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