Development of a fluorination decontamination technique for uranium bearing waste

In this study, fluorination decontamination was investigated from the viewpoint of treating uranium bearing waste which is in a condition that is difficult to decontaminate like sludge. Since the clearance level of uranium bearing waste has not been defined yet in Japan, a radiation level of 0.3 Bq/g which is recommended by IAEA TECDOC855 was chosen and a decontamination technique was developed to achieve this level. The principle of the fluorination decontamination technique is to fluorinate uranium to get gaseous UF6 and thus remove uranium from the uranium bearing waste. ClF3 was chosen as a fluorination decontamination gas because ClF3 can convert uranium of various chemical forms into UF6 and its fluorination reactivity is higher than other interhalogen compounds. In experiments, 1 g of uranium bearing sludge was put in a rotary kiln filled with ClF3. The experimental variables were decontamination temperature, duration of ClF3 treatment, revolution speed of the kiln, pretreatment grinding period of sludge, and weight of sludge in the kiln. The results showed the sludge could be decontaminated below the clearance level when treated at 550degC for 2 h. The residue of uranium increased proportionally to the weight of sludge. An empirical formula was derived to predict decontamination performance which includes experimental variables. (author)