抄録
The interaction of iodine species with 60Co-irradiated extractants of 30% TBP/70% n-dodecane was examined to infer the behavior of iodine downstream of the dissolution step in reprocessing. When a simulated spent-fuel solution (in which the main iodine species was colloidal iodine) was contacted with the extractant with irradiation dose of 2.8×102C/kg or less at 25°C, 70 to 80% of iodine was transferred to the organic phase together with 100% of uranium. About 50% of the iodine was retained therein during back-extraction of uranium by water at 60°C and transferred to aqueous phase in the solvent cleaning by alkaline solution. Only 4 to 5% of iodine was finally fixed in the organic phase. When the extractant was irradiated to 103C/kg or more, a "third phase" appeared in extraction step and the majority of iodine (about 65%) was sorbed in this phase. Over 90% of elemental iodine (I2) in a UO2(NO3)2-HNO3 solution was extracted to the organic phase regardless of irradiation dose of the extractant and half of it remained therein after solvent cleaning. Iodate (IO3-) in the same solution was extracted increasingly with increasing irradiation dose of the extractant.
