Behavior of Iodine-131 in dissolution of irradiated Uranium dioxide

A hundred milligram of UO2 was irradiated in JRR-4 (burn up 0.017%) and dissolved in boiling 3 M-HNO3 (20 ml) to study the behavior of fission-product iodine (131I, ∼1 ng). During the dissolution, 80∼90% of the iodine volatilized together with 133Xe. Zeolite 13X (∼4 g) trapped completely the iodine in the dissolver off-gas. Blowing a NO2 flow through the solution was effective for expulsion of the remaining iodine and finally 90∼95% of the initial iodine was removed from the solution with the aid of addition of KIO3. The iodine species in the solution includes I2, I-, IO3- (IO4-), organic iodides and other unknown species. The expulsion operations caused the unknown species to increase in relative abundance. This tendency was also noticed for iodine of higher concentration in 3 M-HNO3. (author)