Estimation Tests for Effecting Factor on Decontamination Property in Crystallization Process

Kusama, Makoto*; Chikazawa, Takahiro*; Tamaki, Yoshihisa*

In crystallization unit, UNH (Uranyl Nitrate Hydrate) crystals are washed by a nitric acid solution to get high decontamination factor, but the data on UNH crystals dissolution by washing procedure is insufficient to evaluate the effectiveness of crystallization unit. So, in this study, the effect of a nitric acid concentration to UNH crystals dissolution and decontamination factor was tested. As results, it was found that UNH-crystals dissolution was suppressed as the nitric acid concentration was higher, for example UNH-crystals dissolution by 1N nitric acid washing becomes half as compared with 8N solution washing. And as for the decontamination factor of UNH crystals, it was found that these values by 1N nitric acid washing raised 2-times as compared with 8N nitric acid washing. It was suggested that the decontamination factor of UNH-crystals have the correlation to UNH-crystals dissolution, and shown that UNH crystals loss by washing is 10~20wt% in this experiment.In addition, the crystallization behavior tests used a simulated spent fuel dissolved solution which was prepared by cold FP elements was carried out in a batch-wise experimental method. As results, it was found that in the condition of the feed solution in process design study, Ba element is crystallized with UNH, but other elements were remained in mother liquid. Besides, in the condition of the feed solution contained extreme quantity of Cs than process design concentration, it was found that Cs element was crystallized with UNH. On the other hand, the decontamination factor of other elements except Ba and Cs was about 10 after crystal-liquid separation by filtration, and then increased about 100 after crystal washing. It was confirmed that UNH crystal purity was increased by crystal-liquid separation and washing procedure.