Washing of Uranyl Nitrate Hexahydrate Crystals with Nitric Acid Aqueous Solution to Improve Crystal Quality

To develop a uranium crystallization process for advanced aqueous reprocessing, two method experiments were investigated to evaluate the effect of crystal washing on uranyl nitrate hexahydrate (UNH). In one experiment, crystal washing was carried but using a uranyl nitrite Solution with varying concentrations of HNO3 in washing Solutions, and in the other, it was conducted with a dissolver solution of the irradiated fast neutron reactor core fuel. In the crystal washing experiments with the uranyl nitrate Solution, the UNH crystals were immersed into a uranyl nitrate solution containing Ce, which was washed out in the mother liquor on the surface of the UNH crystals using an HNO3 solution. The experimental results showed that the decontamination factor (DF) of Ce increased with decreasing HNO3 concentration of the washing solution. However, because the UNH crystals tended to dissolve in low HNO3 concentration solutions, the yield decreased as a result of the washing operation. In the crystallization experiment using a dissolver solution derived from the irradiated fast neutron reactor core fuel, the DFs of the liquid impurities for the UNH crystals were improved with each crystal washing. However, their values approached a constant value because the inclusions within the UNH crystal were not removed by the crystal washing operation. On the other hand, solid impurities such as Cs2Pu(NO3)(6) and Ba(NO3)(2) remained in the UNH crystals after several crystal washing operations.