Cocrystallization of Uranyl and Plutonyl Nitrate Hexahydrates

Abstract

In the system UO₂(NO₃)₂–PuO₂(NO₃)₂–HNO₃–H₂O with the ratio Pu/(U + Pu) = 0.3–0.5 and stabilization of the pair U(VI)–Pu(VI), the crystallization of (U, Pu)O₂(NO₃)₂·6H₂O occurs in accordance with the metric of the phase diagram of the system UO₂(NO₃)₂–HNO₃–H₂O with coefficient of cocrystallization of plutonium 0.804 ± 0.028. This condition holds in the sector of the working lines of the crystallization process that correspond to the minimum content of uranium in the mother solution. The degree of enrichment of the mother solution is determined by the crystallization temperature, i.e., the mass fraction of the mother solution in the total mass of the system. The constancy of the coefficient of cocrystallization with the technologically important parameters of the process makes it possible to use the metric of the solubility diagram of the system UO₂(NO₃)₂–HNO₃–H₂O to calculate the crystallization of (U, Pu)O₂(NO₃)₂·6H₂O with the crystalline phase with the required composition being obtained.