2002 年 8 巻 2 号 p. 165-170
A new alternative method for separation of Np in the first eo-decontamination step is proposed. It comprises two steps, namely, preconditioning of Np valence state in the dissolved solution of spent fuel by NO gas bubbling in HNO3 medium to produce HNO2, which is considered as salt-free process to convert Np(VI) to Np(V) and stabilization of Np(V) with urea, finally, the demonstrative counter current cascade extraction of Np(IV) and Np(V) in a miniature mixer-settler was carried out. The batch experiments show that Np(V) produced after conditioning may be slowly oxidized again to Np(VI) during standing time. Addition of urea in the HNO3 solution might enhance the stability of Np(V). On the other hand, the solvent extraction by 30% TBP/kerosene could greatly accelerate the oxidation rate of Np(V). The chemical flow sheet study at 25°C shows that, more than 98% of Np could be routed into HLLW if urea is added in the HNO3 solution. The operating temperature has great influence on the kinetics of Np(V) oxidation. If operation temperature races to 36°C and urea is not added, about 38% of Np will go along with U and Pu into organic phase. The behavior of Np(IV) during extraction shows great accumulation in the middle stages of battery.