The reduction of Np(VI) and Np(V) by tit dihydroxyurea and its application to the U/Np separation in the PUREX process

The reduction of Np(VI) and Np(V) by Dihydroxyurea (DHU) was studied by spectrophotometry. The results show that the reduction of Np(VI) to Np(V) by DHU is particularly fast. The apparent rate constant is 1.86 s-1 at 4 °C as [HNO3]=0.44 M and [DHU]=7.5×10-2 M. While further reduction of Np(V) to Np(IV) is so slow that no Np(IV) is observed in 2 h. The reduction back-extraction behavior of Np(VI) in 30% tri-butyl phosphate/kerosene was firstly investigated under conditions of different temperature, different concentrations of DHU and HNO3 and various phase contact time, respectively. The results show that 98% of Np(VI) in the organic phase can be stripped rapidly to the aqueous phase by DHU under the given experimental conditions. As the concentration of HNO3 in the aqueous phase increases, the stripping efficiency decreases. While the stripping efficiency increases with the increase of the concentration of DHU. Simulating the 1B contactor of the PUREX process using DHU as the stripping agent, the SFU/Np equals to 183 under the given experimental conditions. It indicates that Np will follow with Pu in the U/Pu separation stage in the reprocessing of spent fuels.