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

摘要

The reduction of Np(VI) and Np(V) by Di-hydroxyurea (DHU) was studied by spectrophotometry. Theresults show that the reduction of Np(VI) to Np(V) by DHU isparticularly fast. The apparent rate constant is 1.86 s~(-1)at 4 °Cas [HNO_3] = 0.44 M and [DHU] = 7.5 x 10~(-2) M. While fur-ther reduction of Np(V) to Np(IV) is so slow that no Np(IV)is observed in 2 h. The reduction back-extraction behavior ofNp(VI) in 30% tri-butyl phosphate/kerosene was firstly in-vestigated under conditions of different temperature, differentconcentrations of DHU and HNO_3and various phase contacttime, respectively. The results show that 98% of Np(VI) in theorganic phase can be stripped rapidly to the aqueous phase byDHU under the given experimental conditions. As the concen-tration of HNO_3in the aqueous phase increases, strippingefficiency decreases. While the stripping efficiency increaseswith the increase of the concentration of DHU. Simulatingthe 1B contactor of the PUREX process using DHU as thestripping agent, the SF_U/Np equals to 183 under the givenexperimental conditions. It indicates that Np will follow withPu in the U/Pu separation stage in the reprocessing of spentfuels.