NUMERICAL-SIMULATION OF NEPTUNIUM EXTRACTION BEHAVIOR IN CO-DECONTAMINATION STAGE FOR LATE SPLIT PUREX SYSTEM

Numerical simulation of neptunium concentration profiles is carried ou t in order to understand the extraction behavior of neptunium in the c o-decontanimation stage which decontaminates through two extraction ba nks before the uranium and plutonium partitioning steps. Simulation re sults show that leaking of neptunium to the waste stream at the second extraction bank is caused by reduction from Np(VI) to Np(V) unextract ed by TBP in the presence of nitrous acid of 10(-3) mol/l. It is found that the prevention of the reduction reaction from Np(VI) to Np(V) is effective for the recovery of neptunium with uranium and plutonium in to the product stream. Two methods for the recovery of neptunium are s uggested; i) to decrease residence time in the acid adjustment vessel located between first and second extraction banks, ii) to diminish nit rous acid in the aqueous phase by hydrazine. Simulation results show t hat the recovery of neptunium with uranium and plutonium is improved f rom 40 to 60% and from 40 to 70% by the first and the second methods, respectively.