Study On Kinetics Of Pu Reduction By Acetaldoxime And The Application Of Acetaldoxime To The Separation Of Pu From U

Usually the Purex process can be improved by simplifying the working process, optimizing equipment, and utilizing salt-free organic reducing agents etc. Therefore, the research and development of simple, economical, and effective salt-free organic reducing agents will be beneficial to the improvement of the Purex process. Among the numerous organic salt-free organic reducing agents, acetaldoxime (AO) is considered more promising due to its unique advantages. In order to apply it to the Purex process in a better way, on the basis of searching literatures about separation of Pu from U, the studies on kinetics of the reaction between acetaldoxime and nitrous acid or Pu(IV) are carried out, and then, the batch stripping experiments and the counter current cascade ones are conducted. The main contents of this paper are summarized as follows:1) The current status and trend of development of the nuclear fuel reprocessing and the Purex process are briefly introduced. Then, the methods for the separation of Pu from U in the Purex process are emphatically reviewed.2) The structure of acetaldoxime is characterized by the spectrum of IR, MS, NMR, respectively. The improved method for determining the concentration of acetaldoxime in HNO3 solution is also set up.3) The kinetic of the reaction between acetaldoxime and nitrous acid is studied by spectrophotometry. The corresponding rate equation can be expressed as-d[HNO2]/dt = k[CH3CHNOH][HNO2][H+]05The rate constant (k) equals 921.6 7.4(mol/L)-1.5min-1 at 20C, and the activation energy is found to be 27.26 5.22 kJ/mol.4) The kinetic of the reaction between acetaldoxime and Pu(IV) is studied by spectrophotometry, and the rate equation is determined as follows:-d[Pu(IV)]/dt = k[AO] [Pu(IV)]2 [HNO3]-2.1 [Pu(III)]-1The rate constant (k) equals 27.95 0.45(mol/L)1.1min-1 at 22C, and the activation energy is found to be 88.96 9.43kJ/mol.5) On the basis of batch stripping experiments and the process parameters in 1B contactor in the Purex process, a flowsheet for applying AO to separation of Pu from U is set up (6 stages for supplemental extraction, 8 stages for stripping, ratio of flow 1BS:1BF:1BX = 1:4:1 , and 0.15mol/L AO-0.5mol/L HNO3 as stripping solution). According to the above conditions, multi-stage counter current cascade experiments are performed by using 10ml-glass test tube with plug. The experimental results show that the recovery of U is 99.9996%, that of Pu is 99.99%, the separation factor of Pu from U (SFPu/u) is equal to 1.05 x 104, and that of U from Pu(SFU/Pu) is 2.7 105.In conclusion, Pu(IV) can be reduced to Pu(III) quickly by AO without any stabilizer, and acetaldoxime can be used as the scavenger for HNO2 instead of using N2H4, since it reacts with nitrous acid quickly. So, it is potential that AO could be used for separation of Pu from U in the Purex process.