| The nuclear energy is safety economical and clean energy. With the development of nuclear energy, more attantion has been given to the reprocessing of spent nuclear fuel. Because of increasing burnup of power reactor, more advanced technologies should be applied in the reprocessing of spent nuclear fuel. Presently the Purex process is widely used in the commercial reprocessing of spent nuclear fuel. The tendency of advanced Purex process is to improve economy and ecological environment.In Purex process, quadrivalent plutonium ion is rapidly reduced to trivalent plutonium ion by reductants in the separation of plutonium from uranium . Reductants, therefore, play an important role in the process. As a new type of organic reductants, if to be used in the spent nuclear fuel reprocessing, hydroxylamine derivatives, due to quickly reaction with Np(VI) and Pu(IV) ions and their salt-free nature, can be utilized to improve the separation of plutonium from uranium . and to decrease the quantity of salt in radioactive waste.N,N-ethyl(hydroxyethyl)hydroxylamine(EHEH) is one of the hydroxylamine derivatives. Experimental results show that kinetic rate to reduce Np(VI) and Pu(IV) ions with EHEH is faster than that with other hydroxylamine derivatives because of introducing the hydroxyl group into the reductant molecule. The EHEH as a salt-free reductant, can be utilized in the advanced Purex process, especially in centrifugal contactors having very low residence times.In order to study the possibility of EHEH being applied in the Purex process, research work has been performed and research results are as follows:(1) EHEH was synthesized by HOCH2CH2NH2 oxidation with H2O2. The structure and composition of the product were respectively characterized by elemental analysis, FT-IR spectrum, MS spectrum and NMR spectrum. The analytical method of EHEH concentration is also set up.(2) The reaction between EHEH and nitrous acid was investigated in the media ofHCIO4 . The kinetic rate equation was described as below:The rate constant equals 3.43 (mol/L) -0.93 min-1 at 25C, =1.0 mol/L and activationenergy of the reaction equals 50.0 2.5 (KJ/mol).(3) The kinetics of plutonium(IV) reduction by EHEH was studied in aqueous nitric acid media. The kinetic rate equation was described as below:The rate constant equals (7.30 0.75) 103 (mol/L) -0.54 -s-1 at T=22.5C, =2.5mol/Land activation energy of the reaction equals 196 16 (KJ/mol). The reaction rate decrease with enhancing the concentration of NO3-.The reaction rate increases with rising temperature.(4) The reduction back-extraction behavior of Pu(IV) from 30%TBP/OK with EHEH was investigated under conditions of different temperatures, different concentrations of EHEH and HNO3, various contacting-time and phase ratios respectively. It is shown that Pu(IV) from organic phase can be rapidly reduced into aqueous phase by EHEH; the batch stripping percentage of Pu(IV) approach 99% in contacting time of 5 seconds at phase ratio(O/A) 1:1, compared with 89% in 30 seconds at phase ratio (O/A) 4:1. It is also found that the higher reductant concentration , the lower acidity and the higher temperature could speed up the stripping extraction process of Pu.(5) The application of EHEH to separate Pu from U in the 1B contactor was studied by the 14-stages counter current cascade experiment. It is shown that the recovery percentage of U reaches over 99.999% and the recovery percentage of Pu reaches over 99.99% at phase ratio 1BX:1BF:1BS = 1: 4: 1. The separation factor of Pu from U (SFPu/u) is l.l 104; The separation factor of U from Pu (SFu/pu) is 3.2xl05. The results show that EHEH as a orgnic reductant has obvious effect on the separation of Pu from U. |
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