| The thesis focuses on the study of the reactions of hydroxyurea(HU), a novel salt free agent, with uranium, neptunium and plutonium in order to investigate the possibilities of its application in the Purex process(1B) for uranium and plutonium separation. Since HU with the formula of NH2C(0)NH-OH does not introduce metal ion into the process when applied as a reductant, so it is a salt free agent. In the thesis, many research works have been done surrounding the application of HU in IB of the Purex process. The study results indicate that the usage of HU will have many advantages. The following investigations with the main results have been completed in this thesis.1. The stability of HU in HNO3 solution was studied. The results show that HU is so stable in HNO3 solutions that no appreciable decomposition has been observed as it stands for 3 days under the room temperature(~25℃) in 0.3mol/L-3mol/L HNO3 solutions. That will make the process operation easily if HU is used in the process.2. The extraction experiments indicate that HU is a strong hydrophilic reagent that the distribution percentage is about 1% into 30%TBP/kerosene from various HNO3 solutions and it is easy to be washed down from the solvent solution. Therefore it will be no problem for the solvent recovery.3. Kinetics of Pu(IV) reduced by HU was studied spectrophotometrically. The results show that the reaction rate obeys the following expression:At [NO3- ]=3mol/L and T-13℃, k0= 5829± 343(L1.1mor-1.1s-1). The activation energy is about 81.2KJ/mol. The inhibition of acidity to the Pu(IV) reduction is less in comparison with other studied organic reductants, hence it can be expected that HUhas great advantage for the application in a relatively higher acidity process. The reaction rate is near to that reduced by (N)hydroxyethyl(N')ethyl hydroxylamine(EHEH) which is the fastest reagent recently reported. As HNO3concentration is higher than 1.5mol/L, the reduction rate of Pu(IV) by HU is even greater than that by EHEH.The solvent extraction approach was also employed to study for the kinetics of Pu(IV) and HU reaction at relatively lower concentrations. The rate equation obtained with this method is:At 15℃, k0 = 14472\ 2317(mol 0.8 L-0.8min-1).Since the reaction of Pu(IV) with HU is very fast, so that the kinetic results obtained by this method will be more accurate, and the rate equation matches with the general mechanism of Pu(IV) reduction by other substitutes of-NHOH.The reaction of HU with Pu(IV) is very fast, so maybe it can meet the requirement of the centrifugal contactor with short resident time.4. The reaction of HU with HNO2 was Studied in the thesis. The results indicate that HU can react with HNO2 rapidly following the predicted reaction as: H2NCONHOH+HNO2+H+ → NH4++ CO2+N2O+H2O Rate law for the reaction obtained spectrophotometrically is:At [NO3-]=4.0mol/L and T=10℃, k0 = 0.18 ± 0.01(L1.1mol-1.1s-1). It is unusual that the reaction rate shows zero order relative to HU at excess HU present. Studying with adding various concentrations of NaNO3 indicates that salt has no influence on the reaction rate. The activation energy is about 63kJ/mol. Unlike hydroxylamine and its derivatives, HU reaction with HNO2 does not re-generate HNO2, so it can stabilize Pu(III) well in HNO3 solutions. From this it can be guessed that holding reductant willnot needed if HU is applied in the Purex process. Excessive HNO2 can destroy HU completely in HNO3 solutions, so that Pu(III) can be re-oxided to Pu(IV) and it will not influence the purification cycle of Pu crude product.5. The experiments of HU reaction with Np(VI) to Np(V) demonstrate that HU can reduce Np(VI) rapidly in HNO3 solutions, however, reducing Np(V) to Np(IV) is so slow that the reduction can not be observed during 3h from the absorbance. Since Np(V) is inextractable with tri-n-butyl phospate(TBP), it is favored for Np being directed to the aqueous phase with Pu in U, Pu separation contactor (IB) which is the expected result in advanc...
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