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The thermal stability of N, N-dimethylhydroxylamine (DMHAN) in the HNO3 solution was studied using microcalorimeter. The influence of concentration of HNO3, DMHAN, methylhydrazine (MH), atmosphere (air and nitrogen), and metals was investigated. The kinetic parameters and self-accelerating decomposition temperature (SADT) of the feed in process (stripping reagents 1BX, scouring agent 2DS, stripping reagents 2BX, and waste aqueous phase 2DW) were calculated by Advanced Kinetics and Technology Solutions (akts) thermokinetics software. The molar enthalpy of the reaction of NaNO2 with DMHAN and MH was also determined. The results show that the initial reaction temperature (T0) of DMHAN/HNO3 (HNO3: 1.5–3.0 mol/L, DMHAN: 0.05–0.8 mol/L) is increased as the acidity is reduced or the concentration of DMHAN is increased. Holding reductant MH made the induction period of the autocatalytic reaction longer. The air, nitrogen atmosphere, Fe, and the fission products (Zr, Ru) do not affect the decomposition of DMHAN, but the stainless steel made the T0 of DMHAN/HNO3 become lower. The SADT of 1BX/2DS, 2BX, and 2DW is 56 °C, 52 °C and 47 °C, respectively. The molar enthalpies of formation of the reaction of NaNO2 with DMHAN and MH are −411.3 kJ/mol, −246.0 kJ/mol, respectively.

This study is aimed to investigate the microstructure of UO2 pellet cut by fiber laser and subsequent nitric acid solubility. A high power laser cutting system was employed to cut fuel rod which consists of stainless steel cladding and UO2 pellets. The influences of assist gas and cutting speed on the micromorphology, element distribution and phase of the cut-off surface of UO2 pellet were discussed. And the nitric acid solubility of laser cut samples was also studied. The results showed that there are defects such as shrinkage micro-pore, fragment, cave and crack on the cut-off surface of UO2 pellet, and UO2 may be converted into U3O8. However, subsequent nitric acid dissolution experiments demonstrated that the laser cut-off samples were soluble in nitric acid, and solubility and the dissolution rate were almost the same as those of the pristine UO2 pellets. This study illustrate that the laser can be employed to cut the fuel rod with the composite structure composed of stainless steel cladding and UO2 pellets with appropriate process parameters, and it has no adverse effect on subsequent nitric acid dissolution process.

In this study, a simulated ammonium diuranate filtrate (ADUF) which was obtained by adding uranyl nitrate to a 35 g/L ammonium nitrate solution to adjust the uranium concentration to about 50 mg/L was treated by a nanofiltration process. Experiments were carried out on a plate membrane testing device with a trans-membrane pressure (TMP) range of 0.5 ∼ 3.0 MPa, a crossflow velocity range of 10 ∼ 50 cm/s and a temperature range of 5 ∼ 35 °C. The results show that NF270 membrane has good rejection property for uranium and excellent permeability for ammonium nitrate. The ammonium nitrate concentration in the permeate is about 32 g/L which means the reject ratio of ammonium nitrate is only about 10%. Though NF270 membrane shows good uranium rejection property, the corresponding permeate flux is very high. When the trans-membrane pressure is 1.5 MPa, the uranium reject ratio is 96.8% and the the corresponding permeate flux is about 80 L/(m2·h). It indicates a bright application prospect of nanofiltration process in the treatment of ADUF.

An advanced plutonium and uranium recovery process has been established based on two organic reductants, N,N-dimethylhydroxylamine (DMHAN) and methylhydrazine (MH), as U/Pu separation reagents. This Advanced Purex process based on Organic Reductants (APOR) is composed of three cycles, including U/Pu co-decontamination/separation cycle, uranium purification cycle and plutonium purification cycle. Using DMHAN and MH as plutonium stripping reagents in the U/Pu co-decontamination/separation cycle and plutonium purification cycle, the APOR process exhibits high performance with following highlights: 1) the process is much simpler because of the elimination of Tc scrubbing operation and the supplement extraction operation, 2) high efficiency of U/Pu separation can be achieved in the first cycle, 3) plutonium product solution of high concentration can be obtained in the Pu purification cycle with a simple extraction operation instead of circumfluent extraction or evaporation of the plutonium solution.

Oxidation of Pu(III) in 1 bp solution to Pu(IV) was studied using the salt-free oxidant N2O4. It was proved that the reductants N,N-dimethylhydroxylamine (DMHAN) and monomethyl-hydrazine (MMH) present in 1 bp solution of CIAE-APOR process can be oxidized and removed from the solutions also by N2O4 before the oxidation of Pu(III). The effects of the acidity, the temperature and the amount of N2O4 added on the oxidation of DMHAN and MMH were studied.

The kinetics of the reduction of plutonium(IV) by hydroxyurea (HU), a novel salt free reductant, in nitric acid solutions has been studied. The observed reaction rate can be expressed as: -d[Pu(IV)]/dt=k0[Pu(IV)]2[HU]/[H+]0.9, where k0 = 5853±363 (l1.1.mol-1.1.s-1) at t = 13 °C. The activation energy is about 81.2 kJ/mol. The study also shows that uranium(VI) has no appreciable influence on the reaction rate. Compared with other organic reductants our experiments indicate that HU is a very fast reductant for plutonium(IV).

This paper reports the effect of HNO 3 on radiation stability and radiolysis product of N,N-Diethylhydroxylamine (DEHA), which is used as a reducer in the reprocessing of spent fuel. Results show that with the addition of HNO 3 , radiation stability of DEHA is weakened obviously, the volume fraction of H 2 , CH 4 and C 2 H 4 decreases but the concentration of CH 3 COOH increases. As to 1.0 and 2.0 M HNO 3 , the concentration of CH 3 CHO increases, but it decreases when HNO 3 is 3.0 M.