High level waste is nuclear energy generated during the application process ,which is the greatest and the most difficult to management the waste. Proper treatment and disposal of it has already become a worldwide pro...High level waste is nuclear energy generated during the application process ,which is the greatest and the most difficult to management the waste. Proper treatment and disposal of it has already become a worldwide problem, and has become one of the key factors of restricting nuclear energy for sustainable development. Zirconolite (CaZrTi2O7) is one of the most stable mineral on the Earth and actinide major parasitic phase, therefore, it is widely used to solidify actinides separated from high level radioactive waste. In this paper, the zirconolite solid solution was synthesized by high temperature solid-stated method using a particular composition of simulated Np/Pu radioactive incineration ash (SRIA). The phase composition has been investigated by X-ray diffraction (XRD), the calcined temperature gained according to thermogravimetry scanning calorimeter (TG-DSC) analysis. Anti-leaching performance has also been researched with MCC-1 method. Results show that CaZrTi2O7 can load 40% SRIA, the accumulated leaching fraction of Ca is only about 10-4 cm in 28 days at 90 ℃, the concentrations of Zr , Ti and other noble metal ions were all less than detectability of ICP-MS, the leaching rate , normalization leaching rate, and accumulated leaching fraction of all Zr , Ti and other noble ions were 10-8 cm/d, 10-8 g/cm2·d and 10-7 cm, the results indicate that the zirconolite solidification has excellent chemical durability.展开更多
Effective adjustment and control of the oxidation state of plutonium(Pu)and neptunium(Np)is an indispensable component of Np/Pu separation in spent nuclear fuel reprocessing.Some hydrazine derivatives including methyl...Effective adjustment and control of the oxidation state of plutonium(Pu)and neptunium(Np)is an indispensable component of Np/Pu separation in spent nuclear fuel reprocessing.Some hydrazine derivatives including methylhydrazine(CH_(3)N_(2)H_(3))effectively achieves the reduction of Np(Ⅵ)to Np(V)without reducing Pu(Ⅳ).Herein,we explored the reduction mechanisms of Pu(Ⅳ)and Np(Ⅵ)by CH_(3)N_(2)H_(3)in HNO_(3)solution using scalar-relativistic density functional theory.We elucidated the difference in the reduction mechanism between Np(Ⅵ)and Pu(Ⅳ)ions by CH_(3)N_(2)H_(3).The energy barrier for the reduction of[NpⅥO_(2)(H_(2)O)_(5)]^(2+)and[NpⅥO_(2)(NO_(3))(H_(2)O)_(3)]^(+)by CH_(3)N_(2)H_(3)is largely different due to the coordination of nitrate ion.Moreover,the energy barrier of the reduction of[NpⅥO_(2)(H_(2)O)_(5)]^(2+)is apparently lower than that of[PuⅣ(NO_(3))_(2)(H_(2)O)7]^(2+),which is in line with the experimental observations.The results of Mayer bond order and localized molecular orbitals clarify the structural evolution of the reaction pathways.Analysis of the spin density demonstrates that the first Np(Ⅵ)and Pu(Ⅳ)reduction belongs to the outer-sphere electron transfer and the second Np(Ⅵ)and Pu(Ⅳ)reduction is the hydrogen transfer.This study explains theoretically why CH_(3)N_(2)H_(3)reduces Np(Ⅵ)but not Pu(Ⅳ),and helps to design promising reductants for the Np/Pu separation in spent nuclear fuel reprocessing.展开更多
文摘High level waste is nuclear energy generated during the application process ,which is the greatest and the most difficult to management the waste. Proper treatment and disposal of it has already become a worldwide problem, and has become one of the key factors of restricting nuclear energy for sustainable development. Zirconolite (CaZrTi2O7) is one of the most stable mineral on the Earth and actinide major parasitic phase, therefore, it is widely used to solidify actinides separated from high level radioactive waste. In this paper, the zirconolite solid solution was synthesized by high temperature solid-stated method using a particular composition of simulated Np/Pu radioactive incineration ash (SRIA). The phase composition has been investigated by X-ray diffraction (XRD), the calcined temperature gained according to thermogravimetry scanning calorimeter (TG-DSC) analysis. Anti-leaching performance has also been researched with MCC-1 method. Results show that CaZrTi2O7 can load 40% SRIA, the accumulated leaching fraction of Ca is only about 10-4 cm in 28 days at 90 ℃, the concentrations of Zr , Ti and other noble metal ions were all less than detectability of ICP-MS, the leaching rate , normalization leaching rate, and accumulated leaching fraction of all Zr , Ti and other noble ions were 10-8 cm/d, 10-8 g/cm2·d and 10-7 cm, the results indicate that the zirconolite solidification has excellent chemical durability.
基金supported by the National Natural Science Foundation of China(Nos.U2067212,22376197,U1867205)the National Science Fund for Distinguished Young Scholars(No.21925603)。
文摘Effective adjustment and control of the oxidation state of plutonium(Pu)and neptunium(Np)is an indispensable component of Np/Pu separation in spent nuclear fuel reprocessing.Some hydrazine derivatives including methylhydrazine(CH_(3)N_(2)H_(3))effectively achieves the reduction of Np(Ⅵ)to Np(V)without reducing Pu(Ⅳ).Herein,we explored the reduction mechanisms of Pu(Ⅳ)and Np(Ⅵ)by CH_(3)N_(2)H_(3)in HNO_(3)solution using scalar-relativistic density functional theory.We elucidated the difference in the reduction mechanism between Np(Ⅵ)and Pu(Ⅳ)ions by CH_(3)N_(2)H_(3).The energy barrier for the reduction of[NpⅥO_(2)(H_(2)O)_(5)]^(2+)and[NpⅥO_(2)(NO_(3))(H_(2)O)_(3)]^(+)by CH_(3)N_(2)H_(3)is largely different due to the coordination of nitrate ion.Moreover,the energy barrier of the reduction of[NpⅥO_(2)(H_(2)O)_(5)]^(2+)is apparently lower than that of[PuⅣ(NO_(3))_(2)(H_(2)O)7]^(2+),which is in line with the experimental observations.The results of Mayer bond order and localized molecular orbitals clarify the structural evolution of the reaction pathways.Analysis of the spin density demonstrates that the first Np(Ⅵ)and Pu(Ⅳ)reduction belongs to the outer-sphere electron transfer and the second Np(Ⅵ)and Pu(Ⅳ)reduction is the hydrogen transfer.This study explains theoretically why CH_(3)N_(2)H_(3)reduces Np(Ⅵ)but not Pu(Ⅳ),and helps to design promising reductants for the Np/Pu separation in spent nuclear fuel reprocessing.
