Co And Supercritical Co <sub> 2 </ Sub> Passivation Of Uranium Metal, Atomic And Molecular Mechanism

The molecular structure, potential energy function, spectroscopic property, thermodynamics property and dynamics property of UC, UO, CUO and UCO2were systematically studied in this paper , by using Density functional B3LYP method and Gaussian98W program in which the 14 valence electrons (6s27s26p66d15f3) relativistic effective core potential (RECP) and the contract valence basis set(6s5p2d4f) /[3s3p2d2f] of uranium atom and full electronic basis set 6-311Gof carbon and oxygen were used. Based on "the bluntly thin skin" model which established by our research group for prevention of the surface corrosion of uranium, the blunt surface of uranium in CO, CO2 and the anti- oxidation mechanism of CO, CO2 for metallic U were studied under the thermodynamics principle.To prevent the corrosion of uranium, the key point is to change the surface physical and chemical property of uranium. The reported corrosion prevention technology of uranium includes the surface alloying of uranium, iron implantation of niobium, the oxidation of cathode, PVD, CVD and surface coating. In US the super critical CO2 was used to clean the surface organic stains of nuclear components and the compatibility between C02 and nuclear materials was discussed; In the meantime, the inter-reaction mechanism between uranium and environmental atmosphere and the suitable method to prevent corrosion were studied by many researchers. In China professor Wangxiaoling, Liukezhao and our research group found that besides the clean function, the super critical CO and COa gas had anti-oxidation function for the surface of uranium, so it was very important to study the anti-oxidation mechanism of the super critical CO and C02 gas for metallic U.Based on the Group Theory and the Atomic and Molecular Reaction Static, the CUO and UCO2 system were optimized by means of B3LYP method for the first time. It is shown that the CUO ( 3 A ) molecular with angular structure ( Cs ) was more stable than that of linear structure ( 3 + ) , and the energy of UCO2 ( C2v ) molecular at 5A1 state was the lowest. Then according to the convertible and transmit principle of macrocosmic process and the energy optimization principle, the correct electronic states and rational dissociation limit of those molecular were derived for the firsttime. By using the many-body expansion method, the analytical potential energy function of CUO (3A ) which reappeared the equilibrium stable state geometry and energy relationship accurately was also derived. According to the potential energy function figure potential surface static characteristics of U(3IU) +CO(X1+) reaction were discussed, it was shown that there was no saddle point and threshold energy in those reaction channels. Additionally by discussing the molecular structure, energy and electrical property of the UOC, UCO and CUO under the contract valence basis set (5s4p3d4f) /[3s3p2d2f], it was found that the UCO molecular with angular structure (3A ) had the lowest energy and the highest dissociation energy. In the meantime the structure variety and characteristic of uranium-carbon-oxygen system were discussed for the further study of the surface blunt mechanism of metallic U.Based on the many-body expansion potential energy function of CUO (X3A") molecular, the collision trajectory ,the reaction section as well as the distribution of scattering angle of products of U+CO (0,0) reaction were studied for the first time by means of the Monte-Carlo quasi-classical trajectory approach, and according to the relationship between reaction section and energy, the no threshold energy reaction could be concluded, it also indicated that the stable complex compound CUO could be formed directly after collision of U +CO, because of the long lived complex compound CUO (X3A " ) could be formed when collision initial transition energy was lower than 215.0KJ.mor1, and the reaction section of reaction decreased with the increase of transition energy, so it could be concluded that this reaction was no threshold energy reaction, this conclusion was co...