Theoretical Investigation Of The Regulating Of Oxygen Concentration And The Corrosion

Nuclear reactor will produce long-lived and high radioactive nuclear waste. Disposal of the nuclear waste is a great challenge. As the development of the accelerator and the nuclear reactor technology, a new kind of strategy, named Accelerator Driven System (ADS), is designed to deal with the nuclear waste. In ADS, an accelerator is used to produce high-energy and high-current proton and the proton will bombard a target material, such as the liquid lead or the liquid lead bismuth eutectic, in which the neutron will be produced. The lead-bismuth Eutectic (LBE) is one of the most promising core coolants and the target materials in accelerator driven system, as it possesses many good properties, such as low melting point, high boiling point, and chemical stability when it is exposed to the gas and water. One of the critical issues associated with the applications of LBE is the serious dissolution corrosion of the cladding materials (steel) which is exposed to LBE. So the compatibility of the cladding materials and LBE has drawn much attention. A common method to protect the steel from corrosion is dissolving a proper concentration of oxygen in LBE, so as to form a protective oxide film at the steel surface. The protective film could segregate the steel and LBE, then the dissolution corrosion can be strikingly lowered. However, the protective film is sensitive to the concentration of O in LBE. If the concentration of O is too low, the protective oxide cannot be formed. On the contrary, the structure material may be over oxidized and the corrosion may be enhanced. Therefore, the concentration of O in liquid alloy should be properly measured and controlled. However, up to date, these problems have not been solved yet. The interaction between oxide film and the liquid alloy is important to the anti-corrosion properties of oxide film, especially for the long time run of the cladding materials. So, in this dissertation, we investigate the controlling process of O concentration in LBE from atomic side. Moreover, the influences of LBE on the anti-corrosion properties of oxide film are also studied. In addition, by using cluster dynamic method, the evolution of defects in W under the condition of ion irradiation is investigated.This dissertation contains six chapters. In the first chapter, we will describe the local structure of LBE and the technology in controlling oxygen at the beginning. Then the corrosion behavior of LBE and the structure of oxide film formed on the steel surface are illustrated. At last, we will review several multi-scale simulation methods in material science.In the second chapter, we will introduce the pair distribution function for short range order in the structure. Then we will describe the theory of cluster dynamic and our development of this method. Finally, we will give a brief description of the packages used in our calculations.In the third chapter, we start to report our research work. The local structure and the diffusion of O in LBE are investigated at first. Then we study the short range order of H and the temperature effects in LBE. At last, the reactions between H and O, as well as the equilibrium concentrations in LBE are predicted, which gives an important reference for controlling the concentration of O in experiments.In the fourth chapter, the interactions between liquid alloy and oxide film are studied. Our results indicate that lead prefers to adsorb on the surface than bismuth does, and the deposited Pb or Bi atoms facilitates the dissolving of the iron cations from the surface. Besides, our results show that Pb and Bi atoms benefits the formation of the point defects in the oxide film. At last, the effects of the doped Cr in the oxide are studied and we find that Cr will improve the anti-corrosion properties of the oxide film.In the fifth chapter, we explore the evolution of defects in W materials under the condition of ion irradiation. The results show that when the thickness of grain boundary is less than3run, the grain boundary will inhibit the diffusion of Deuterium (D) deep into the bulk material. On the contrary, when it is larger than3nm, it will act as a trap center for D aggregation. In addition, the temperature gradient effect is also studied. Our results illustrate that D will drift from high temperature regions to low temperature regions and the concentration of D at low temperature regions will be much higher than that in high temperature regions.In the sixth chapter, we summarize all results reported in this dissertation, and give an outlook for the following work.