Simulation Study Of The Irradiation Cascade Process In Al₃U And Pu₃Ga

The aluminum-based dispersion uranium fuel is an important nuclear fuel,which can effectively reduce uranium enrichment and greatly enhance the fuel burnup.However,since the aluminum-based dispersion fuel is produced by dispersing uranium-containing fuel particles in an aluminum substrate,this will inevitably lead to the interdiffusion of between the uranium particles and the aluminum substrate,which will form a uranium-aluminum compound at the interface.In a nuclear reactor which uses the aluminum-based dispersion fuel,this uranium-aluminum compound will also get irradiated by the neutrons as the nuclear fuel does,and that will lead to the swelling of the nuclear fuel thereby reducing the lifetime of the nuclear fuel.Due to the interdiffusion and the presence of uranium-aluminum compounds,it is necessary to study the irradiation behavior and primary radiation damage of uranium-aluminum compound(mainly Al3U)under high temperature and high flux neutron irradiation.One of the important indicators for studying the irradiation cascade process is the displacement threshold energy.Due to the special requirements of the irradiation environment,it is usually not easy to experimentally study the fuel swelling problem caused by irradiation,mainly because it takes long time to acquire the data and the risk of data contamination is high,and the cost of the experiments is very high.However,computer simulations will greatly avoid these problems and give results that match the experiments very well.Therefore,this thesis used the molecular dynamics method to simulate the irradiation cascaded collision of the Al3U system.In particular,the average displacement threshold energy of the A1 atom in the Al3U is 41 eV,while the average displacement threshold energy of the U atom is 20 eV,and there are ectopic atomic chains and weak focus in the[110]closed-pack surface.We also simulated the irradiation cascaded collision of the Al3U under high energy and the secondary separation phenomenon was observed,which will lead to the long-range diffusion of the radiation point defects.Moreover,the number of remained defects is independent of the initial outcoming direction of the PKA,while exponentially depends on the energy of the PKA,and this exponential relationship is fitted.The main configuration of the remained defects is that the large vacancy cluster in the middle is surrounded by isolated interstitial atoms,which tend to form vacancy inside the Al3U.We also studied the basic irradiance properties of the Pu3Ga system.On the one hand,it has a similar spatial structure to that of Al3U,so the related simulation method is easy to transplant.On the other hand,the study of the radiation properties of the Pu3Ga system will help understand the long-range storage of Pu/Ga compound,which is a major issue of the disposal of the nuclear weapons after the Cold War.Because there is not any good potential model for the Pu system which can well describe the irradiation property of Pu,we first modified the current potential model by the revised second nearest neighbor embedded atom method,and applying this potential in the molecular dynamics method,we measured the fundamental properties of the Pu,which fitted well with the experiments.We also investigated its displacement threshold energy of the Pu3Ga system and found that of the Pu and Ga atom is 32 eV and 43 eV,respectively.In summary,using the molecular dynamics method in this thesis,we have calculated the irradiation parameters and given the results of primary irradiation damage of two similar systems of Al3U and Pu3Ga,in which Al3U is used as the major system.Besides the corresponding displacement threshold energy,the cascaded collision results indicated that the defects inside the Al3U can easily cover the entire bulk phase and are mainly expressed in the form of vacancy clusters,which is important for the understanding of the radiation swelling of the Al3U.For the Pu3Ga,we first gave the corresponding atom displacement threshold energy surface,which laid a solid foundation for further research on the irradiation process of the Pu3Ga system.