[SY-E1] Symposium E-1

[SY-E1] The Multiscale calculations on the behaviors of some nuclear fuels and cladding materials

^○shiyu du (Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, China)

For the nuclear plants, the safety and efficiency of the reactors are the most conerned issues mainly determined by the performance of the applied materials. Hence, the structural design of new nuclear fuels and the development of new generation cladding materials have been the research focus for years. In our works, we have studied the crystalline structures of different members of uranium silicides by first principle calculations. The impact of defects on the stability and lattice structure of uranium silicide from microscopic scale is investigated and predictions on the performance in the reactor are discussed. As the promising cladding materials, SiC/SiC composite is studied in our group as well. Non-equilibrium Molecular Dynamics simulations are performed to study the mechanism for the mechanical failure of the coating-matrix and coating-fiber interfaces. It is found that the mechanical strength of interface is strongly dependent on the temperature of the system. At 700-1000K, the shear strength is significantly reduced due to the phase transition of the pyrolysis carbon coatings. Furthermore, the implanted He atoms are also determined as a major factor that influence the mechanical behavior. The exsitence of He atoms in the coating materials may cause a significant increase in shear strength and have a delaying effect on the high temperature failure. The phase field formulation has been employed to investigate the abnormal grain growth behaviors for UO₂ with pores in the final stage of sintering from mesoscale. The microstructure evolution is found dependent on the total volume fraction and individual sizes of pores. The grain growth rate is evidently suppressed when the porosity is high and it is found independent of pore size at low porosity. Moreover, the smaller pores may cause worse abnormal grain growth at low porosities and more significant stagnation effect at high porosities in the sintering of UO₂.