Theoretical Studies On The Structures And Properties Of Different Uranium Silicides

China's coal-based energy structure leds to environmental problems which hinders economy development in a healthy way.Developing clean energy is the way to solve the conflict between economic development and environmental protection.Nuclear energy is one of an important option to consider.The uranium-silicon system is an important nonoxide ceramics fuel.Uranium silicides have attracted extensive attention as potential candidate for the next generation nuclear fuel.U3 Si is featured by the high actinide density and the better thermal conductivity relative to conventional oxide fuels.For proper and safety operation of those advanced nuclear fuel,there still is a lots of work required to do.The structures of uranium silicides are not researched sufficiently.The prediction for defect structure and the stability of fission products also need to theoretical study so that one can learn the impact of fission products on the performance of the fuels as the fission reaction proceeds.In this work,the structures and properties of different uranium silicide fuel matrices are investigated using DFT-GGA.The lattice parameters,electronic structure and formation energies of ?-U3 Si,?-U3 Si,?-USi2 and ?-USi2 are predicted by first principles calculations.Point defects and fission products and their influence on crystal lattices are discussed.The most favorable sites of fission products(strontium,barium,cerium and neodymium)are determined in this work as well.The main results and conclusions are as follow:(1)The calculation of lattice parameters agree with the experimental values very well.The formation energies of the compounds are calculated to determine their thermal stability,which are consistent with experimental enthalpies of formation.The results also suggest that GGA-PBE approximation may be satisfactory in reproducing bulk properties and the energies of U3 Si and USi2.(2)The stability of different types of point defects is predicted by their formation energies.The results show that silicon vacancies are more prone to be produced than uranium vacancies in ?-USi2 matrix and the reason for formation of USi2-x are analyzed,while uranium vacancies are the most stable defects of other three types of crystallographic structures.(3)According to the current data,rare earth elements cerium and neodymium are found to be more stable than alkaline earth metals strontium and barium in a given nuclear matrix.Comparing the structural changes influenced by different fission products,it is also found that the highest volume change is caused by barium interstitials.(4)By calculating incorporation energies of fission products,we demonstrate that the uranium site is the most favored for all the fissions products.It is also determined that in USi2 crystal lattice fission products tend to be stabilized in uranium substitution sites,while they are likely to form precipitates from the U3 Si matrix.