Molecular Dynamics Simulations Of Cascades Collision In Helium-doped Vanadium

The social problems like energy crisis and environment pollution have become more serious,and the development of nuclear energy is particularly important and urgent.To date,the research and development of nuclear fusion energy and the new generation nuclear fission energy has attracted more attention around the world.In nuclear reactor,the first-wall structural material will be exposed in rigorous circumstances of the high-energy and intense-radiation neutron for a long time.Therefore,the performance of the first-wall structural materials will be one of the key decisions of nuclear reactor life.As one of the high-performance materials,vanadium-base alloys are promising candidate materials for application in nuclear reactor first-wall and blanket structures due to their excellent performance,including their low activation,high thermal conductivity,high resistance to neutron irradiation,super high temperature mechanical properties,and good compatibility with liquid lithium.In a nuclear reactor,the impurity He atoms produced by the transmutation reaction(n,?)can also be embedded into structural materials.The accumulation of He atoms may induce the formation of He bubbles,which will lead to void swelling and produce high temperature embrittlement,surface roughening,blistering,and premature creep rupture at high temperature.In order to explain the microscopic mechanism of the above phenomena in metallic vanadium,molecular dynamics simulations have been implemented to gain insight into the displacement cascades in vanadium containing substitutional He atoms with several different concentrations from 0.2 to 1.0 at%.The dependence of displacement cascades on the irradiation temperature(300 and 600 K)and energy of the primary knock-on atom(from 5 to 40 keV)have been also analyzed.It was shown that the number of Frenkel pairs increases with the increase of the energy of the primary knock-on atom.The increasing rate of the number of Frenkel pairs at 600 K is lower than that at 300 K.The predominant attention has been focused on the formation of He-vacancy clusters.The obtained results show that the number of He-vacancy clusters increases with the increase of the He concentration and the energy of the primary knock on atom.The largest size of He-vacancy is independent on the energy of the primary knock-on atom and the irradiation temperature at lowHe concentrations.The configurations of small He-vacancy clusters are different from those in iron.The He atoms in He-vacancy clusters prefer to occupy the tetrahedral interstitial sites rather than the octahedral interstitial sites.The present results provide atomic-level insights into the interactions of displacement cascades in BCC vanadium with the impurity He atoms,and also provide some essential parameters for long-scale simulations such as the kinetic Monte Carlo(KMC)method and the autonomous basin climbing(ABC)method to reproduce the experimental data.Therefore,all these theoretical simulations could be beneficial for establishing a microscopic picture of He bubbles and He embrittlement in vanadium.