Atomistic Simulation Of Irradiation Effects In Helium-accumulated Iron And Vanadium

Nowadays,energy and environmental issues have attracted much attention,and the development of resource rich and clean energy resources has become increasingly urgent.Fusion nuclear energy has been considered as one of the effective ways to solve the energy and environmental issues because of its unique advantages.The research and development of materials with high performance is one of the key problems in the development of fusion nuclear power.Reduced Activation Ferritic/Martensitic steel(RAFM)and vanadium alloys have been considered as an important candidate of structural materials in future fusion reactors.Appled as the first wall of blanket materials,they will subject to the damage from the irradiation of high-energy particle and the accumulation of helium atoms induced by transmutation reactions.With respect to Fe,the predominant composition of RAFM,m olecular dynamics method has been utilized to investigate the effects of helium contents and their position,irradiation temperature and the ene rgy of primary knock-on atoms(PKAs)on displacement cascades.We have carefully discussed the variation of displacement processes,the number of defects,as well as the distribution and the clustering of cascade defects.With respect to vanadium,the basement of vanadium alloys,we have subsequently performed many ab initio calculations to study the primary behaviors of helium atoms.Based on the results,a new V-He interatomic potential has been developed within the theoretical framework of s-band model.The dynamics behaviors of helium atoms are studied with the present potential.Finally,the effects of helium concentration,the temperature and the energy of PKAs on the generation of defects,the displacement processes as well as the distribution and clu stering of cascade defects.The results of displacement cascades in iron and vanadium have been compared to reveal the similarities and differences.In the present work,it has been found that helium atoms prefer to occupy tetrahedral interstitial sites in vanadium and the helium clusters tend to present in symmetry configurations.Interstitial He atoms could migrate with low barrier energy of 0.06 e V from a tetrahedral to another first-nearest neighbor tetrahedral interstitial site,which is similar to the situations in iron.Interstitial He atoms tend to bind to each other with low binding energies and the trapping of He atoms depend much on the pre-existing defects and vanadium,their self-trapping seems to be of little importance.The results of displacement cascade in He-doped iron have revealed that the increase of PKA energy could promote the production in iron with either substitutional or interstitial He atoms.The production of defects can be decreased by the increase of substitutional He atoms at low temperature.In contrast,the defect number increases with the increase of substitutional He atoms at high temperature.In the case of interstitial He-doped iron,the production of defects increases with the increase of helium contents.The increasing tendency is independent on temperature,while the increasing rate can be increased by the increase of irradiation temperature.In contrast,the increase of substitutional He atoms in vanadium could increase the number of survived defects at both high and l ow temperatures,the increase of defect number with the increase of substitutional He atoms can be accelerated by the increase of either PKA energy or environment temperature.The increase of interstitial helium atoms seems to play little role in the produ ction of defects in vanadium.The increase of PKA energy linearly increases the number of defects,and the increasing rate at low temperature is higher than that at high temperature,which is contrary to the situation in vanadium doped with substitutional He atoms.Furthermore,the number of defects increases linearly with the increase of PKA energy in interstitial He-doped vanadium,but it increases nonlinearly with the increase of PKA energy in interstitial He-doped iron.The distributions of cascade defects are similar in either vanadium or iron doped by substitutional or interstitial He atoms.The defects distribute in shell-like regions within cascade region,where vacancies stay at core and self-interstitial atoms stay at peripheral regions of cascade.The number density of He atoms at core region of cascade is higher than that in rest region.With respect to the clustering behaviors of defects,it is revealed that the number of clusters increases with the increase of PKA energy in substitutional He-doped iron,which derives from the distribution of the number of vacancy clusters on cluster size.In iron with interstitial He atoms,clustering of He atoms increases with the increase of PKA energy and helium concentration.Most He atoms have clustered into Hen clusters.The number of He-vacancy clusters increases with the increase of PKA energy or with the number of interstitial He atoms.Higher PKA energy could lead to more He-vacancy clusters.Moreover,the number of vacancy clusters decreases with the in crease of He atoms.With respect to vanadium,the increase of PKA energy could increase the number of clusters in either substitutional or interstitial He-doped vanadium.The effect of irradiation temperature on cluster number is of great diversity in vana dium doped by He atoms of deferent type,substutional or interstitial type.In the presence of substitutional He atoms,the increase of temperature lead to the increase of cluster number,where the tendency is originated by the variation of the number of v acancy clusters.In interstitial He-doped vanadium,the increase of temperature results in the decrease of cluster number and the tendency may results from the variation of the number of Hen clusters.The increase of interstitial helium atoms increase the number of clusters,which is of much deference from the situation in substitutional He-doped vanadium.In vanadium doped by substitutional He atoms,the effects of helium contents on the number of clusters depend on the size of clusters,essentially depend on the type of defects clusters.