W辐照损伤初期的分子动力学研究

MOLECULAR DYNAMICS SIMULATION OF INITIAL RADIATION DAMAGE IN TUNGSTEN

运用分子动力学方法,探究bcc-W在中子辐照初期,由辐照诱发的缺陷形成和演化的微观过程的原子机制.选取初始碰撞原子（PKA）能量1.0~25.0 ke V,模拟温度范围100~900 K,研究W中位移级联产生的缺陷数量及分布,PKA方向和温度对稳定Frenkel pairs数的影响,缺陷团簇以及W的离位阈能.结果表明,若级联诱发的缺陷在峰值阶段呈近球形密集分布,稳定阶段Frenkel pairs数相对较少,若缺陷呈非球形相对分散分布,稳定阶段Frenkel pairs数相对较多;稳定Frenkel pairs数受PKA方向的影响不大,且随温度升高有下降趋势;比较而言,间隙原子团簇分数比空位团簇分数高,而空位团簇倾向于形成较大的团簇;W的平均离位阈能受温度影响较小,并具有一定的各向异性.

Tungsten is a candidate material for the first wall and divertor in a tokamak fusion reactor, in which it is required to withstand a high neutron irradiation. The defects created in cascade form the primary state of damage and their subsequent evolution gives rise to important changes in their microstructures and engineering properties. However, the evolution and aggregation of radiation- induced defects in atomic level can not be ob- served by experiments up till now. In this work, molecular dynamics （MD） method was used to explore the micro- structural processes and atomic mechanism of the formation and evolution of defects in the initial stage of radi- ation in bcc-W. The range of primary knock-on atom （PKA） energies is 1.0-25.0 keV, and simulation temperature range from 100 to 900 K. The number and distribution of defects produced by displacement cascades have been studied; the influence of PKA direction and temperature on the number of steady Frenkel pairs has also been re- searched; defect clusters and the threshold energy have been simulated. The results showed that for morphology dis- tribution of defects induced in the peak time of cascade, the more intensive the defects are, the less the steady Fren- kel pairs numbers are, on the contrary, the more decentralized the defects are, the more the steady Frenkel pairs numbers are; the number of steady Frenkel pairs is insensitive to PKA direction, but has a trend to decline with the temperature elevating; the percentage of interstitial clusters is higher than that of the vacancy clusters, while va- cancies tend to form larger clusters; the average threshold energy ofW is less affected by temperature and has certain anisotropy. The results of this work can provide data for analyzing the behavior of W material under nuclear environment.