Neutron Irradiation Of Tungsten Investigate By OKMC Method

High-energy neutron irradiation in fusion devices poses a huge challenge to the radiation resistance of wall materials.Tungsten is regarded as the best first-wall material for fusion devices due to its advantages of high melting point,low transmutation rate,low tritium retention rate,etc.Radiation effects of tungsten has attracted intensive attention in recent years.A large number of defects is produced under high-energy neutron irradiation.These defects then diffuse and interact with each other,leading to the change of the W microstructures of and eventually the macroscopic thermodynamic and mechanical properties of W.However,due to the lack of devices providing fusion neutrons,current researches on tungsten neutron irradiation are mainly carried out in three forms:fission neutron irradiation experiments,ion irradiation experiments and multi-scale computer simulations.However,the first two cannot simulate the influence of 14.1 Me V fusion neutrons completely.Multi-scale computer simulations can make up for this shortcoming,and can study the evolution of microstructures from atomic scale to macroscale,and also predict the thermodynamic and mechanical properties of materials after irradiation.In the multi-scale calculation and simulation of fusion materials,the Object Kinetic Monte Carlo（OKMC）method plays a critical role,bridging between the small-scale research of primary radiation damage and the large-scale research of macroscopic and microstructure evolution.One of the advantages of the OKMC method is that it retains the spatial distribution of defects.It can weaken or eliminate the inhomogeneity and spatial correlation of the primary radiation damage cascade,which provides accurate input for the macroscopic simulation methods.Moreover,OKMC itself can also simulate large-scale microstructure evolution.Therefore,this study chooses the OKMC method to investigate cascade aging of primary radiation damage in tungsten under neutron irradiation and the formation mechanism of a typical microstructure in tungsten under long-term and high-dose,i.e.,void lattice.This study also proposes a feasible method to analyze the uncertainty and sensitivity of OKMC simulations.The main conclusions of the study are as follows:（1）At 363K,a 50 ns cascade aging simulation was performed on the primary radiation damage database calculated by molecular dynamics.It is found that the recombination ratio of SIA（self-interstitial atom）and vacancies decreases as the PKA（Primary Knock-on Atom）energy increases.However,there are opposite trend for certain energies due to influence of the spatial distribution of defects.Meanwhile,the proportion of SIA that can diffuse out of the cascade area and the overall diffusion capacity of SIA also decrease with the increase of PKA energy,which suggests that the increase of PKA energy will weaken the interaction between the cascades.In addition,the defect size distribution and recombination ratio obtained from the study can be used as input for larger-scale simulation methods.（2）Through long-term high-dose OKMC simulation(the dose rate is 10^-9～10^-3 dpa/s,and simulated to 2 dpa),it is found that the formation of void lattice can be divided into three stages:voids nucleation,voids arrangement ordering,and stable development of void lattice.The effects of influencing factors are also studied.It is found that the dissociation of vacancy clusters promotes the formation of void lattice,and rotation of SIA inhibits the formation of void arrays.The higher the PKA energy,the weaker the interaction between the cascades,and the more difficult it is for the void lattice to form.When the temperature is lower than the threshold temperature for a vacancy to be mobile（about 600K）,no void lattice will be formed.Increase of dose rate also inhibits the formation of the void lattice,but at high temperatures,this inhibition effect becomes weaker.In addition,increase of grain sizes also promotes the formation of void lattice.（3）Finally,this study uses Wilks non-parametric statistics to carry out the uncertainty analysis of OKMC simulation,and obtains the double-sided 95/95 tolerance interval of the number density and average size of vacancy clusters under different input parameter distribution intervals.By using the Spearman correlation coefficient to measure the sensitivity of the simulation results to the input parameters,it is found that capture radii of defects have the greatest impact on the simulation results,followed by the barrier of SIA rotation,while the influence of migration barrier of vacancy and SIA is negligible.