| The energy crisis is becoming more and more serious and nuclear energy becomes particularly important. Nuclear fusion is still rarely used due to the limitation of technology, though it has many advantages. Thorium molten salt reactor(TMSR) is one of the first launch of the strategic leading science and technology projects in Chinese academy of sciences in the six candidates of the fourth generation(Gen-IV) fission reactor. Advanced structure material must have a high resistance to the irradiation, thermal and corrosion, etc. Due to excellent high temperature properties and corrosion resistance, Hastelloys becomes one kind of candidate structural materials for advanced nuclear reactors. The mainly ingredients in Hastelloys are Ni, Mo, Cr, Fe and so on. Structural materials under high energy irradiation can produce various defects such as vacancies, interstitial, holes and dislocation loops, which will affect the material mechanics performance seriously.In this paper, the molecular dynamics method was used to simulate the cascade collision process in nickel and nickel-molybdenum alloy. It has been found that the number of defects(including self-interstitial atoms and vacancies) increased sharply and reached the maximum at the primary 2ps; then it declined significantly and reach the stable phase. Most of vacancies and self-interstitial atoms recombined and at last only a few Frenkel Pairs were left.The results show that large clusters can be formed under the high-energy irradiation in nickel. With the increasing of the PKA energy, the probability of sub-cascade formation will increase. And the defects survival efficiencies of the cascades were mainly studied under different PKA energy at 600 K. The defects survival efficiencies were all about 20% in the five different PKA energies. 70% or more of the vacancies in the form of single atomic after quenching and the largest clusters appeared in 40 ke V with the size of eight. When the energy reaches 10 ke V, the interstitial clusters accounted for more than 50% and the biggest clusters also appeared in 40 ke V with the size of 20.In nickel-molybdenum alloy, the number of defects at stable state obviously increases as the PKA energy increases. Longer time is needed to reach the displacement spike at high PKA energy. Irradiations have a significant influence on the displacement cascade under high temperature with the same PKA energy. With the same temperature and concentration of Mo, the direction of the PKA energy have small influence to the defects formations at low PKA energy. Under the same conditions, the defects number increases as the concentration of Mo increases.The NEB method and the static MD method are also used for the calculation of the defects migration characteristics in Ni. These migration energies are well agreement with experimental value. OKMC is used to simulate the evolutions of defects in Ni under different irradiation conditions. SIA and vacancy defects started to recombine at 115 K in OKMC. When temperature grew up to about 150 K, the second recombination happened. When the temperature around 350 K, the third recombination makes the further reduce of the defects. And about 550 K, the dissociation of defect clusters will induce the fouth decline.The different stages of the evolution are as follows: the stage I is at about 115 K, the stage II is at about 350 K, and the stage III is at about 550 K. The defects generated in high temperature cascades are more stable than those in the low temperature cascades. In addition, almost all the defects are annihilated during the annealing process at low PKA energy(below 10 ke V). But there will remain a large number of defects(about 60%) after annealing process when the high PKA energies(up to 20 ke V) are introduced in the cascades.The processes of the irradiation in nickel and nickel-molybdenum alloy have been simulated in this paper. This study was prepared for the experimental study of irradiation damage in Hastelloys alloy in the future. |
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