In the face of the continuous rise in global energy demand and increasingly severe environmental challenges, nuclear fusion energy is regarded as a bright new star in the future energy field for its cleanliness, efficiency and sustainability. The high temperature environment during the operation of fusion reactors places extremely high demands on materials, and tungsten-based materials have become an ideal choice for plasma-facing components (PFC), especially the first wall and divertor, due to their excellent melting point, excellent thermal properties, low hydrogen solubility and sputtering yield.
In fusion reactors, such as tokamaks, plasma-facing materials must withstand the strong bombardment of high-energy neutrons, hydrogen isotopes (H, D, T) and helium (He) ions released by D-T fusion reactions, which can cause serious damage to the surface and interior of the materials. In particular, helium atoms are prone to combine with vacancies in the material to form helium bubbles, which in turn aggravates the retention of vacancies, causes surface roughening, and has a negative impact on the mechanical properties of the material (such as hardening and embrittlement). In addition, the density of helium bubbles formed by helium injection is much higher than that of ordinary voids, which accelerates the degradation process of the material. Therefore, it is crucial to deeply explore the formation and evolution mechanism of radiation-induced defects in plasma-facing materials.
In order to better understand the microstructural changes of tungsten materials under irradiation conditions, the research team developed a cluster dynamics model. This model comprehensively considers the generation and interaction of point defects, small defect clusters, and helium clusters, as well as the nucleation and growth process of large-size immovable defects (such as interstitial dislocation loops, voids, and helium bubbles). By introducing the atomic-scale dislocation loop puncture mechanism, the model can accurately simulate the evolution dynamics of radiation-induced defects with or without helium injection.
Research results show: 1) Under low temperature conditions (below 300K), voids and bubbles cannot form; while in high temperature environments (above 1000K) and when the dose exceeds 3dpa, the gap ring tends to disappear, which is consistent with the experimental observations . 2) As the temperature increases, the density of the gap ring increases and the size decreases, while the voids/bubbles show the opposite trend. Helium implantation promotes the nucleation and growth of vacancy-type clusters because helium atoms prefer to combine with vacancies. 3) Considering the ring punching effect can slightly accelerate bubble growth and have a significant impact on the internal pressure of the bubble and the helium vacancy ratio. 4) In order to match the pressure and helium vacancy ratio between simulations and experimental measurements, the internal pressure feedback mechanism of the loop stamping needs to be considered to effectively regulate the growth dynamics of the bubbles.
The research results have been published in "Nuclear Materials and Energy" under the title "A reduced cluster dynamics modeling of radiation damage in tungsten".
Zigong MT Cemented Carbide Tech Co., Ltd.
