Helium-to-vacancy ratio of helium bubbles in RAFM steels irradiated in STIP: A new perspective via MD simulation

YS Hu and L Peng and JY Shi and YY Ma and Y Xie and ZY Wei and YJ Sun and YX Wan, JOURNAL OF NUCLEAR MATERIALS, 616, 156096 (2025).

DOI: 10.1016/j.jnucmat.2025.156096

The helium-to-vacancy (He/V) ratio plays a crucial role in the helium bubble-induced damage mechanisms caused by neutron irradiation in reduced activation ferritic/martensitic (RAFM) steels, which are main candidate structural materials for fusion reactors. Based on the results of hardening induced by helium bubble in RAFM steel specimens irradiated in the Swiss spallation neutron source, molecular dynamics (MD) simulations were conducted to investigate the interaction between edge dislocation and helium bubble with varying sizes and He/ V ratios. The barrier strength of helium bubbles were calculated based on the dispersed barrier hardening model. From a new perspective, the He/V ratio of helium bubbles in STIP specimens was evaluated through comparing the barrier strength obtained from experimental hardening data and MD simulations. The results showed that the barrier strength of bubbles initially increased slightly as the He/V ratio increased from 0 to 0.8, reached its peak within the He/V ratio range of 0.8 to 1.1, and then decreased rapidly to a very low level. By comparing the simulated and experimental barrier strength, the He/V ratio range of bubbles in RAFM steel specimens was estimated. The He/V ratio of He bubbles in RAFM steel specimens with middle doses is found to be within the high He/V ratio range of 1.2-1.4, whereas those with low doses and a high dose are situated within the He/V ratio range of 0.8-1.1. Furthermore, the He/V ratio of the helium bubbles in RAFM steels was analyzed in conjunction with existing results.

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