Effect of tensile loading on irradiation creep behavior of graphite crystal: a molecular dynamics study

DB Xiong and DKL Tsang, NUCLEAR SCIENCE AND TECHNIQUES, 36, 90 (2025).

DOI: 10.1007/s41365-025-01675-7

The operational lifespan of nuclear graphite is significantly affected by irradiation creep, yet the microstructural mechanism underlying this creep phenomenon remains unclear. Some theories attempt to link microstructural evolution with creep behavior, but the rapid migration rate of defects under irradiation and loading makes it difficult to capture the specific evolution process experimentally, resulting in a lack of direct structural evidence. Therefore, in this study, molecular dynamics simulations are employed to investigate the irradiation behavior and microstructural migration under external loading. The aim is to provide microstructural evidence for theories such as the dislocation pinning-unpinning and crystal yielding. The results demonstrate that high tensile loads can increase the potential energy and reduce threshold displacement energy of graphite crystals. Consequently, displacement damage probability and creep rate increase, which is not considered in previous theories. Meanwhile, different creep mechanisms are observed at different damage states and applied loads. In low-dose damage states dominated by interstitials and vacancies, the pinning-unpinning process at basal plane may be caused by a defect diffusion mode. Under high stress levels, direct breaking of pinning structures occurs, leading to rapid migration of basal planes, demonstrating the microstructural evolution process of irradiated crystal yielding and plastic flow. In high-dose damage states characterized significantly by amorphous components, short-range atomic diffusion can become the dominant creep mechanism, and diffusion along the c-axis of graphite crystals is no longer constrained. These findings provide a crucial reference for understanding the irradiation and creep behavior of nuclear graphite in reactors.

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