Understanding the fundamental processes of plastic deformation in uranium dioxide (main nuclear fuel) is critical to predict the structural integrity of nuclear reactors under off-normal operating conditions. While the 1/2<110>{001} edge dislocation has been extensively studied in recent years due to its role as rate-limiting character for plastic deformation in the primary slip systems, much less is known about the screw dislocation, despite its recently shown involvement in the composite slip process at high temperature. Here, molecular simulations are employed to investigate the evolution of the 1/2<110> screw dislocation core structure in UO2 with temperature. First, a comparison of the various interatomic models tested at 0 K addresses the stability of a zig-zag core structure predominantly spread in {001}. Then, molecular dynamics simulations confirm the stability of the screw dislocation core spread in {001} up to 1600 K, after which a transition towards more complex core structures involving the {110} and {111} planes is characterized, with direct implications on the shear-ability of the various crystallographic planes of the fluorite structure. Further analysis reveal that the transition of the screw dislocation core, that favors thermal fluctuation of the dislocation core in {111} slip planes at high temperature, is driven by the local disordering of the anionic sublattice within the dislocation core, preceding the well-known Bredig transition in UO2. This transition of the screw dislocation core is at the roots of the composite slip process, which was recently proposed to explain the Schmid law breakdown observed in UO2 single crystal.

中文翻译：

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温度对二氧化铀中 1/2[公式省略] 螺钉位错芯的影响


了解二氧化铀（主要核燃料）塑性变形的基本过程对于预测非正常运行条件下核反应堆的结构完整性至关重要。虽然 1/2<110>{001} 边缘位错近年来因其在初级滑移系统中作为塑性变形的限速特性而受到广泛研究，但对螺旋位错的了解却少之又少，尽管最近显示它参与了高温下的复合滑移过程。本文采用分子模拟研究 UO2 中 1/2<110> 螺丝位错核心结构随温度的演变。首先，对在 0 K 下测试的各种原子间模型的比较解决了主要在 {001} 中分布的锯齿形核心结构的稳定性。然后，分子动力学模拟证实了螺旋位错核在高达 1600 K 的 {001} 中扩散的稳定性，之后表征了向涉及 {110} 和 {111} 平面的更复杂的核结构的过渡，直接影响萤石结构的各个晶体平面的剪切能力。进一步的分析表明，螺杆位错核的转变有利于在高温下{111}滑移面上位错核的热波动，是由位错核内阴离子亚晶格的局部无序驱动的，在 UO2 中众所周知的 Bredig 转变之前。螺旋位错芯的这种转变是复合滑移过程的根源，最近有人提出来解释在 UO2 单晶中观察到的施密德定律击穿。