A fundamental understanding of lanthanide transport in metallic fuels is critical for high fidelity modeling of the fuel-cladding chemical interaction (FCCI) phenomenon, which can lead to the formation of brittle intermetallic compounds and premature failure of the cladding. Here we report a combined ab initio density functional theory (DFT) and kinetic Monte Carlo (KMC) study of the bulk diffusivity of Nd in α-U, fully taking into account the effect of radiation enhanced diffusion. The vacancy mechanism is considered to be the dominant mechanism for the bulk diffusion of Nd since a Nd interstitial is found to be intrinsically unstable in α-U. The surface diffusivity of a Nd adatom on α-U (001) surface has been further predicted using KMC simulations parameterized by DFT calculations. The present study suggests that Nd transport via the surface diffusion mechanism can be many orders of magnitude faster than bulk diffusion. Furthermore, the results from the present lower length scale study can be used to inform mesoscale phase-field simulations to determine the effective diffusion coefficient of Nd through α-U with a porous microstructure.

对金属燃料中镧系元素传输的基本理解对于燃料-包壳化学相互作用 (FCCI) 现象的高保真建模至关重要，FCCI 现象会导致脆性金属间化合物的形成和包壳过早失效。在这里，我们报告了从头算密度泛函理论 (DFT) 和动力学蒙特卡罗 (KMC) 结合研究 Nd 在α-U中的体扩散率，充分考虑了辐射增强扩散的影响。空位机制被认为是 Nd 体扩散的主要机制，因为发现 Nd 间隙在α-U 中本质上是不稳定的。Nd吸附原子在α-U上的表面扩散率(001) 表面已使用由 DFT 计算参数化的 KMC 模拟进一步预测。目前的研究表明，通过表面扩散机制的 Nd 传输可以比体扩散快许多数量级。此外，目前较低长度尺度研究的结果可用于为中尺度相场模拟提供信息，以确定 Nd 通过具有多孔微结构的α-U的有效扩散系数。