Doping by Cr is used to improve the performance of uranium dioxide (UO₂)-based nuclear fuel. However, the mechanism of structural incorporation of Cr remains unclear. Here, in order to understand this process on the atomic scale and the redox state of Cr in UO₂-based nuclear fuel, we performed intensive ab initio atomistic simulations of the Cr doped UO₂ matrix. We unexpectedly found that Cr in UO₂ exists as Cr²⁺ species and not as the widely claimed Cr³⁺. We re-evaluated previously published x-ray absorption near edge structure spectroscopy data and confirmed the computed redox state of Cr. Thermodynamic consideration shows that the favorable structural arrangement of Cr in UO₂ is given by a pair of associated Cr²⁺ and oxygen vacancy. The realism of this doping mechanism is further demonstrated by a match to the measured maximum Cr solubility and small lattice contraction.

Cr掺杂用于改善基于二氧化铀（UO ₂）的核燃料的性能。但是，Cr的结构结合机理尚不清楚。在这里，为了从原子尺度和基于UO ₂的核燃料中Cr的氧化还原状态了解这一过程，我们对Cr掺杂的UO ₂基体进行了从头开始的强烈原子模拟。我们出乎意料地发现，UO ₂中的Cr以Cr ^2+的形式存在，而不是以广泛宣称的Cr ^{3+的形式存在}。我们重新评估了先前发表的近边缘结构光谱数据的X射线吸收率，并确认了Cr的计算氧化还原态。热力学研究表明，Cr在UO中的有利结构排列₂是由一对相关联的Cr给出²⁺和氧空位。通过与测得的最大Cr溶解度和小的晶格收缩相匹配，进一步证明了这种掺杂机理的真实性。