Diffusion in undoped and Cr-doped amorphous UO2
Diffusion in undoped and Cr-doped amorphous UO2
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DOI：
10.1016/j.jnucmat.2023.154270
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发表时间：
2023-01
影响因子：
3.1
通讯作者：
M. Owen;M. Cooper;M. Rushton;A. Claisse;William E. Lee;S. Middleburgh
中科院分区：
文献类型：
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作者：
M. Owen;M. Cooper;M. Rushton;A. Claisse;William E. Lee;S. Middleburgh
UO2燃料芯块通常掺入氧化铬以获得良好的性能，如更高的密度、更好的热稳定性、更大的颗粒尺寸、更好的芯块-包层相互作用范围，以及在瞬变过程中增加裂变气体保留量。铬在二氧化铀中的溶解度极限很低，过去的实验工作报告的溶解度极限在0.004到0.06%wt.%之间。由于它的低溶解度，可能会发生铬离子向晶界的偏聚。此外，如在其他陶瓷中观察到的那样，这些边界的复杂性可能很高，导致沿边界的无序或无定形区域，从而影响燃料芯块的一系列材料和操作性能。为了评估这些无序区，在这项工作中，我们研究了非晶态的未掺杂和掺铬的UO2系统(含10-50at.%Cr3+)，这些系统已经用经典的分子动力学方法进行了模拟，将Cr3+加入到了常用的CRG势库中。计算了氧离子的扩散系数、指前因子和扩散活化能，评估了结构和外在物种对迁移的影响。未掺杂的非晶态系统中的氧扩散比晶态的要快得多。氧在掺杂体系中的扩散随着铬浓度的增加而降低，突出了添加剂对保留裂变产物和其他迁移物种的重要性。
UO2fuel pellets are often doped with chromium oxide to obtain favourable properties such as higher density, improved thermal stability, large grain sizes, improved pellet-clad interaction margins, and increased fission gas retention during transients. Chromium has a low solubility limit in UO2, with past experimental work reporting solubility limits ranging between 0.004 to 0.06 wt.% Cr. Due to its low solubility, segregation of Cr ions to the grain boundary may occur. Further, the complexity of these boundaries may be high as observed in other ceramics resulting in disordered or amorphous regions along the boundary, affecting a range of material and operational properties of the fuel pellet. To assess these disordered regions, in this work we study amorphous undoped and Cr doped UO2systems (containing 10–50 at.% Cr3+) that have been modelled using classical molecular dynamics methods incorporating Cr3+into the well-used CRG potential library. Diffusion coefficients, pre-exponential factors, and activation energies for diffusion were computed for oxygen ions, assessing the impact of structure and extrinsic species on migration. Oxygen diffusion was observed to be much faster in the undoped amorphous system compared to its crystalline counterpart. Oxygen diffusion in doped systems decreased with increasing Cr concentration, highlighting the importance of additives to retain fission products and other migratory species.