Abstract Phase field models are developed to study the gas bubble migration in uranium dioxide nuclear fuel in which a large temperature gradient exists during the operation. In this work, thermal diffusion mechanism for nanosized gas bubbles and vapor transport process for micron-sized gas bubbles are considered, respectively. In both cases, gas bubbles migrate to the high-temperature area. Due to the velocity difference between leading and trailing edges of the gas bubbles, nanosized gas bubbles are elongated along the temperature gradient direction when thermal diffusion is dominated. Micron-sized gas bubbles are either compressed along temperature gradient direction to form lenticular shape bubbles or elongated along temperature gradient direction, depending on the location of the gas bubbles within the fuel pellet. Initial gas bubble radius has no significant effect on the gas bubble migration velocity for both thermal diffusion and vapor transport mechanisms. We notice that the shape change of the gas bubble due to vapor transport mechanism has no significant effect on the migration velocity. Furthermore, the center cavity formation is also captured by our model which is due to the migration and accumulation of lenticular gas bubbles at the center of the fuel pellet. The modeling results compare well with experimental observations and theoretical analysis in the literature.

中文翻译：

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温度梯度下 UO2 核燃料中气泡热迁移的相场研究

摘要 建立了相场模型来研究二氧化铀核燃料在运行过程中存在较大温度梯度的气泡迁移问题。在这项工作中，分别考虑了纳米气泡的热扩散机制和微米气泡的蒸汽传输过程。在这两种情况下，气泡都会迁移到高温区域。由于气泡前缘和后缘之间的速度差异，当热扩散占优势时，纳米气泡沿温度梯度方向被拉长。根据气泡在燃料芯块内的位置，微米级气泡要么沿温度梯度方向压缩以形成透镜状气泡，要么沿温度梯度方向拉长。对于热扩散和蒸汽传输机制，初始气泡半径对气泡迁移速度没有显着影响。我们注意到由于蒸汽传输机制引起的气泡形状变化对迁移速度没有显着影响。此外，由于透镜状气泡在燃料芯块中心的迁移和积累，我们的模型也捕获了中心空腔的形成。建模结果与文献中的实验观察和理论分析相当。由于透镜状气泡在燃料芯块中心的迁移和积累，我们的模型也捕获了中心空腔的形成。建模结果与文献中的实验观察和理论分析相当。由于透镜状气泡在燃料芯块中心的迁移和积累，我们的模型也捕获了中心空腔的形成。建模结果与文献中的实验观察和理论分析相当。