ABSTRACT

To systematically examine the relationship between the fuel fragmentation during a loss-of-coolant accident (LOCA) and the pellet microstructure, heating tests were conducted on micro fuel samples obtained from various radial positions of high-burnup fuel. The extent of the fuel fragmentation was evaluated via fission gas release rate and post-test microscopies. The results provide direct evidence for the contribution of the high-burnup structure (HBS) on the fine fuel fragmentation during a LOCA. The paper also demonstrates that the samples with a local burnup of lower than 72 GWd/tU did not fragment severely, which is in good agreement with the previously proposed burnup threshold. Heating tests incorporating stepwise depressurization from high pressure were also conducted to examine the evolution of fission gas release throughout the depressurization. The suppressing effect of hydrostatic pressure on fuel fragmentation is further confirmed. Additionally, the paper also provides results that suggest that most of the fine fragmentation at the HBS occurs during depressurization from 20 to 2 MPa.

摘要

为了系统地检查冷却剂损失事故 (LOCA) 期间燃料碎片与芯块微观结构之间的关系，对从高燃耗燃料的各个径向位置获得的微燃料样品进行了加热测试。通过裂变气体释放率和测试后显微镜评估燃料破碎的程度。结果为 LOCA 期间高燃耗结构 (HBS) 对精细燃料碎片的贡献提供了直接证据。该论文还表明，局部燃耗低于 72 GWd/tU 的样品没有严重碎裂，这与之前提出的燃耗阈值非常吻合。还进行了结合高压逐步降压的加热试验，以检查整个降压过程中裂变气体释放的演变。进一步证实了静水压力对燃料破碎的抑制作用。此外，该论文还提供的结果表明，HBS 处的大部分细碎碎裂发生在 20 至 2 MPa 的减压过程中。