基于中子成像技术的破损燃料棒锆合金包壳氢分布表征分析

Characterization Analysis of Hydrogen Distribution in Damaged Fuel Rods Based on Neutron Imaging Technology

  • 摘要: 针对压水堆燃料棒在运行过程中吸氢导致包壳析出氢化物引发失效的问题,传统破坏性分析方法存在样品制备难度高、分析位置不全面等局限。该研究针对破损燃料棒氢含量无损测定的技术挑战,采用中子成像无损检测方法开展分析。实验结果表明,中子成像技术可实现包壳氢化物分布的可视化,观察到运行工况下氢化物在包壳中的富集现象,并成功测定破损燃料棒裂纹附近的氢含量。该研究验证了中子成像对破损燃料棒氢含量分布表征分析的可行性,为锆合金包壳材料的服役性能优化及改进设计提供了关键工况下的实验数据支撑。

     

    Abstract: During the in-reactor operation of pressurized water reactor (PWR) fuel rods, hydrogen from the coolant environment diffuses into the zirconium alloy cladding, leading to the precipitation of hydrides within the zirconium matrix. This phenomenon represents a critical issue in nuclear materials because hydride formation embrittles the cladding material, which can initiate crack propagation and ultimately result in material failure. Conventional methods for quantifying the hydride content in damaged fuel rods rely mainly on destructive analysis techniques, such as post-sectioning metallographic examination or high temperature hydrogen extraction. However, these approaches suffer from significant limitations, including the complexity of preparing irradiated samples and the inability to examine multiple locations on a single specimen. Such constraints hinder a comprehensive assessment of cladding integrity under operating conditions. To address the technical challenges in hydrogen analysis, this study employed neutron imaging as an advanced non-destructive testing method. The fundamental principle of neutron imaging is based on the difference in neutron attenuation between hydrogen and zirconium atoms. Through dedicated data-processing algorithms, the neutron attenuation data were converted into hydrogen distribution maps, with corrections applied for factors such as material thickness and the neutron energy spectrum. The results clearly demonstrate that neutron imaging can effectively visualize the distribution patterns of hydrides within the cladding, revealing pronounced hydride enrichment adjacent to cracks and other structural defects. Semi-quantitative analysis indicates that the average hydrogen concentration on the surface of the irradiated fuel rod is about 100 ppm, while localized hydrogen concentrations in hydride enriched regions near cracks reach approximately 5 000-10 000 ppm. This work validates the feasibility of neutron imaging to characterize the hydrogen content in damaged fuel rods. The findings contribute to optimizing the in-service performance of zirconium alloy cladding materials and provide a basis for future design improvements aimed at enhancing reactor safety and longevity.

     

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