高温气冷堆燃料颗粒的包覆层厚度高精度测量及其空间分布状态表征方法研究

With the purpose of comprehensively investigating the quality state of coated particles adopted in High Temperature Gas Cooled Reactor(HTGR) spherical fuel elements, from the microscopic and macroscopic views, an integrated imaging method combining X-ray absorption-contrast with phase-contrast image is proposed in this project. In our research, the comprehensive dialectical relations among size of X-ray focus and detector unit, image SNR (Signal to Noise Ratio) and the modulation process of phase contrast imaging are investigated. Also, the modulated model of in-line phase contrast imaging process based on the physical attributes of fuel particles and an optimizing method for imaging parameters are developed. Finally, a new proposal including the discrimination of PSF (Point Spread Function) of the spherical projection, the phase information recovery for coating layer's interface and a correction method for measurement error is suggested to improve the measurement accuracy of the thickness of coating layer of fuel particles. In the inspection of macroscopic quality state of spherical fuel elements, using 3-Dimensional CT (Computed Tomography) and absorption contrast DR (Digital Radiography), the parameters of 3-D spatial distribution of fuel particles are shown through image and graphics processing methods. The key techniques such as metal artifact correction in CT image of fuel particles, segmentation of 3-D connected images and optimizing control of blind zone of the leaky particles in no-fuel-particle region are studied in detail. In the research project, a new technique for quality assurance of spherical fuel elements will be developed, which has an important significance to improve the performance of the spherical fuel element and ensure the safety of HTGR. Meanwhile, it will lay the foundation of further developing an engineering-oriented system for quality monitoring of the spherical fuel elements adopted in HTGR.

基于X射线吸收衬度与相位衬度综合成像方法，从微观和宏观角度出发，全面解析高温气冷堆球形燃料元件的质量状态。探讨射线源焦点尺寸、探测器探元尺寸、图像信噪比以及相位成像调制过程的综合辩证关系，建立基于包覆燃料颗粒固有物理属性的同轴相衬成像过程调制模型和成像参数优化方法。开展以提高燃料颗粒包覆层厚度测量精度为目标的球投影点扩展函数的辨析、包覆层界面相位信息恢复以及测量误差修正方法研究。在球形燃料元件宏观质量状态检测方面，以三维CT和吸收衬度DR成像为手段，通过图像、图形处理方法提取燃料颗粒的三维空间分布状态参数。重点攻克燃料元件CT图像的金属伪影校正、三维粘连图像分割，以及石墨基体无燃料区外逸燃料颗粒检测盲区的优化控制。该项目研究将为球形燃料元件质量保障提供新的技术手段，对提高球形燃料元件的性能，保证高温气冷堆的安全性具有重要的意义，同时也为面向工程的燃料元件质量监测系统的开发奠定基础。

本项目基于X射线吸收衬度与相位衬度综合成像方法，从微观和宏观角度出发，全面解析高温气冷堆球形燃料元件的质量状态。探讨射线源焦点尺寸、探测器探元尺寸、图像信噪比以及相位成像调制过程理论的综合辩证关系，建立基于包覆燃料颗粒固有物理属性的同轴相衬成像过程调制模型和成像参数优化方法；提出了P-M与NL-means混合降噪算法，在有效抑制图像噪声的同时，图像边缘信息得以保留；提出了基于Canny边缘检测及矩匹配轮廓二次追踪方案，实现了燃料颗粒包覆层厚度的高精度测量；分析了外逸燃料颗粒检测盲区的形成机理，提出了成像几何参数优化方法以消除检测盲区造成的外逸燃料颗粒的漏判；针对制造工艺和传动不稳定性造成的无燃料区投影位置和投影大小的随机跳变，提出了无燃料区投影的动态标定方法；利用形态学闭运算、差运算以及图像分割技术，实现了逃逸燃料颗粒的自动识别；采用FCM（Fuzzy-C means）模糊聚类分割和区域增长三维分割技术，实现了颗粒个数、颗粒空间分布偏心度以及均匀度的量化表征。