基于三维中子成像的锆合金包壳氢分布量化方法研究

Study on Quantitative Method for Hydrogen Distribution in Zirconium Alloy via Neutron Tomography

锆合金吸氢会导致包壳脆化,影响核燃料元件服役安全。掌握氢含量及分布的无损检测方法有助于预测和评估锆合金包壳服役性能,保障核反应堆的运行安全。本文基于三维中子成像对锆合金包壳样品中的氢分布进行定量无损表征。制备系列预设不同氢含量的Zr-Sn-Nb合金校准样品,开展三维中子成像无损测量,建立氢含量与中子图像灰度值之间的对应关系,实现未知锆合金包壳样品中氢含量和分布的精确测定。此外,利用金相法和惰气脉冲红外吸收法测氢验证了基于三维中子成像的锆合金氢分布量化方法的可行性。结果表明,三维中子成像测定的氢含量和分布与另外两种方法的结果一致。本文结果为锆合金包壳氢分布和含量研究提供了一种三维、无损检测方法,可为优化包壳材料工艺、提高服役性能提供技术支撑。

Hydrogen ingress into zirconium cladding can cause embrittlement and affects the service safety of nuclear fuel cladding. Traditional hydrogen analysis methods like hydrogen determination instrument method and metallographic method, can only give the hydrogen content or density in a small area of the sample, however, the hydrogen distribution within the zirconium alloy cannot fully understand owing to limited scope of methods. In addition, those methods require the zirconium alloy to be cut, which prevents any opportunity for other performance analysis. A non-destructive analysis of hydrogen content and distribution is helpful to predict and evaluate zirconium alloy cladding service performance. Neutron has a higher sensitivity to hydrogen than the other elements(Zr, Sn, Fe, Nb et al.) in commercial zirconium cladding. Therefore, the hydrogen in zirconium alloys can easily be seen by neutron imaging method. Herein, the neutron tomography for three-dimensional(3 D) hydrogen distribution analysis and quantitative determination in hydrided zirconium alloys were introduced. A series of Zr-Sn-Nb alloy calibration samples with designed hydrogen concentrations up to 1 150 ppm were prepared, and studied using neutron tomography. In this way, the 3 D hydrogen distribution of the calibration samples was obtained and the quantitative relationship between the hydrogen contents and image gray values was determined. It is observed that the image gray value increases linearly with the hydrogen content. Accordingly, the hydrogen content and distribution in hydrided samples are determined accurately. In addition, the metallographic method and inert gas pulse infrared absorption method were used to verify the feasibility of quantitative method for hydrogen distribution in zirconium alloys with neutron tomography. The hydrogen content and distribution determined using neutron tomography are consistent with the results of contrast methods. Consequently, neutron tomography can be efficient for 3 D hydrogen distribution analysis and quantitative determination in hydrided zirconium alloys. This work provides a three-dimensional, nondestructive testing method for the study of hydrogen distribution and content in zirconium alloy cladding, which can provide technical support for its optimization of manufacturing process and improvement of service performance.