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

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 (3D) 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 3D 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 3D 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.