Phase analysis of hydrogen contained Zr-2.5wt%Nb CANDU pressure tube using plasmon energy loss analysis

Abstract

Canada Deuterium Uranium (CANDU) reactors use Zr-2.5Nb alloys as the pressure tube material. Ensuring optimal performance of Zr-2.5Nb pressure tubes is vital to the safety of CANDU-type heavy water reactors. Long-term use of the pressure tube induces hydrogen pickup and hydride precipitation, causing delayed hydride cracking. Therefore, to evaluate the mechanical integrity of the pressure tube, it is critical to determine the phase distributions inside the pressure tube during hydrogen charging. This study focuses on visually expressing the hydride phasesusingscanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS).By using EELS, two phase characterization possibilities were noted at the phase boundary between α-Zr and δ-hydride: nucleated β-Zr and γ-hydride and a mechanical mixture of α-Zr and δ-hydride. The first characterization possibility was reported previously by Barrowet al., and the second possibility is described comprehensively in this paper.