Effect of Heating Rate on Hydride Reorientation Behavior of Zirconium Alloy Tubes under Non-Stress Loading

Zirconium alloys are widely used in nuclear water reactors as cladding materials. The cladding materials will absorb hydrogen from high temperature water during the operation of nuclear reactor. In cladding tubes, it has been common sense that circumferential hydrides form without stress, while radial hydrides can form when the hydrides are reoriented under stress loading. In this study, we found that a high heating rate can result in hydride reorientation behavior even without stress. At elevated heating rates, the zirconium alloy clad tube developed a non-uniform strain gradient along the direction of heat conduction. Hydrogen atoms migrate preferentially to areas of elevated stress and precipitate as hydrides that are perpendicular to the direction of tensile stress, resulting in the formation of radial hydrides that appear as “sun spots” macroscopically. Additionally, the high heating rate disrupts the {0001}_α∥{111}_δ, <11–20>_α∥<110>_δ orientation relationship between the hydride and the substrate, which potentially facilitates crack propagation.