Physical interpretation of different experimental dependencies of the hydride reorientation stress threshold on the hydrogen content in Zircaloy-2, -4

The experimental dependences of the hydride reorientation stress threshold on the hydrogen concentration in zirconium alloys presented in various publications shows a significant divergence. This discrepancy may be due to different physical interpretations of the stress threshold: through minimal absolute amount of hydrogen (few ppm) or relative (few percent) amount of reoriented hydrides. This assumption was supported by simulations with the physically-based numerical tool. The paper proposes the concept of a "representative" stress threshold, defined by the relative amount of hydrogen in reoriented hydrides. The "representative" threshold characterizes the susceptibility of dissolved hydrogen to precipitate as radially oriented hydrides under external stresses.