Hydrides and delayed hydrogen cracking in zirconium and its alloys

A critical review is presented of published data on hydrogen, hydrides, and delayed hydrogen cracking (or hydrogen-induced delayed cracking, HIDC) in zirconium and its alloys. It is shown that factors such as solution temperature, cooling rate, and applied or residual stresses greatly affect the hydride morphology and orientation. The most detrimental hydride morphology is shown to be that when the hydride is oriented normal to the applied stress and has the morphology of a continuous sheet. Although knowledge of the mechanism(s) of delayed hydrogen cracking has improved greatly in the past five years, further research is needed to provide a better understanding of the process. The review concludes with a discussion of delayed hydrogen cracking in the practical case of nuclear-reactor pressure tubes, and presents possible remedies to ensure no further reoccurrence of the phenomenon in commercial reactors.