Comments on the stability of zirconium hydride phases in Zircaloy

As part of a project for the non-destructive assessment (NDA) of hydrogen content in Zircaloy-4 tubing, a series of Zircaloy-4 slabs were submitted to accelerated corrosion autoclaving tests in 1 M LiOH, in order to obtain thick oxide layers and high hydrogen pickup. These specimens were used as primary standards for oxide thickness eddy currents (ET) NDA and as secondary standards for hydrogen content ET-NDA. Specimen preparation and the non-destructive studies have been reported elsewhere. In the present work, the evolution of the hydride phases in these autoclaved Zircaloy-4 slabs was studied over a period of about 3 years, and the results are compared to those from other authors who worked with zirconium, Zircaloy or zirconium–niobium alloys. A revision of the literature on zirconium hydrides up to 2002 is presented.