Kinetics of hydride front in Zircaloy-2 and H release from a fractional hydrided surface

The authors study the hydriding process on commercial nuclear fuel claddings from their inner surface using an ultrahigh vacuum method. The method allows determining the incubation and failure times of the fuel claddings, as well as the dissipated energy and the partial pressure of the desorbed H-2 from the outer surface of fuel claddings during the hydriding process. The correlation between the hydriding dissipated energy and the amount of zirconium hydride (formed at different stages of the hydriding process) leads to a near t(1/2) potential law corresponding to the time scaling of the reaction for the majority of the tested samples. The calibrated relation between energy and hydride thickness allows one to calculate the enthalpy of the delta-ZrH1.5 phase. The measured H-2 desorption from the external surface is in agreement with a proposed kinetic desorption model from the hydrides precipitated at the surface.