When Zirconium claddings are exposed to irradiation and oxidation in reactor, after a certain period,
they may undergo a change of hydrogen uptake behavior and in some cases an increased hydrogen
pickup fraction. Hydrogen is present in reactor as a by-product of the oxidation, or through radiolysis
of the coolant. It may penetrate through the oxide and enter the underlying metal. Above a certain
concentration, it precipitates as brittle Zr-hydrides degrading the cladding’s mechanical properties.