The causes of increased hydrogen uptake of zirconium based fuel claddings at high burnup

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. The work performed in this study contributes to the improved understanding of the hydrogen uptake mechanism in reactor. Parameters, which have been suggested to contribute to the changes in hydrogen uptake at high burnups, have been clearly quantified