Abstract
Hydrogen absorbed into zirconium alloy nuclear fuel cladding as a result of the waterside corrosion reaction can affect the properties of nuclear fuel, principally through the precipitation of brittle hydride particles. Multiple phenomena are involved in this overall process: after hydrogen pickup degradation of mechanical properties is controlled by hydrogen transport, hydride precipitation and dissolution kinetics and the formation of specific mesoscale hydride microstructures. The precipitation of hydrides especially affects cladding ductility and fracture toughness, but can also affect other phenomena, including via stress-induced hydride reorientation. These processes can affect cladding performance both during normal operation and during extended dry storage, as hydride morphology can be modified during the preparatory vacuum drying processes. We review the processes of hydrogen transport, hydride precipitation and dissolution and formation of mesoscale hydride microstructures, and highlight where more research is needed, both from an experimental and from a modeling point of view.