Evaluation of Conditions for Hydrogen-Induced Degradation of Zirconium Alloys during Fuel Operation and Storage

Components for nuclear reactors are made from zirconium alloys because they have a low thermal neutron capture cross-section, high resistance to corrosion in high temperature water and acceptable mechanical strength.  A key to the successful operation of nuclear fuel is that the target burnup is attained before one of the several degradation mechanisms limits the life of the zirconium alloy fuel cladding. As burnup targets increase this goal becomes more onerous. During service the properties of the components can degrade because of irradiation damage, oxidation and hydrogen ingress. The consequence of the latter may be embrittlement and cracking. The IAEA plans to assist interested Member States' organizations in evaluation of hydrogen-induced degradation of mechanical and fracture properties  in different zirconium alloys, including both traditional and experimental materials, so that the degradation may be predicted and prevented. While the processes of time dependent crack propagation have been investigated in recently finished CRPs on Delayed Hydride Cracking in Zr pressure tubes and fuel cladding, this project will address the initial stages of crack development that define conditions when fuel integrity can be lost. The results from such a programme will also be relevant to evaluations of fuel transportation and dry storage.