Radiation stability of WWER RPV cladding materials

A study investigating the WWER-440/213 reactor pressure vessel (RPV) cladding properties and their degradation due to neutron irradiation has been recently completed under an Hungarian National Government funded project "Evaluation of the lifetime of NPP structural materials". This has been carried out in co-operation with European partners and the key results from this project are presented in this paper. The RPV cladding, designed primarily to protect the RPV ferritic steel from primary water corrosion, also has structural integrity functions. The clad is made of a thin layer of austenitic steel with good ductility and toughness that offers additional robustness to the vessel. The degradation of the properties of the cladding material needs to be carefully assessed in order to properly consider the cladding as a relevant element in the global RPV integrity assessment. By taking into account the cladding it is possible to gain safety margins. This is an important result since it has a direct impact on the global lifetime evaluation of the RPV as well as avoiding the adoption of other very expensive and less effective mitigation methods.