2. Aging of materials

Some phenomena have been well taken into account at the design stage (the embrittlement of PWR vessel steel under the effect of neutron radiation, for example, or the widespread corrosion of fuel cladding), but it is important to verify over time that material degradation is as expected.

On the other hand, other phenomena were not correctly predicted at the outset and became apparent after thousands of hours of service: for example, stress corrosion cracking of nickel alloys in contact with the PWR primary medium (steam generator tubes, bolts, etc.). When this type of degradation became apparent, it was necessary to define repair solutions or more resistant replacement materials. In order to plan the replacement of defective parts and to be able to continue operating the reactors without affecting their safety, it was necessary to know the extent and severity of...