Up to now, the aging phenomena highlighted by the reactor operating experience especially concern:
- embrittlement due to neutron irradiation of the reactor vessel;
- thermal embrittlement of pipe steels in the primary system;
- thermal fatigue of pipes in systems connected to the primary system ("dead channel");
- stress corrosion (SG);
- stress corrosion influenced by irradiation (internal structures of the vessel);
- erosion and corrosion of internal parts of components in safety-related systems (gates of motor-operated valves);
- corrosion of anchoring devices;
- thermal aging of electrical cables;
- thermal aging of control-command components.
The corrective actions planned after incidents due to the aging of components most often involve improvements to the monitoring and maintenance programs.
For periodic visits of plants after 30 years and taking into account the wish to prolong NPP lifetime, this document provided considerations to be assessed in regard with safety requirements to be maintained.