Stress corrosion: ASN considers that two welds on Cattenom NPP reactor 1 will need to be repaired before it can be restarted
During its treatment of the stress corrosion (SC) phenomenon affecting several of its reactors, and in accordance with the strategy it had proposed, EDF carried out inspections on the piping of the Cattenom NPP reactor 1 safety injection system. These inspections, which were carried out close to the welds liable to be the most severely affected, revealed indications  that could be attributed to SC cracking. Two of them were of significant dimensions, with maximum depths of 4.7 and 6.1 mm.
With the assistance of IRSN, ASN examined the data transmitted by EDF which aimed to justify maintaining these indications as they were and restarting the reactor for a period of eight months.
In the light of the uncertainties surrounding the defect characterisation measurements and the hypotheses and methods used in the mechanical calculations, ASN considers that the strength of the pipes affected by these two indications cannot be guaranteed. The welds concerned will therefore have to be repaired before the reactor can be restarted.
ASN considers that the other welds, on which smaller indications have been detected and for which the mechanical strength has been demonstrated, can be maintained as they are for a limited period of time. EDF has undertaken to replace all pipe sections of the safety injection system susceptible to SC cracking during the next reactor outage, scheduled for 2023.
 An indication is a signal (typically an echo for ultrasonic inspections) revealing the possible presence of a defect in the material being inspected.
Date of last update : 07/11/2022