An unexpected stress corrosion phenomenon on the nuclear fleet which recalls the need for safety margins In 2022, the number and duration of reactor outages were unprecedented. This situation was partly foreseeable given the operations involved in the “major overhaul” of the nuclear fleet decided on by EDF and the consequences of the postponement of certain maintenance operations as a result of the health crisis. It was made worse by the detection, during periodic inspections, of a phenomenon of stress corrosion on the welds of the safety injection system, something never before encountered on the international Pressurised Water Reactors fleet. Faced with this unexpected phenomenon EDF, which has prime responsibility for safety, decided to shut down, or extend the outage of about fifteen reactors from all plant series, in order to perform additional inspections and initiate a major investigation plan. This identified the main factors in the onset of stress corrosion and determined which reactors were most sensitive to this phenomenon, that is the four N4 type reactors and the twelve P’4 type reactors. On this basis, EDF proposed a prioritised inspection strategy to be gradually deployed on all operating reactors in the fleet. ASN considered this strategy to be appropriate and underlined that it could be revised in the light of any new knowledge. EDF decided to opt for the systematic replacement of the lines considered to be more sensitive to the phenomenon on the sixteen reactors likely to be the most severely affected, by the end of 2023. This choice is positive with regard to safety, but it does however come at a time of workload pressure in the industrial segments concerned. From left to right: Géraldine PINA JOMIR, Commissioner Jean‑Luc LACHAUME, Commissioner Sylvie CADET‑MERCIER, Commissioner Bernard DOROSZCZUK, Chairman Laure TOURJANSKY, Commissioner ABSTRACTS – ASN Report on the state of nuclear safety and radiation protection in France in 2022 3 Editorial by the Commission
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