Stress Corrosion Cracking at Civaux: An Isolated and Controlled Event

The No. 2 reactor at the Civaux nuclear power plant (Vienne, France) is currently undergoing in-depth analysis following the detection of two indications on welds in the Reactor Coolant Drain Line. These defects, one identified as Stress Corrosion Cracking (SCC) and the other as Thermal Fatigue, have brought back memories of the industrial crisis of 2022, but EDF is reassuring stakeholders.

As part of the monitoring program introduced in 2022, EDF identified two anomalies during scheduled inspections on Civaux Unit 2: SCC on one weld and thermal fatigue on another. The inspections focused on welds in the Residual Heat Removal System (RRA), which plays a role in cooling the reactor core after shutdown.

Thermal fatigue is a well-known and managed phenomenon. However, SCC became a prominent issue in France in 2022 when several cases were discovered across the nuclear fleet. “We now understand the phenomenon, we prevent it, we detect it early, but it can still reappear,” said Régis Clément, Deputy Director of EDF’s Nuclear Generation Division, during a press briefing on June 17. In this case, the affected weld had actually been replaced three years ago as a preventive measure. The origin of this recurrence is still under investigation.

One of the two elbows has already been replaced, and the second is about to be. According to EDF, it will take a few more weeks to determine why the replaced elbow has once again shown signs of SCC. The detected crack is minor: between 1 and 2 millimeters deep in piping that is several centimeters thick.

The operational impact remains limited. The restart of Civaux Unit 2, initially scheduled for mid-July, is now expected by July 30, resulting in a delay of about two weeks. “As for the broader nuclear fleet, there is currently no projected impact on availability or electricity output for 2025 or the years to follow,” said Régis Clément.

A Comprehensive and Controlled Inspection Program

Since 2023, EDF has been implementing a thorough inspection program on the most sensitive systems, in line with the strategy approved by the French Nuclear Safety Authority (ASN). This program, conducted during planned reactor outages, complements ongoing monitoring of thermal fatigue. It is based on industrialized Non-Destructive Testing (NDT) and repair methods, ensuring timely interventions during scheduled shutdowns.

“The situation at Civaux Unit 2 confirms the relevance of the inspections carried out. The inspection tools and repair techniques developed by EDF since 2022 are now fully mastered and industrialized,” EDF stated in a press release.

Out of 350 inspections planned in 2025 across five of the 16 reactors most sensitive to the phenomenon, more than 200 have already been completed with no additional SCC cases found. In 2026, three more reactors will undergo extensive inspections. ■