Stress corrosion: ASN validates EDF’s schedule for weld inspection

On April 25, 2023, the French Nuclear Safety Authority (ASN) published an information note validating the strategy for controlling and repairing all reactors with regard to the risk of stress corrosion cracking phenomenon, as amended in early March 2023.

In December 2022, EDF submitted a strategy for controlling and repairing the stress corrosion cracking phenomenon (SCC) that affects part of the nuclear fleet to the ASN. In March 2023, the discovery of a particularly large crack on the Penly 1 reactor led EDF to adjust its strategy. Until then, the design of the RIS and RRA lines of the reactors was identified as the main factor in the occurrence of SCC. In the case of Penly 1, it appeared that the double repair of certain welds at the time of construction of the reactors was an aggravating factor.

Following this development, EDF counted 320 repaired welds in the fleet. A good part of them will be replaced during future unit outages. On the other hand, the electricity company has identified 69 welds that must be checked as a priority, 90% of which will be reviewed by the end of 2023 and the rest by March 2024. ASN considers the schedule appropriate in its April 25, 2023 briefing note. “the review of ninety percent of the repaired welds identified as priorities by EDF by the end of 2023 and all of these welds by the first quarter of 2024,” ASN confirms.

Additional operating measures at Nogent-sur-Seine and Cruas

“Technical exchanges between ASN and EDF focused on reactors with welds on two auxiliary lines that are considered a priority for inspection. These are Reactor 1 at the Nogent-sur-Seine power plant and Reactor 2 at the Cruas power plant,” the ASN said. The additional operating measures by EDF will be implemented until the scheduled shutdown of the reactors in September 2023. The Nogent-1 (1,300 MW) and Cruas-2 (900 MW) reactors will be connected to the grid until then.

In the wake of this validation by the ASN, EDF has republished its production forecasts for 2023, a subject on which the markets had been extremely pessimistic. The company confirms: “To date, the estimate of nuclear generation in France for 2023 remains in the range 300-330 TWh. This is well above the particularly disruptive production of 2022 at 279 TWh but still down from 2021 at 361 TWh. ■

Gaïc Le Gros (Sfen)

Photo – Nogent-sur-Seine nuclear power plant ©EDF – Didier Marc/PWP