discovery of other “significant” cracks in two reactors

EDF detected another “significant” defect due to a so-called thermal fatigue phenomenon on a weld in an emergency pipe in two reactors, according to the Nuclear Safety Authority (ASN) on Thursday, one more complication that could upset the maintenance schedule for French power plants. Checks “made it possible to detect the presence of thermal fatigue cracks”, on emergency pipes “considered as sensitive to stress corrosion” in reactor 2 of the Penly nuclear power plant in Seine-Maritime and reactor 3 of the Cattenom power plant in Moselle, according to an ASN note updated on Thursday.

Phenomenon of “stress corrosion”

At Penly 2, the crack is 57 mm long, representing less than 10% of the circumference, for a maximum depth of 12 mm. “It’s not trivial, it’s a significant depth,” said AFP Julien Collet, deputy director general of ASN. The other crack was spotted at Cattenom 3, 165 mm long (representing about a quarter of the circumference) for a maximum depth of 4 mm.

This discovery comes two days after the revelation of a crack of size never before seen in the Penly 1 reactor, on an emergency pipe used to flood the reactor with water in the event of a nuclear accident. This crack “extends over 155 mm, or about a quarter of the circumference of the pipe, and its maximum depth is 23 mm, for a pipe thickness of 27 mm”, had detailed the ASN. The so-called “stress corrosion” phenomenon has been identified since October 2021 on several sites, but generated smaller cracks and on other areas of these pipes.

Soon a revised control strategy

EDF must submit a revised control strategy to ASN in the coming days. In total, the electrician will have to check 200 welds throughout its fleet, according to ASN. What potentially cause prolonged shutdowns of reactors and raise uncertainties about nuclear production in 2023. The other crack mentioned Thursday by ASN is not however linked to this phenomenon of corrosion under stress, but to that of fatigue thermal, which appears on stainless steels when a part is subjected to temperature variations.

This phenomenon is “well known and monitored for a long time under historical preventive maintenance programs”, according to EDF. On the other hand, he was not expected in the area of ​​the piping where he was discovered, according to ASN. “This does not change the short-term checks program, but EDF will have to adapt its maintenance program to include checks on thermal fatigue over larger areas”, indicated Mr. Collet.