The phenomenon is said to be thermal fatigue on a weld of an emergency pipe in two reactors. martin33 / stock.adobe.com
In reactor 2 of the Penly nuclear power station, the crack is 57 mm long. Which represents less than 10% of the circumference of a pipe.
EDF has detected another fault “not insignificant” due to a phenomenon known as thermal fatigue on a weld of an emergency pipe in two reactors, according to the Nuclear Safety Authority (ASN) on Thursday, one more complication which could upset the maintenance schedule for French power plants. Controls “allowed to detect the presence of thermal fatigue cracks”on emergency lines “considered to be sensitive to stress corrosion» in reactor 2 of the Penly nuclear power plant (Seine-Maritime) and reactor 3 of the Cattenom power plant (Moselle), according to an ASN note updated on Thursday.
At Penly 2, the crack is 57mm long, representing less than 10% of the circumference, with a maximum depth of 12mm. “It’s not trivial, it’s a significant depth”, told 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 155mm, or about a quarter of the circumference of the pipe, and its maximum depth is 23mm, for a pipe thickness of 27mm”had detailed the ASN.
A crack related to thermal fatigue
The phenomenon called “stress corrosion» has been identified since October 2021 on several sites, but generated smaller cracks and on other areas of these pipes. 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 the ASN is however not linked to this phenomenon of stress corrosion, but to that of thermal fatigue, which appears on stainless steels when a part is subjected to temperature variations. This phenomenon is “well-known and long-watched under historic preventative 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”said Julien Collet.
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