This is starting to do a lot for EDF. There has been, in recent days, the announcement of a “significant defect” on one of the emergency pipes of the Penly 1 reactor (Seine-Maritime), commissioned in the early 1990s. There is now another defect qualified as “not insignificant”, by Julien Collet, Deputy Director General of the Nuclear Safety Authority (ASN).
Two new cracks
This time it concerns reactor 2 at Penly and reactor 3 at the Cattenom power plant (Moselle), according to an ASN note updated on Thursday March 9. At Penly 2, the crack is 57mm long, less than 10% of the circumference, with a maximum depth of 12mm. The one identified at Cattenom 3 is 165 mm long (about a quarter of the circumference) for a maximum depth of 4 mm.
They are therefore a little less significant than the crack in a Penly 1 pipe which extends over 155 mm, that is to say approximately a quarter of the circumference, with a maximum depth of 23 mm, for a pipe thickness of 27 mm. A size never seen before on the French park. It would be, according to the first analyses, a stress corrosion phenomenon, probably linked to repairs of non-compliant welds at the time of construction of the plant.
Thermal fatigue
But this time, the two cracks of Penly 1 and Cattenom 3, would be due to a phenomenon called ” thermal fatigue which appears on stainless steels when a part is subjected to significant temperature variations. This phenomenon is “well-known and long-watched under historic preventative maintenance programs”according to EDF.
The cracks were discovered during inspections carried out to detect stress corrosion. Impossible to be wrong. “ The thermal fatigue cracks are very straight, while those due to stress corrosion are rather zigzag. We had already encountered them in the past on certain reactors, such as at Dampierre and Civaux. But the problem today that they have been discovered in areas where we did not expect to find them “, explains Olivier Dubois, assistant to the director of safety expertise at the Institute for Radiation Protection and Nuclear Safety (IRSN).
Expand control areas
These announcements fall to the worst for EDF which must therefore completely review its maintenance program. The group ” is working on revising its control strategy. It will be proposed to ASN in the coming days. “, he underlines in an information note published on March 8.
The policeman of the sector had already requested a revision after the discovery of the crack of Penly 1, which will require the verification of some 200 welds in the whole park. There could be substantially as many checks to do this time. “ EDF will have to adapt its maintenance program to include checks on thermal fatigue over larger areas “says the Deputy Director General of ASN. It is obviously longer.
A tight schedule
The examinations will be carried out during unit outages for conventional maintenance or fuel reloading. ” There are a limited number of people who know how to do checks and repairs. And the volume of interventions is also limited by the fact that the workers take doses of radiation,” underlines Olivier Dubois, of the IRSN.
Since the end of 2021, EDF had already identified 16 reactors (out of 56) as being more sensitive to stress corrosion. Work is in progress on ten of them and should take place by the end of the year for the other six. Thermal fatigue checks are now added. Not to mention, the six to seven ten-year inspections scheduled for this year, as well as next year, which last several months and should not be carried out during the winter period, when the demand for electricity is high.
At EDF, managing this schedule is becoming a real headache, with shutdowns that will necessarily take longer. This also means less production and therefore potentially rising prices again, if the “ serial cracks » continue.