An employee of the Chinon Integrated Expertise Laboratory (Lidec) at the Chinon nuclear power plant, January 26, 2023 in Indre-et-Loire (AFP / GUILLAUME SOUVANT)
The pipe lab: EDF’s Chinon Integrated Expertise Laboratory (Lidec) inspects the piping of nuclear power plants under all welds, placing it at the forefront of the stress corrosion crisis affecting the French fleet.
Within the Chinon power plant (Indre-et-Loire), the Lidec – unique laboratory in France – extends over several gray buildings where wind tunnels hum. Its missions: monitor reactor vessels, optimize maintenance programs and check the parts delivered by suppliers.
Philippe Fièvre, head of the materials and chemistry department of the industrial department of EDF, at the Chinon nuclear power plant, on January 26, 2023 in Indre-et-Loire (AFP / GUILLAUME SOUVANT)
Since the discovery in the Civaux power plant (Vienne) in October 2021 of a corrosion problem on the water pipes used to cool the reactor in the event of an emergency, the Lidec – which has a hundred technicians, engineers and experts– working at full speed.
“The piping was cut on Civaux and arrived here to carry out expertise. Since that date, we have been mobilized (…) on stress corrosion”, says Philippe Fièvre, head of the materials and chemistry department of the management. industrial EDF.
Cracks were then detected on pipes from other power stations, leading to reactor shutdowns. Consequence: this winter, a level of nuclear production at its lowest.
But not all plants are affected, nor even all the circuits in affected plants.
A technician operates mechanical arms in a high-activity cell at the Chinon nuclear power plant on January 26, 2023 in Indre-et-Loire (AFP / GUILLAUME SOUVANT)
“Our role is to provide our expertise to limit the phenomenon. The second step is to understand why we manage to obtain a few fine cracks on certain pipes”, details the EDF framework.
“We are really specialized in the expertise of metallic materials, mainly the steels which constitute the major part of the power stations”, he insists.
– “No tolerance threshold” –
At Lidec, pieces of steel pipes 3 cm thick and 25 in diameter arrive from all over France.
An employee of the Chinon Integrated Expertise Laboratory (Lidec) at the Chinon nuclear power plant, January 26, 2023 in Indre-et-Loire (AFP / GUILLAUME SOUVANT)
These 30 cm samples comprising a weld and weighing about fifty kilos are then cut into pieces of a few centimeters.
They are polished for a long time to obtain an absolutely smooth surface, a “mirror polish”. A necessary step to pass under the optical microscope.
On a screen, a technician displays images in black, white and shades of gray. A crack appears, gigantic. In reality, it only measures 300 microns, for about ten wide.
“From the moment there is a defect, it must be repaired. There is no tolerance threshold. The precautionary principle is EDF culture”, asserts Philippe Fièvre.
The entrance to the Lidec hot laboratory at the Chinon nuclear power plant, January 26, 2023 in Indre-et-Loire (AFP / GUILLAUME SOUVANT)
“We have to show that we are impartial,” he insists. “Everything we do is verifiable. If we hide something, we lose all credibility. There is no point, it is not safe. The proof is that we stopped our slices for microcracks.”
In another part of the Lidec, called “hot”, a technician dexterously operates mechanical arms several meters in length. They pass through a meter-long concrete wall, shielding the operator from radiation. The man, who wears a dosimeter like all the employees, reproduces the same steps as in the “cold” part. But in front of a 70 cm thick leaded glass porthole.
In one of these 17 “high activity cells” that counts the heart of the Lidec, is an electron microscope.
The “local crystallographic indexing” is checked there, that is to say the orientation of the crystals around the weld. In short, the hardness of steel.
A technician operates mechanical arms in a high-activity cell at the Chinon nuclear power plant on January 26, 2023 in Indre-et-Loire (AFP / GUILLAUME SOUVANT)
“The welding causes hardening on the pipes, which makes them more susceptible to corrosion”, explains the technical referent Frédéric Renaud. Under the pressure of the water, the stainless steel pipe is subjected to forces which can cause “progressive cracking” around the welds.
And the expert has not finished examining them… Since the end of 2021, Lidec has inspected 150 welds and its program will still be largely devoted to corrosion in 2023.
With, each time, the fear of having to shut down a reactor.
© 2023 AFP
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