EDF announced Wednesday evening that it had decided to shut down the two Chooz reactors "as a precautionary measure", and to extend the shutdown of the two reactors at the Civaux (Vienne) power plant, after the detection of faults near welds of the safety injection circuit piping, a circuit which cools the reactor in the event of an accident.

Chooz and Civaux are reactors of the same generation - the most recent - and of the same power (1,450 MW).

"Control actions could prove necessary on the other reactors in operation", estimated in a note the IRSN, the technical arm of the Nuclear Safety Authority (ASN), the policeman of the sector.

"Once the causes of the phenomenon have been understood, it would be necessary to examine whether other reactors may be concerned," for its part, ASN told AFP.

EDF, which will produce less than expected this year, saw its listing suspended Thursday afternoon on the Paris Stock Exchange as the title fell dramatically, by 16%.

The electrician has 56 reactors spread over 18 sites in France.

For the moment, the 52 other than those of Chooz and Civaux are not affected by stops for checks or replacement of equipment.

"IRSN considers that EDF's decision to shut down the two Chooz B reactors, in addition to the two Civaux reactors, is satisfactory from a safety point of view," the institute also judges.

"The checks on the Chooz B reactors will make it possible to determine whether they are affected by the same faults. In-depth investigations must be carried out in order to determine the phenomena at the origin of stress corrosion cracks and to define the scope of the checks to be carried out. achieve ", indicates IRSN.

- Winter under vigilance -

The Nuclear Safety Authority (ASN) for its part judged, in a separate note, that EDF's decision to shut down the Chooz reactors soon was "appropriate to the situation".

It "closely follows the investigations carried out by EDF and the conclusions which will be drawn from them, in particular with regard to the in-service monitoring of this equipment", she continues.

The Civaux nuclear power station in April 2016 GUILLAUME SOUVANT AFP / Archives

ASN "authorizes work on the equipment concerned and will decide on its return to service", she concludes.

EDF explained on Wednesday that it had decided to "replace the parts concerned" in Civaux.

The shutdown of the two Chooz reactors, scheduled for Thursday and Saturday, should make it possible to check whether they are affected by the same fault.

Even before the revelation of these problems, the operator of the electricity network RTE predicted a winter under "particular vigilance" in terms of supply security for France, in particular in January and February in the event of a significant cold snap.

The country depends on nearly 70% of the atom to produce its electricity, and the health crisis has affected the maintenance schedule of power plants.

RTE assessed on Thursday the possible impact of EDF's announcements on its forecasts.

EDF for its part said Thursday that it had "re-optimized the nuclear shutdown schedule, to improve availability this winter": for example, the Flamanville 1 and 2 shutdowns were postponed by four weeks to increase by 2 GW the availability of the park in February.

The Flamanville EPR in August 2019 Lou BENOIST AFP / Archives

"We can also count on good availability of the hydraulic fleet", adds the electrician.

The Ministry of Ecological Transition assured Thursday "to constantly ensure that all measures are taken to ensure security of supply".

Minister Barbara Pompili is due to receive EDF CEO Jean-Bernard Levy on Friday morning, "for a meeting devoted to the availability of nuclear power and the security of supply this winter".

According to the Minister of Industry, at the end of November, 30% of the French nuclear fleet was at a standstill.

Agnès Pannier-Runacher had suggested to "raise our level of requirement for the availability of the park", believing that "we can collectively do better".

© 2021 AFP