the steps remaining to be taken before commissioning and electricity production

Twelve years late, EDF has launched the process of “diverging” the Flamanville EPR reactor, a crucial step before electricity production.

“It’s on for the Flamanville nuclear reactor.” On the social network X, the resigning minister Agnès Pannier-Runacher, formerly in charge of the Energy Transition, was delighted to see the outcome “This construction site “unparalleled industrial”.

The many setbacks that affected the construction of the EPR – cracks in the concrete of the slab, anomalies in the steel of the tank, welding defects on the crossings of the containment building, etc. – extended the worksite by a dozen years and caused the bill to explode, now estimated at 13.2 billion euros by EDF, four times more than the initial estimate of 3.3 billion.

The Normandy EPR begins a crucial stage on Tuesday, September 3, with a view to (soon) supplying electricity to French homes. This start-up, called “divergence”, is however not the final stage.

Start the reactor

At the beginning of July, in front of journalists invited to the site, an EDF manager described the divergence in The New Factory : it’s like “starting a car while remaining in neutral”. Inside the reactor, when a neutron hits a fissile nucleus, it releases new neutrons which, in turn, hit others. We call “divergence” the initiation of this nuclear fission chain reaction which will eventually produce large amounts of energy. Divergence allows “make the reactor heart beat for the first time”according to EDF.

“There will be a nuclear reaction in the reactor, it will produce heat. However, it does not yet produce electricity”detailed Nicolas Goldberg, energy expert at Colombus Consulting, on RMC. “We are checking whether the nuclear reaction is going well, whether the reactor can increase its power a little, up to 10% of its power.”

Connect the power station to the network

To proceed to the next stage, coupling, the reactor will need to reach about a quarter of its power. According to the deputy director of EDF’s nuclear production division, the EPR should reach this level by “the end of autumn”. On this date and after “a fairly substantial testing program”the Nuclear Safety Authority (ASN) will have to give the green light for the reactor to produce electricity and be connected to the network, in order to bring electricity to French homes.

The ASN will then ensure control “subsequent stages of reactor start-up, until the maximum reactor power is reached”the authority explains on its website. In July, the deputy director of EDF’s nuclear production division had declared that it would be necessary “several months” to reach this ceiling.

With 1.6 gigawatts, the reactor will be able to “feed 2 million people”according to Emmanuelle Galichet, teacher-researcher in nuclear physics for the National Conservatory of Arts and Crafts (CNAM), interviewed on franceinfo.

Redo work

Once the reactor’s maximum power has been reached, the Flamanville EPR will operate for the duration of an operating cycle, i.e. between 15 and 18 months, before an initial shutdown, scheduled to reload the reactor with nuclear fuel (here 241 uranium assemblies).

This first interruption will give rise to new work on the EPR, which is already 12 years behind schedule. In 2014, the manufacturer Framatome had in fact identified an anomaly in the composition of the steel on certain areas of the reactor cover and it had to be replaced before the end of 2024. The ASN finally extended the use of this cover by a year and a half, in order to allow the start-up of the plant and to coincide this work with this pause, notes France 3 Normandie.

The new cover having been delivered by Framatome in October 2023, the defective model will become radioactive waste, which will be stored in La Hague, not far from Flamanville.