The reactor, which began operating in September ahead of the grid connection, is going online 12 years later than originally planned and at a cost of around €13 billion (US$13.56 billion) – four times the original budget.

“EDF teams have achieved the first connection of the Flamanville EPR to the national grid at 11.48am. The reactor is now generating electricity,” EDF said in a statement.

The Flamanville 3 European pressurised reactor is France’s largest at 1.6GW and one of the world’s biggest, along with China’s 1.75GW Taishan reactor, which is based on a similar design, and Finland’s Olkiluoto.

It is the first to be connected to the grid since Civaux 2 in 1999 but is being brought into service at a time of sluggish consumption, with France exporting a record amount of electricity this year.

EDF is planning to build another six new reactors to fulfil a 2022 pledge made by President Emmanuel Macron as part of the country’s energy transition plans, although questions remain around the funding and timeline of the new projects.