The incident at the Civaux plant, which is offline for maintenance and tests, risks delaying its return to service at a time that France is worried about its ability to produce enough electricity over the winter.

The plant, the most modern in the French network, was shut in August 2021 after corrosion problems were detected in the welds used in its emergency cooling system.

The incident in Civaux on November 2nd “was absolutely not a weld that gave way”, Regis Clement, deputy head of EDF’s nuclear production unit, told reporters.

A pipe linked to the primary cooling system of one of the reactors ruptured, leading high-pressure steam to escape as well as a radioactive “metal object” that had to be retrieved via a robot, Clement added.

Around 80 cubic metres of waste water resulting from the leak had been captured.

“There is no risk for the environment or for public health,” the deputy head of France’s IRSN nuclear safety regulator, Karine Herviou, told franceinfo radio.

The discovery of the corroded welds at Civaux last August led EDF to shut 12 reactors built to the same design for testing.

Almost half of the country’s 56 reactors are currently offline, meaning the country is expected to have to buy electricity from the European electricity market this winter.

The Civaux plant had been scheduled to come back on stream in January. Clement said it was “too early” to say if the ruptured pipe would delay this.

Under pressure from the government to speed up its maintenance work, Clement said on Tuesday that EDF was aiming to have 42 reactors online by December 1st and 46 by January 1st, compared to just 30 currently.

Around 500 specialist welders are currently working on the cooling systems, including 100 contractors brought in from the United States and Canada.