Storm Goretti: Flamanville secured, repairs underway at the electrical substation

Equipment at the electrical substations of the Flamanville nuclear power plant was damaged following the passage of Storm Goretti over Normandy on 8 and 9 January. EDF (Électricité de France) shut down the two units that were in operation. The reactors will remain offline until 1 February, while repairs are carried out.

For the French electricity system, 2026 has started under difficult conditions. Storm Goretti swept across several French regions during the night of 8 to 9 January, causing power outages for around 380,000 households. This weather event heavily affected Normandy and led to the shutdown of the Flamanville plant. “The disconnection of nuclear reactors typically falls under the provisions put in place to ensure the safety of installations in the event of abnormal operating conditions,” EDF told Revue Générale Nucléaire.

In addition to the complete shutdown of units 1 and 3 (unit 2 is currently undergoing scheduled maintenance), equipment at the 400 kV electrical substations was damaged and must be replaced. “These works must be carried out with the equipment de-energised. This de-energisation results in the temporary unavailability of the auxiliary transformer of Flamanville 3, requiring the production unit to be kept shut down in accordance with operating procedures,” EDF stated in a press release published on 10 January. As a result, reactors No. 1 and No. 3 will remain shut down until 1 February, while the repair work is carried out.

A power plant disconnected from the grid

Taking weather forecasts into account, EDF reduced the output of units 1 and 3 to 50% and 55% respectively on the morning of Thursday 8 January. During the night, the passage of Storm Goretti caused abnormal conditions on the electricity grid. Reactor unit No. 1 entered island mode around midnight: it disconnected from the grid and produced only the electricity required for its own consumption. Island mode ensures reactor safety in the event of a grid failure, while allowing for a rapid return to power generation once normal operating conditions are restored.

For the Flamanville 3 EPR – which reached full power in December 2025 – “the turbine tripped at 00:45” following the loss of an off-site high-voltage transmission line affecting production unit No. 2. These measures made it possible to secure the turbine. Isolated from the national grid, units 2 and 3 were therefore supplied by the plant’s internal electrical systems. Then, progressively over the course of Saturday 10 January, EDF shut down the entire plant in order to begin repair work on the 400 kV transmission lines. In parallel with EDF’s operations, the French Nuclear Safety and Radiation Protection Authority (ASNR) proactively activated its crisis centre on 9 January. As a reminder, this situation is not unprecedented. In 2023, the Flamanville plant had already had to place two of its production units into island mode during the passage of Storm Ciaran.■