Update on the Flamanville EPR: the reactor has reached 100% of nuclear thermal power 
 

14 December 2025 marks a major milestone : the Flamanville 3 reactor reached 100% nuclear thermal power at 11:37am and generated 1,669MW of gross electrical power*.  

The ramp-up to 100% nuclear thermal power follows the approval by the French nuclear safety and radiation protection authority (ASNR) on 12 December 2025, to go beyond the 80% threshold.  

Reaching the 100% mark for the first time enables testing of equipment at full power, taking of measurements and verifying that everything is functioning properly. Over the coming weeks, and as part of the start-up program, the power of the reactor will vary to continue testing at different power levels and an operation will be carried out on an internal electrical substation.  

This milestone reflects the commitment and expertise of the teams of EDF and of its industrial partners over the past months to ensure the safe start-up of the reactor.  

*The nuclear thermal power of a nuclear reactor corresponds to the heat produced in the reactor core by nuclear fission. This is the total amount of heat produced by the reactor. This heat is used to produce steam that will turn the turbine. It is expressed in thermal MW (MWth). Gross electrical power is the maximum power delivered by the turbine which drives an alternator to convert mechanical energy into electricity. A nuclear reactor consumes part of the electricity it produces for its own operating needs (pumps, ventilation systems, safety systems, etc.). Net electrical power refers to the power injected into the national electricity grid. It is equal to the gross power minus its internal consumption. The maximum electrical power of the reactor may vary according to operating conditions (cooling water temperature, environmental constraints, network settings).