Flamanville 3 reaches rated output for the first time

France’s Nuclear Safety and Radiation Protection Authority (Autorité de Sûreté Nucléaire et de Radioprotection, ASNR) approved an increase in the output of Flamanville 3 above 80% of its rated capacity. On Sunday, 14.12.2025, at 11:37, the unit reached 100% output for the first time.

Flamanville 3 is an EPR pressurised water reactor with an electrical output of 1650 MWe. ASNR approved the start of the unit’s commissioning in May 2024. Fuel loading followed, along with the reactor’s startup, which began in September 2024.

The unit was connected to the grid in December 2024. Since then, its output has been raised gradually in several steps. At each prescribed power level, the relevant tests and inspections are carried out, and only then can the output be increased further.

First startup of a reactor unit

Commissioning a nuclear reactor takes several months. The main systems are gradually brought to operating parameters (heating and pressurising the medium), power tests are carried out, and the unit is then connected to the grid.

After the turbine generator is connected to the grid, output continues to increase in several stages. In January 2025, the French regulator approved raising output above 25%, and further tests were carried out over the following months before moving to higher power levels.

Startup tests and regulatory oversight

ASNR said that physical tests of the reactor core at different power levels continued at this stage, supplemented by further tests, including verification of manual reactor shutdown and a test of the transition to island mode. During this test, the unit is disconnected from the grid while continuing to generate power for the plant’s own use.

The regulator carried out several inspections, analysed significant events reported by EDF and reviewed the corrective measures put in place. According to ASNR, no reason was identified to prevent a further increase in output above 80%. Oversight will continue through the subsequent stages until the commissioning tests are complete.

Project timeline and key construction milestones

Construction of the third unit at the Flamanville nuclear power plant in Normandy began in December 2007. EDF has operated two nuclear units at the site since 1986 and 1987.

Key construction milestones included placing the reactor building dome in July 2013 and installing the reactor pressure vessel in January 2014. Commercial operation was originally expected to begin in 2013, but the project faced a series of delays.

EPR reactors around the world

The first EPR units entered service at China’s Taishan nuclear power plant. Taishan 1 entered commercial operation in 2018 and Taishan 2 in September 2019. In Europe, Finland’s Olkiluoto 3 entered commercial operation in 2023. Construction of two EPR units is currently under way at Hinkley Point C in the United Kingdom.