[EPR Flamanville Series] Flamanville 3 Cleared to Continue Power Ramp-Up

After a long shutdown for maintenance operations, Flamanville 3, the EPR reactor, was reconnected to the national grid on Sunday, April 20 at 8:30 p.m. It will now continue its gradual power ramp-up, aiming for full output by the end of the summer.

Commissioning a nuclear reactor — something that hadn’t occurred in France for over 20 years — requires several shutdowns of varying durations to test the unit and all its systems under different conditions and configurations. This multi-month, step-by-step startup process ensures the delivery of a safe and reliable reactor for long-term operation. On February 15, 2025, EDF reported that Flamanville 3 was halted “following the detection of reduced performance in the EVU/SRU system.” It was ultimately reconnected to the national grid on April 19, 2025 at 8:30 p.m. According to EDF’s schedule, full nominal power output is still expected by summer 2025.

A Series of Extended Shutdowns

On February 15, 2025 at 12:30 a.m., EDF detected a malfunction in the ultimate heat sink cooling system (EVU/SRU). This system, which is activated only in exceptional severe accident scenarios, is a seawater-fed cooling circuit designed to evacuate excess heat. In accordance with safety protocols, EDF suspended the EPR’s production. “Cleaning and backflushing of the circuits allowed flow rates to return to expected levels,” the company stated at the time.

Meanwhile, a plant team carried out an intervention on a temperature sensor in the primary circuit, leading to a first extension of the shutdown on February 22. Less than a week later, on February 28, the outage was extended again. This time, maintenance operations focused on the turbine hall, with extensive adjustments to the bearings supporting and guiding the turbo-generator’s rotors to optimize performance. Restart was initially scheduled for March 30 following this work.

The outage was eventually extended until April 10 due to “additional maintenance on equipment located in the nuclear section of the facilities.” It was further prolonged one last time to “carry out maintenance operations on equipment [in the nuclear section] required for safely continuing the reactor’s power ramp-up,” EDF explained.

The EPR was thus reconnected to the grid last Sunday, following this series of outage extensions. EDF has clarified that “in the coming weeks and months, shutdowns, restarts, and reconnections to the grid will be repeated several times. These actions are normal as part of an initial startup.” All operations have been carried out in close coordination with the Nuclear Safety and Radiation Protection Authority (ASNR).

Fuel Integrity Risk

EDF has also addressed feedback from the international operation of other EPRs — namely Taishan and Olkiluoto — particularly regarding nuclear fuel behavior. In those reactors, instances of fuel rod leakage were observed, linked to anomalies that appeared during the initial power ramp-up (first operating cycle).

So far, Flamanville 3 — which is still in its first fuel cycle — has not been affected by this issue. However, EDF is taking a preventive approach and had already factored in the potential risk during its planning, starting from first criticality on September 3, 2024. “Given the duration of the power ramp-up for Flamanville 3 and following a prudent and conservative approach, EDF will take an additional measure during the first complete outage inspection by introducing a full set of non-irradiated fuel assemblies into the core before beginning the second operating cycle,” the company stated. ■