Decoding : What is the actual output of the Flamanville 3 EPR?
The report by the French Energy Regulatory Commission (CRE) on nuclear costs has stirred debate: is the Flamanville 3 EPR limited to 1,585 MW instead of the 1,620 MW listed on REMIT due to reduced efficiency? In reality, this difference is only a cautious modeling assumption, with no indication of decreased performance from the unit.
The publication of the CRE’s report on the production costs of the existing nuclear fleet has raised questions about the electrical output of the Flamanville 3 EPR. The Commission mentions an installed capacity of 1,585 MW for the period 2026–2031, which is 35 MW lower than the 1,620 MW value communicated on REMIT, the European platform that provides information on power plant capacity and outages. However, this difference does not indicate either a drop in efficiency or any technical modification of the reactor; it is a methodological precaution taken by the regulator in its economic modeling.
A modeling precaution, not a performance finding
In its report, the CRE states that the actual output of the EPR is not yet known, as it “will only be determined at the end of the phased power testing period.” The 1,585 MW figure used in the model therefore remains a very conservative assumption, given that final efficiency measurements are not yet available.
The regulator also specifies that no public documentation indicates output limitation or degraded efficiency. As a result, it uses the theoretical output of 1,620 MW in its own calculations, which corresponds to the official value published on REMIT.
No sign of reduced performance
At this stage, the startup tests of the Flamanville EPR are continuing at successive power plateaus, particularly on the turbine-generator group. The difference between the output published on REMIT and the figure used by the CRE in its report does not reflect any technical issue with the reactor. It is important to remember that the actual output of a nuclear unit can fluctuate depending on the season, the temperature of the cooling source, and operating conditions, without implying any inherent loss of performance.
Finally, the turbine interventions carried out in spring 2025 proceeded normally, and no vibration phenomena were observed. Since October 17, the EPR has resumed its stepwise power ascent after a long outage in mid-summer to work on primary circuit valves. Full power is still expected by the end of autumn. ■