Flamanville EPR: Two Additional Weeks of Testing Before Power Ramp-Up

The restart of the Flamanville 3 EPR has been delayed by two weeks. The postponement is linked to the reactor’s restart phase following maintenance on the primary circuit valves. Nevertheless, EDF maintains its target of reaching full power by the end of autumn.

EDF has postponed the restart of Flamanville 3 by two weeks in order to carry out operational tests under real pressure and temperature conditions. While the EPR was initially scheduled to resume operation on October 1, it will only be reconnected to the grid on October 17, according to the latest information provided by the operator. The 2025 production range for the French nuclear fleet, set between 350 and 370 TWh, remains unchanged.

Flamanville 3 has been offline since June 19 for preventive inspections on two of the three safety relief valves of the primary circuit. Located at the top of the pressurizer, these components protect the reactor by opening in the event of overpressure. Since two of the three valves did not fully meet the sealing criteria in the closed position, EDF decided to perform lapping operations. This precision technique eliminates irregularities and restores a perfectly tight closure.

In addition, although no irregularities had been found on the third valve, the French utility carried out an inspection on this component as well to ensure compliance. This operation delayed the reactor’s restart by a month and a half, from August 13 to October 1.

Requalification Required

Currently, “the valves have been dismantled and inspected,” EDF told RGN. “The parts were checked a first time, then reassembled and tested a second time to verify the effectiveness of the maintenance operation.” Maintenance work on these components is now fully complete.

However, EDF must still “requalify” these primary circuit components to finalize the EPR restart phase. The valves will therefore be tested under real operating conditions. Furthermore, “the restart tests involve bringing the various plant systems (water, air – temperature, pressure) back into service” and apply to the entire reactor, EDF explained.

Full Power Before Winter

Once these tests are completed, the reactor will once again be connected to the national power grid. “The power ramp-up will then resume, first at 60% output, then at 80% output,” EDF noted. Beyond this stage, the utility will need to obtain authorization from the Nuclear Safety and Radiation Protection Authority (ASNR) to exceed 80% of nominal capacity.

If EDF adheres to this schedule, the EPR should reach full power no later than December 21, 2025—exactly one year to the day after its first connection to the French grid. While these setbacks have already delayed the milestone of achieving full reactor power—initially expected in September 2025—they are part of the process of safely starting up the EPR. This lengthy and complex stage notably involves commissioning certain equipment for the first time and performing more than 1,500 safety tests. ■