Flamanville 3 EPR Expected to Reach Full Power by the End of Autumn

After being shut down for about three months for operations on the primary circuit safety valves, the Flamanville 3 reactor is now expected to reach full power no later than the end of autumn 2025. This new delay does not affect EDF’s nuclear generation forecasts.

The full power milestone of Flamanville 3 has been postponed to the end of autumn 2025 at the latest, in order to carry out maintenance operations on the three primary circuit safety valves. While this setback disrupts EDF’s initial goal of achieving full power in September, it remains part of the safe startup process of the reactor, which includes tests covering more than 1,500 criteria. The testing phase, launched on September 2, 2024—after the Nuclear Safety Authority (ASN) gave its authorization to begin reactor startup operations—allows for all adjustments and interventions to be carried out so that the EPR can complete its first production cycle with maximum safety and reliability.

This delay does not change EDF’s nuclear output range for 2025, which remains between 350 and 370 TWh. Furthermore, nuclear generation for the first half of 2025 is expected to reach 181.8 TWh, 4.4 TWh more than during the same period last year. “The startup of an EPR is a long and complex process, with some equipment being commissioned for the very first time,” EDF stressed in a press release issued on August 25.

Precision machining required on the valves

The reactor has been kept offline since June 19 for preventive inspections on two of the three main primary circuit safety valves [1]. These components, located at the top of the pressurizer, protect the primary circuit by opening in case of overpressure. When closed, they must also maintain tight sealing. “Two of the three valves operated correctly in their opening and closing function, but did not fully meet sealing requirements, which could eventually lead to equipment degradation and malfunction,” EDF explained to RGN.

The teams therefore focused their work on this point. After disassembly and diagnostics, they performed a lapping operation. “This precision technique consists of finely polishing the metallic surfaces responsible for sealing, eliminating irregularities, and restoring perfect leak-tight closure,” EDF explained on the Flamanville 3 site.

Although irregularities had only been observed on two of the three valves, “the analyses conducted, in line with our safety requirements, led us to schedule an inspection of valve No. 1, even though it showed no malfunction” [2]. EDF also noted that these operations take time due to the precision required and the cramped workspace, which makes it necessary to adapt and check the lifting equipment for each valve replacement. This third inspection explains the additional month-and-a-half shutdown, extending the restart from August 13 to October 1. The state-owned company emphasized to RGNthat this extension does not block all reactor tests, as other equipment trials can still be carried out while the unit is offline.

A significant event without impact

At the beginning of August, EDF also reported a Level 1 (anomaly) Significant Safety Event on the International Nuclear and Radiological Event Scale (INES), which occurred at the reactor [3]. During a diagnostic performed on a safety injection circuit pump, “a valve associated with this pump opened several times when it should have remained closed to ensure isolation of the circuit,” EDF noted in a press release on August 5. The alarm that should have signaled the valve’s opening in the control room did not trigger because one electrical supply line had been deliberately disconnected by EDF teams to secure the diagnostic operation. In this case, the issue was more organizational than technical. “This event had no impact on the safety of the installations,” EDF added. “The circuit was isolated, and chemical checks were carried out before the pump was put back into service.”

Once the valve works are completed, operational reactor tests will resume. Flamanville 3 is therefore expected to restart on October 1. The power increase will then be gradual, first reaching 60% of nominal capacity, then 80%, a step that will require authorization from the ASN. While EDF initially aimed for the Manche-based reactor to reach full power during the summer, the use of 100% of the EPR’s capacity will now only take place before the end of autumn 2025, at the latest one year after its connection to the French grid. ■