EPR Flamanville Series: Reactor Divergence – The Heart of the Flamanville EPR Finally Beats

The EPR has officially diverged, meaning the first chain reaction has commenced within the reactor core. Four months after being loaded with fuel, EDF can now proceed with the power ramp-up of the most powerful reactor in the French fleet. The reactor will be connected to the grid by the end of autumn.

At 3:54 PM on Tuesday, September 3, the entire French nuclear sector breathed a sigh of relief. After a challenging construction period, the Flamanville EPR officially diverged. This means that its nuclear core is now pulsating to the rhythm of uranium atom fission and a neutron flux. This milestone was made possible after receiving authorization from the ASN (French Nuclear Safety Authority) the day before (September 2), with operations undertaken by EDF teams starting at 9 PM. This marks the first reactor startup in France in 25 years.

“With the divergence, meaning the reactor ignition, we have crossed the most significant step in the startup of Flamanville 3. All EDF teams are focused on conducting the startup safely, in close cooperation with the safety authority,” stated EDF CEO Luc Rémont soberly. In a statement, EDF noted that “Flamanville 3 enters the ‘reactor in production’ phase.”

Towards 25% Power and Grid Connection

In an educational video on YouTube, EDF simply describes the mechanism of divergence. While the fuel was loaded into the reactor last May, it was kept dormant by absorbing neutrons, thanks to a high boron content in the primary circuit water and the lowering of the control rods. By reducing the boron content and raising the control rods, the neutron flux increased until a “stable and continuous” chain reaction was achieved. In these first moments, the reactor operates at a minimal power level. Régis Clément, Deputy Director of the Nuclear Production Division, speaks of “0.1 or 2% of the reactor’s nominal power.”

From this moment, and throughout its power ramp-up, the reactor will be scrutinized in every detail by EDF and the ASN teams. In a statement, the ASN wrote: “The ASN will oversee the subsequent startup phases of the reactor, up to reaching its nominal power. In particular, EDF will need to seek ASN’s approval to exceed certain power ramp-up milestones.”

The reactor will reach several power levels, each requiring ASN’s approval to proceed. The first milestone will be achieving 25% power, at which point the reactor will be connected to the national electricity grid. This milestone is expected by “the end of autumn,” assures EDF. A significant testing program will then be conducted on both the nuclear and conventional parts of the reactor. The second milestone will be at 80% power, before reaching the reactor’s full capacity.

Increase in Nuclear Production

If by the end of the year, the EPR reactor will contribute to the national park’s overall production, EDF is concurrently pleased with the excellent performance of the existing fleet. The company has revised upwards its production estimate for 2024, now expected between 340 and 360 TWh, up from the initially forecasted 315 to 345 TWh (not counting the EPR). This is due to the good performance during outages and the control and repair of the stress corrosion cracking phenomenon. ■