[Flamanville EPR Series] Five Questions to Understand the First Steps of the New French Reactor

The pressure and temperature increases, divergence, power stages… The Flamanville EPR’s schedule for the coming months is packed as it prepares to fully power the national grid with low-carbon electricity.

On May 28, 2024, the French Nuclear Energy Society (SFEN) hosted an exceptional webinar on “Starting an EPR: the Loading.” The 241 fuel assemblies are now in place inside the Flamanville EPR’s vessel, and the lid has been sealed. The focus is now on starting the reactor and ramping up its power. Alain Morvan, Project Director of Flamanville 3, and Christophe Quintin, Chief Inspector at ASN, answered all questions regarding this process.

1. What is the schedule for the Flamanville EPR?

In his presentation, Alain Morvan did not commit to specific dates: “I absolutely want us to work with complete quality and safety,” he explained. However, the timeline is quite clear. Overall, the EPR Flamanville director mentioned a 7-month commissioning period. After loading from May 8 to May 15, the vessel was sealed. “We will gradually move towards completely filling the primary circuit,” he explained. The first step will be “ASN’s non-objection to the increase to 110 degrees, which is regulatory.” This will pave the way for divergence (the first nuclear reaction) in July 2024. The next step will be reaching 25% power, which again requires ASN’s green light and is scheduled to connect to the grid during the summer of 2024. A final regulatory milestone is set at 80% before reaching full power.

2. When will the first shutdown of Flamanville occur?

The first shutdown will occur after a predefined fuel wear rate. “There will be no cycle extension on the EPR’s first operating cycle,” Alain Morvan clarifies. The cycle duration is 385 EFPD (equivalent full power days). This leads to a shutdown towards the end of 2025, depending on the power levels achieved during the initial testing phases. The shutdown will primarily take place in 2026.

3. Why wasn’t the vessel lid replaced before startup?

Due to carbon segregation in the vessel lid, ASN requested its replacement. It will be carried out during the EPR’s first outage. EDF has been authorised to complete a full cycle with the original lid. The future Flamanville lid is currently being finished at Framatome’s Chalon facilities. There are still elements to finalise on the manufacturing and regulatory aspects to ensure it is “compliant with safety requirements, with its conformity certification,” Alain Morvan and Christophe Quintin explain. The new lid will be made available to EDF during the second half of 2024. Once delivered to the Flamanville plant, it will still undergo a preparation phase before being introduced into the reactor building. “The need for energy production for France meant that we were not going to wait several months for the lid to be available before starting up,” explains Alain Morvan.

4. How were the lessons learned from the turbine of the Olkiluoto EPR in Finland considered?

There’s no real basis for comparison regarding the turbine, as they are not the same models, explain the two experts. In Flamanville, it involves the Alstom Arabelle turbine – now owned by General Electric – which is well known in France. In Finland, a Siemens turbine experienced difficulties. Nevertheless, these issues have been studied in preparation for the start-up of the Flamanville EPR and to bolster the technical expertise of EDF’s teams.

5. The Taishan-1 EPR experienced issues related to fuel assemblies. How is this addressed in France?

The phenomenon of neutron flux fluctuation in the core of the EPR is a phenomenon already observed in reactors in France but of low amplitude. This comes from variations in the water blades circulating inside the core between the assemblies. The causes are understood, and the proposals made to ASN to address this phenomenon have been validated. A second phenomenon identified at Taishan was fuel degradation. This was related to the grids that hold the fuel rods. EDF has conducted a specific thermal treatment on the grids of the 64 assemblies located on the periphery of the Flamanville EPR core. This required remanufacturing a series of assemblies with these modified grids “to eliminate any risk of spring breakage that holds the fuel rods in case of under-exposure to neutrons,” explains Alain Morvan. A third phenomenon encountered was the corrosion of the fuel claddings. This has already been observed in the French nuclear fleet and corrected with an evolution of the alloys used. In China, weaknesses have been identified. Indeed, at each outage, the assemblies are individually scrutinised to detect any signs of oxidation, and measurements are conducted using instruments to assess the oxidation rate. For the new Flamanville fuel, there will be no problems during the first cycle, and the assemblies will be meticulously inspected during the first outage.■

Par Ludovic Dupin (Sfen)

Image : Flamanville EPR – ©EDF