[Nuclear by the Numbers] Power and Availability: Two Key Indicators of the Fleet
As part of its “Nuclear by the Numbers” series, Revue Générale Nucléaire (RGN) highlights key energy issues through essential data insights. In this edition, we take a closer look at the available power of the French nuclear fleet, which experienced a remarkable recovery in 2024.
Just a few days ago, Étienne Dutheil, Director of EDF’s Nuclear Production Division, shared his satisfaction with the fleet’s performance during the 2024–2025 winter in a LinkedIn post. He wrote: “We delivered more than 50 GW of availability to the power grid — peaking at 56 GW in January — and operated our reactors with high reliability, achieving an availability factor of 85%.”
To assess the fleet’s performance, two main indicators are commonly used to measure its effective contribution to the electricity system: available power and availability.
Available power refers to the generation capacity that is either being injected into the grid or ready to be dispatched at any given moment, expressed in gigawatts (GW).
Availability is defined as the ratio between the number of hours a reactor is able to produce electricity and the total number of potential production hours, expressed as a percentage.
These two indicators are complementary but not equivalent. Moreover, it is important to note that availability calculation methods vary from one country or operator to another, meaning that international comparisons must be approached with caution.
2022: An Unprecedented Low Point
The year 2022 represented a highly unusual chapter for the French nuclear fleet, marked by historically low availability, which dropped to just 40% in August. Two major factors contributed to this situation:
- The emergence of stress corrosion cracking (SCC) on the safety injection system (RIS) and reactor shutdown cooling system (RRA) piping, particularly affecting N4-type reactors and several 1300 MW units. The need for extensive inspections led to prolonged shutdowns across multiple units.
- A backlog of maintenance operations stemming from the disruptions caused by the Covid-19 pandemic in 2020–2021 and the associated public health measures. This backlog placed a heavy strain on the industrial maintenance schedule.
2024: A Return to Industrial Performance
The year 2024 marked a turning point in operations, with a notable recovery in fleet performance. Annual electricity output reached its highest level since 2019, totaling 536.5 TWh — including 361.7 TWh from nuclear — allowing France to set a new record for electricity exports.
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The prioritized and phased resolution of SCC cases enabled the early return to service of affected reactors.
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The deployment of the START 2025 program (Safety, Technical expertise, Anticipation, Rigor, Transparency) structured a more industrialized approach to maintenance and strengthened the reliability of outage management processes.
2025: Intensified Operations Ahead
In 2025, the availability of the fleet may be temporarily adjusted due to an exceptionally busy industrial schedule. Étienne Dutheil explained: “Four scheduled outages for refueling and maintenance are planned, including four ten-year inspections, and eight outages during which we will carry out safety improvements, a steam generator replacement at Flamanville 2, and preparatory work for the fourth ten-year inspection (VD4) of the 1300 MW series.”■