Nuclear Monitor #935

Jan van Evert, reporter WISE-Netherlands

The French state owned company EDF has published for the first time a report on the industrial and economic effects of increasing modulation of its fleet of nuclear reactors. It warns of the consequences of the increasing modulation due to the increase in electricity production by renewables such as wind and solar power and a stagnating electricity demand.

The nuclear power plants in France have been modulated since the eighties to help balance the electricity system. The reactors can adjust up to eighty percent of their power in thirty minutes, twice a day. If a modulation over eighty percent is desired, the reactor has to be shut down for at least 24 hours, which has happened frequently and increasingly.

But the phenomenon has changed dramatically in scale. Between 2019 and 2024, nuclear modulation volumes doubled, from around 15 terawatt hours (TWh) to over 30 TWh. In 2025 this was 33 TWh, nine percent of the total nuclear power production. And in 2028, the volume could peak at 42.5 TWh.

Because of the increased capacity of solar and wind power in France the variability of electricity production is much larger than in the past which is a challenge for the operation of the nuclear reactors. This leads to increasing maintenance costs for EDF because turbines, turbopumps generators etc. wear more  rapidly. The consumption of chemicals that are added to the water of the primary circuit also increases. These costs consist of 30 million euros per year per reactor for the turbines alone. At this moment, France has 57 nuclear reactors in operation which means that the total costs add up to at least 1.7 billion euros annually. But there’s another very obvious problem: less electric power produced means less money earned. EDF does not mention in its report how much money they lost because of this.

This situation is also caused by the third multi-year energy programme (PPE3) which provides for an increase in electricity capacity – particularly nuclear capacity – to consolidate the country’s energy sovereignty. But in the short-term the system is facing overcapacity. This is caused by the slow electrification of transport, building and industry.

Jan van Evert

Sources:
Full report (PDF, in French): https://www.edf.fr/sites/groupe/files/2026-02/2026_02_16_ETUDE_MODULATION.pdf
https://www.gazdaujourdhui.fr/nucleaire-edf-alerte-sur-le-cout-croissant-de-la-surproduction-electrique/
https://www.sfen.org/rgn/maintenance-organisation-adaptation-sept-enseignements-du-rapport-dedf-sur-la-modulation-nucleaire/