Heatwave forces EDF to shut three nuclear reactors in France, gas plants step in

France's state-owned utility EDF shut two more nuclear reactors on Thursday morning, bringing the total to three units offline because of the heatwave gripping the country. The reactor at Golfech in Tarn-et-Garonne had already been halted on Monday. The latest closures affect unit 3 at the Bugey plant on the Rhône river, stopped at 09:00, and unit 1 at Nogent-sur-Seine on the Seine, stopped at 09:15. EDF cited "external environmental causes" linked to compliance with river temperature limits designed to protect aquatic ecosystems.

Why reactors are shutting down

France's 57 nuclear reactors draw water from rivers or the sea for cooling. When river water is already warm because of a heatwave, discharging even slightly warmer cooling water can push temperatures past regulatory thresholds. At Golfech, the post-discharge river temperature must not exceed 28 °C. At Nogent-sur-Seine, regulations cap the temperature rise between upstream and downstream at 3 °C and the average downstream temperature at 28 °C.

The reactor number 3 at the Bugey plant on the banks of the Rhône has been shut since 9 o'clock, as has unit number 1 at Nogent-sur-Seine since 09:15 for external environmental causes, to respect the heating limits of the Rhône and the Seine.

Broader impact on production

The decision to stop or curtail reactors aims to protect river fauna and flora. Beyond the three fully halted units, the Saint-Alban plant in Isère is also affected: its number 2 reactor must reduce power output because of the high temperatures. EDF warned that production cuts are expected at other plants as the heatwave continues.

Gas plants fill the gap

The reactor shutdowns have triggered an unusual reliance on gas-fired power stations for a mid-summer period. Grid operator RTE stated on Wednesday that France has sufficient production capacity to meet electricity demand, even with these reactors offline. Experts cited in German reporting estimate that heatwave-related nuclear outages, which currently account for only 0.3 percent of national production, could rise to 1.4 percent of total output by 2035 as climate change intensifies extreme heat events.

The regulatory framework

All French nuclear plants operate under strict thermal discharge limits negotiated with environmental authorities. When river temperatures climb during heatwaves, EDF must reduce or stop production to avoid further warming. The cooling water discharged is typically warmer by only a few tenths of a degree to a few degrees, but in already heated waterways this can breach the legal thresholds. The current episode highlights the growing tension between France's nuclear-heavy electricity mix and the increasing frequency of extreme summer heat.