France’s reactor squeeze sends power above €300

The 20.4% figure in the headlines was a snapshot, not a summary. AFP calculated it from EDF's reactor notices before 10:00 on 12 August, the single moment when the largest share of France's nuclear fleet was classified as unavailable for environmental reasons (Europe 1, France 24). Some of those reactors kept producing at reduced power. The real economic story is what happened to prices when that lost output collided with peak demand.

Day-ahead electricity prices (what buyers pay today for power delivered tomorrow) jumped 21.8% in France to €142.50/MWh and 22.8% in Germany to €138.50/MWh (Euronext/Reuters, Oilprice). By evening, as solar generation faded and cooling demand held, same-day trading prices in both countries climbed above €300/MWh (The Edge).

13 reactors, two problems

Of France's 57 nuclear reactors, 13 were affected: eight fully stopped and five running below capacity (Euronews, Barron's).

The familiar problem was hot rivers. French nuclear plants pump river or sea water to cool their systems, then return it warmer. Environmental rules limit how hot that returned water can be, protecting fish and ecosystems downstream. When the Garonne hit 28°C, the Golfech plant had to cut back. At Chooz, near Belgium, low flow on the Meuse triggered a Franco-Belgian water-sharing agreement, and the reactor stopped entirely to preserve supply for downstream users in both countries (EDF Chooz, Franceinfo). Similar constraints hit plants on the Rhône.

The surprise was jellyfish. At Gravelines, France's largest nuclear site on the North Sea coast, a mass arrival blocked cooling-water intake pumps. EDF shut three units and reduced a fourth, pushing environmental unavailability past the previous record of 15.6% set just two days earlier (EDF, Le Figaro).

Scarcity in France, higher bills next door

Europe links national power markets through shared daily auctions, so scarcity in France can raise the price paid next door. When cheap nuclear drops out, more expensive gas-fired plants step in. The last plant needed to meet demand tends to set the market price for that hour. Gas can price the whole market even when most electricity comes from cheaper sources.

The squeeze tightened because German wind output fell to 4.7 GW, roughly 60% below the seasonal norm (Euronext/Reuters). Two of Europe's biggest low-cost power sources weakened at the same time, and evening solar disappeared on schedule.

The European Commission said on 11 August that the system remained stable, with interconnectors moving power toward tighter regions (European Commission). No country lost electricity supply. But keeping the lights on and keeping bills affordable are different things.

Dutch households on dynamic contracts, where the retail price tracks wholesale rates hour by hour, took the most direct hit (NL Times, Welingelichte Kringen). Italy, a large buyer of French power, saw available exports shrink during a similar June episode from around 10–12 GW to roughly 3 GW (DW). Romania's Cernavoda Unit 2 was already offline after Danube drought cut its cooling supply, tightening southeastern Europe separately.

On the winning side, gas plant owners and battery operators sold into those same high prices. Their fuel costs or stored energy didn't jump in the same hour, so the gap between what they paid and what they earned widened.

Small annual losses, expensive hours

EDF argues that climate constraints barely dent yearly output. The historical record supports this: losses stayed below 1% of French nuclear production in nearly every year from 2000 to 2022, reaching about 1.5% only in the extreme summer of 2003 (DW). The company plans to spend roughly €9 billion over 15 years adapting its fleet to rising temperatures (Le Monde).

But annual averages hide where the cost lands. It falls on households and businesses buying electricity during the specific hours when multiple reactors cut output at once. Annual nuclear losses can stay small while the market cost is large, because electricity gets expensive fast when low-cost supply disappears during peak demand. Whether EDF's adaptation spending actually reduces those peak-hour losses, or just limits total energy lost across the year, is something RTE (France's grid operator) and market data from future heatwaves will have to show.