River heat forces three or more French reactors to stop or cut output at once in summer 2027
The test Between 1 Jun and 30 Sep 2027, three or more French nuclear reactors are shut down or run at reduced output at the same time for environmental reasons (river temperature or flow limits on cooling-water discharges), as stated by their operator or reported by AFP. The score is for an event set by river heat and discharge rules; Strature gives no view on any company.
Not under way · Confidence: medium · Reviewed 25 Oct 2026 · Scores from 1 to 10
This page answers: What could happen, how it is scored, and who is exposed?
Using this page
- Read the two scores: Likelihood and Impact are kept apart.
- Check what is happening, each fact with its source.
- Use the calendar for the dates to watch.
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Impact is the average of the four parts, rounded, plus one point when Canada is directly hit on two or more channels, up to 10.
Two separate scales from 1 to 10. Strature never multiplies or merges them.
What changed
Dated, newest first
- Impact 4 to 3.
Why it matters
French reactors on warm rivers must stop or cut output when cooling water would heat the river past legal limits. In July 2026 three reactors were shut and eight more cut at the same time, and heat losses for June and July reached about 3 TWh. A repeat in summer 2027 is a real prospect: a weeks-long squeeze on French output and exports, not a supply crisis.
Why Likelihood 6 Pushes: Golfech heat stops in 2019, 2024, 2025, 2026; Golfech shut and Bugey and Blayais cut in summer 2025; four Golfech stops and a three-reactor day in 2026; 2026 losses more than twice the long-run average. Brakes: weather; exemptions and the 30 C ceiling when the grid needs the plant.
Why Impact 3 Key price French spot power. One economy and its neighbours; days to weeks per stop; other reactors, hydro and imports at a cost.
The other facts on file (11)
- Heatwave of 17-30 Jun 2026: 72 departments on red alert on 25 Jun; national 24-hour mean above 30 C for the first time on 24-25 Jun. [6] (3 Jul 2026)
- Golfech 2 stopped 23 Jun (restart 2 Jul) and 9 Jul 2026 for a forecast 28 C Garonne; Golfech 1 in refuelling. [5] (9 Jul 2026)
- Golfech stopped again 29 Jul and 8 Aug 2026; the 2006 order caps the river at a 28 C daily mean, 30 C when RTE needs the plant. [4] (10 Aug 2026)
- On 12-13 Jul 2026 three reactors (Golfech 2, Bugey 3 and Chooz 2; unit numbers per NEI) were shut and eight reactors cut; Bugey exemption to 20 Jul. [2] (13 Jul 2026)
- The three units total about 3.65 GW, about 6% of a 61 GW fleet; EDF says heat losses averaged 0.3% of output since 2000; adaptation plan EUR 8.7bn over 15 years. [3] (14 Jul 2026)
- AFP: 3 TWh lost to heat in Jun-Jul 2026; Sfen: 2 TWh by 15 Jul; average about 1.2 TWh a year since 2006; France exported 51 TWh in H1 2026. [4] (10 Aug 2026)
- Spot price on 13 Jul 2026 about 114 EUR/MWh, evening peak 165; Selectra, citing Sfen, counted seven reactors cut; summer demand about 50 GW against 80-90 GW at winter peaks. [8] (13 Jul 2026)
- July 2026 average to mid-month 92.1 EUR/MWh (aggregator data, published 17 Jul), nearly 40% above June; Flamanville EPR stopped 16 Jul. [9] (17 Jul 2026)
- France's net exports in 2025 were 92.3 TWh: Italy 26.2, Germany-Belgium 23.1, Great Britain 22.6, Switzerland 20.1, Spain 0.2 (RTE Bilan electrique 2025, as reported). [7] (25 Feb 2026)
- In summer 2025 Golfech was shut and Bugey and Blayais cut output for heat. [10] (2 Jul 2025)
- EDF expects 2026 EBITDA about 10% lower, citing lower prices and heatwaves; nuclear estimate 350-370 TWh for 2026 and 2027; H1 2026 189.9 TWh. [1] (31 Jul 2026)
Where it sits
How it spreads
Between 1 Jun and 30 Sep 2027, three or more French nuclear reactors are shut down or run at reduced output at the same time for environmental reasons (river temperature or flow limits on cooling-water discharges), as stated by their operator or reported by AFP. The score is for an event set by river heat and discharge rules; Strature gives no view on any company.
Not under wayChannels 3 on the card
- French powerOutput falls for days to weeks at river sites; supply holds because summer demand, about 50 GW, is low against 80-90 GW at winter peaks [8].
- Regional pricesEvening spot spikes in France and neighbours, as on 13 Jul 2026 [8]; lower French exports to Italy, Germany-Belgium, Great Britain and Switzerland, which took most of the 92.3 TWh of 2025 net exports [7].
- RulesMore exemptions from discharge limits, as at Bugey in 2026 [2], and pressure on the EUR 8.7bn adaptation plan [3].
Sectors 1
- Energy and pipelines
Countries 1
- France primary
Who is exposed
- Countries
- France, Germany, Belgium, Switzerland, Italy, Spain, United Kingdom
- Sectors
- Energy and pipelines
Three scenarios and their signposts
- S1
A cool summer
One or two short stops, as in most years since 2000.
- S2
A 2026 repeat
Three or more reactors stopped together for days, evening price spikes, exemptions granted.
- S3
Heat plus outages
Heat cuts coincide with unplanned outages and French exports fall sharply.
| Path | Signpost |
|---|---|
| S1 | No red heat alert by mid-July 2027 |
| S2 | Golfech stops before 1 July 2027 |
| S3 | A second ministerial exemption in the same month |
No probability is given for the three paths.
Dates to watch
The dates to watch
A dot is a day, a bar a month or a year; a hollow mark is tentative. The line marks today.
- 1 Jun 2027 Scored window opens; Golfech summer heating cap applies to 30 Sep [4] Declared · Window
- Jul 2027 EDF half-year results with nuclear output [1] Tentative · Outside event
- 30 Sep 2027 Scored window closes [4] Declared · Window
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Connected in Strature
- France
- Drought cuts France's first wheat export outlook for 2027-28 by a fifth Shares a channel: The same heat and low river flow hit French farms and reactors.
- Switzerland orders power restrictions or quotas in winter 2026-27 Shares a channel: Switzerland relies in part on imported power; lower French exports touch both (Strature's view).
Sources
10 sources, numbered as the text cites them
- Résultats semestriels 2026. EDF · 31 Jul 2026 · Company · confidence high · retrieved 25 Oct 2026
- France powers down nuclear reactors over heatwave. AFP via eNCA · 13 Jul 2026 · News · confidence medium · retrieved 25 Oct 2026
- Extreme heat impacts French nuclear. Nuclear Engineering International · 14 Jul 2026 · Industry · confidence medium · retrieved 25 Oct 2026
- Golfech à zéro réacteur : une Garonne à 28 °C. IMEP-CNRS site · 10 Aug 2026 · Commentary · confidence medium · retrieved 25 Oct 2026
- EDF arrête Golfech : le seuil de 28°C paralyse le nucléaire. L'EnerGeek · 9 Jul 2026 · News · confidence medium · retrieved 25 Oct 2026
- Canicule de juin 2026 : un épisode historique. Météo-France · 3 Jul 2026 · Official · confidence high · retrieved 25 Oct 2026
- Bilan électrique RTE 2025 : la France bat des records. Selectra (reporting RTE) · 25 Feb 2026 · Industry · confidence medium · retrieved 26 Oct 2026
- Canicule 2026 : centrales nucléaires à l'arrêt ou à puissance réduite. Selectra · 13 Jul 2026 · Industry · confidence medium · retrieved 25 Oct 2026
- Le réacteur nucléaire le plus puissant de France à l'arrêt, ce que cela change pour votre électricité. Les Énergies Renouvelables (ECOinfos) · 17 Jul 2026 · News · confidence medium · retrieved 25 Oct 2026
- Why France shuts down its nuclear reactors during heatwaves. The Local France · 2 Jul 2025 · News · confidence medium · retrieved 26 Oct 2026
Reviewed 25 Oct 2026 · version 1 · last change: reviewed · All risks