Montel, citing EDF data, reported heat-related nuclear curtailment reaching 7.6 GW on Monday 3 August, 12 per cent of the French fleet and the steepest cut since the heatwave began the previous week 1. EDF forecasts an easing to 4.3 GW, 7 per cent, on 4 August, and 3 GW, 5 per cent, thereafter. EDF's own pages and those of grid operator RTE were unreachable on every route tried across two rounds of research, so read the figure as reported by Montel citing EDF rather than lifted from an EDF release.
River-cooled stations discharge warm water back into the watercourse, and French regulation caps both the discharge temperature and the effect on the river downstream. When a heatwave lifts the intake temperature, the only lever an operator has is to turn the reactor down. That makes the cut weather-shaped rather than calendar-shaped: it lifts when the rivers cool, not when a maintenance window closes. The same constraint took Chooz, Golfech and Bugey fully offline on 12 July , with Blayais and Saint-Alban on the watch list since earlier in the season.
The France-Germany day-ahead spread changed sign across the same window. Germany carried a premium of €16.41/MWh on Friday 31 July, €17.20 on Saturday 1 August and €5.47 on Sunday 2 August; on Monday 3 August France cleared a daily mean of 131.39 EUR/MWh, a French premium of €4.15 on the prints available 2. Three sessions earlier that same spread had been widening the other way .
This desk will not name a driver for the flip, because what is published cannot carry one. Curtailment peaked on the day the spread turned. Normalise every day to the same 00:00 to 06:00 UTC window, though, and at the exact transition French nuclear output rose by 1,202 MW while French wind fell 1,551 MW and French load rose 3,257 MW on the ordinary Sunday-to-Monday demand step 3. Both readings survive because they measure different hours: the 3 August generation series runs about six hours deep, while the price series runs 88 of 96 quarter-hourly prints. River temperatures peak in the afternoon, so a morning generation window structurally cannot see the curtailment Montel reports for the day as a whole.
A comparable river-temperature curtailment on 30 June removed a similar share of the fleet and left the spread pointing the same way it had before , and this desk has twice named the wrong driver on this pair: update #30 called a nuclear recovery when weekend demand and a doubling of French wind had done the work . French nuclear did fall a real and dateable amount earlier in the window, from a 41,954 MW daily mean on 31 July to 35,555 MW on 2 August 4, and that drawdown was already in the market on 2 August, when France still cleared below Germany.
