French Nuclear Exports Squeezed as Heatwave Limits River Cooling

⚡ AI Executive Summary

A June 2026 heatwave across Western Europe forced French nuclear reactors to reduce output as river temperatures approached regulatory limits for cooling-water discharge. Although France maintained its status as a net electricity exporter and domestic supply remained secure throughout the period, the afternoon export surplus compressed dramatically—from 11–12 GW early in the month to 2.9 GW on the hottest day—as rising demand collided with constrained nuclear capacity and depressed regional solar prices. This event reveals a structural vulnerability in European grid planning: river-thermal limits are becoming an increasingly common constraint on peak-hour nuclear availability precisely when regional electricity demand peaks. For neighbouring countries relying on French summer exports during evening hours, the relevant planning metric must shift from annual surplus capacity to the actual deliverable margin under thermal stress. As climate warming makes such heatwaves more frequent, the grid cannot treat nuclear river-cooling constraints as rare edge cases but must incorporate them into baseline system security assessments.