On August 12, EDF’s nuclear fleet recorded a 20.4 percent capacity shortfall when 13 of 57 reactors were affected by environmental constraints and a jellyfish swarm at Gravelines. France derives around 70 percent of its electricity from nuclear power, and power prices rose 22 percent that day. The event occurred during a 15-minute peak between 9:45 a.m. and 10 a.m. local time.