Because the European grid usually has less demand, more supply in summer and more demand, less supply in winter. This leads to EDF scheduling most maintenance a

Because the European grid usually has less demand, more supply in summer and more demand, less supply in winter. This leads to EDF scheduling most maintenance and refueling for nuclear power plants in summer. This year was particularly bad because the normal summer maintenances were accompanied by 1. a bunch of delayed maintenances that didn't happen due to COVID-19; 2. a potential issue with welds in a safety cooling system which was found in 12 of the more recent reactors and required some unplanned shutdowns to investigate and (sometimes) repair.