 France's nuclear reactors comprise 90 per cent of EDFs capacity and so they are used in load-following mode and some reactors close at weekends because there is no market for the electricity.This means that the capacity factor is low by world standards, usually in the high seventies as a percentage, which is not an ideal economic situation for nuclear plants.During periods of high demand EDF has been routinely "forced into the relatively expensive spot and short-term power markets because it lacks adequate peak load generating capacity".