Pressurised water reactors (PWRs) also offer the possibility of increasing operation beyond the natural cycle length by taking advantage of the power and coolant temperature reactivity coefficients. A decrease of reactor power and coolant temperature allows for a 30-60 equivalent full power days (efpd) extension beyond natural fuel cycle length. Only non-storable hydro-electrical capacity should be considered here. In the mid-1980s economic forecasts were calling for a moderate increase in energy demand for the coming years and for a substantial overcapacity of the French nuclear park. The nuclear energy was supposed to be the marginal for about 7 000 hours, i.e. for more than 80% of the year.