[en] This document proposes a synthesis of an assessment of additional investments which would be needed when phasing out nuclear, as well as a study of impacts in terms of increase of electricity production cost, energy transmission and energy bill. It also addresses questions raised by a massive use of renewable energies. Two scenarios are compared to assess the cost of replacement of the nuclear fleet, at constant consumption: keeping a high level of nuclear energy with the development of photovoltaic and wind energy, or phasing out nuclear with a carbon constraint (progressive closing down of nuclear reactors by 2025). The study is based on an economic modelling of the electric system according to some principles and hypotheses which are presented in appendix