The recent events at the Fukushima power plants (PP) have brought to light key issues which have to be discussed concerning the position of nuclear energy in the energy mix, in the context of global warming, of waning petroleum resources, of an increasing world population, and of its industrial development. These questions are addressed here from the viewpoint of physical facts; and, without proposing definite choices, this article aims to provide information on the equipment required to benefit from the fission chain reaction, while explaining the possible incidents and accidents, and the possible hidden military misuse of nuclear matter. Specific issues, such as risk assessment and risk management, will be considered, under the constraints of dealing with international non-proliferation safeguards and France energy resources independence. A special emphasis will be given on the fuel cycle, on the variety of time scales involved, and on the requirements of developing the next generation of nuclear power plants, and more specifically the fast breeder option. The lessons to be drawn from the Fukushima accident, resulting mainly from the residual power of used fuel and the loss of cooling source, are outlined, and the consequences to be drawn about the various relevant time scales are emphasized.