This paper has been written on the base of Romerio, 1994, which includes 80 pages of references (here we only quote some of them which are particularly significant). A previous version has been published in Energy and economic growth: is sustainable growth possible? Proceedings of the 20th Annual International Conference of the International Association for Energy Economics: New Delhi: Tata Energy Research Institute, 1997, v. III, p. 845-856, We would like to thank the Swiss National Science Foundation who has partially supported this study, as well as Ms. Cheryl Dotti, Ms. Masha Egorova and Ms. Catherine Varfis for their remarks. We carry out an evaluation of the risks of nuclear policies from the point of view of security of energy supplies and of the environment, We define a model which helps to explain and evaluate the choice of the nuclear sector, electric utilities and governments. This model takes into consideration the main elements which may restrain nuclear energy development, in particular, electric consumption evolution, production costs, fuel resources, major accidents, disposal of highly radioactive wastes, and development of new technologies allowing to reduce emissions from the coal fired power station. We also examine the problem of the gap existing between "the reality" and "the objectives of the actors", because it allows to understand some energy policy decisions, We examine the risks provoked by energy strategies which try to realise their objectives through an unilateral technological choice. We point out the economic and political advantages of diversification and flexibility. We evoke the importance of objectivity and transparency, This paper intends to be a contribution to discussions on sustainable development and on the future of nuclear energy.