This paper investigates the role that nuclear fission energy could play in assuring a reliable energy supply, in a sustainable development scenario with the aim to limit the global warming rise to +2 °C. Reference to scenario "IPCC IS92a, Business as Usual" will be used and kept out with the history of the world primary energy consumption from 1970 to 2005. Besides, in the medium-long term, growing fission nuclear energy rates are hypothized from 29.3 EJ (ExaJoule) in 2005 to about 400- 500 EJ by the end of the century. This would entail generating about 80% electricity by nuclear power sources. This aim is within reach of today's day nuclear technology and has already been attained in France. Technological innovation and the free markets are pushing us towards a global economy; in this context nuclear power could enlarge its range and be used for large powered ships, see water desalination, cogeneration, hydrogen production, electric rail roads and domestic use. On the basis of the scientific and technological know how one can evaluate energy supplies that, by the end of the century, could lead to the transition from thermal nuclear fission reactors to fast nuclear fission reactors. Such reactors allow a more efficient use of nuclear fuel of about 160 times more than thermal reactors, and the extractable energy from raw materials is 160 times higher. Parametric studies have allowed to evaluate uranium use both for thermal and fast reactors on the basis of the present inventory of uranium resources. Even if we were to imagine costs 10 times higher than today's price of the spot market, results show that the impact of nuclear fuel has been evaluated for final cost of electricity generation that is not 3-4% higher than total cost.