New aspects of the development of a future nuclear power system based on the advanced technologies of a closed nuclear fuel cycle with fast-neutron reactors are discussed on the basis of an analysis of systems problems pertaining to present-day nuclear power. The systems requirements ensuring adequate fuel for nuclear power with any installed capacity and maximum use of natural uranium and thorium brought into the fuel cycle are formulated. Sodium-cooled fast reactors, which thus far possess the highest level of technological readiness for commercialization, are given a special role in the formation of a new technological platform for large-scale nuclear power of the 21st century.Present-day nuclear power, which provides up to 16% of the total production of electricity, plays an appreciable but by no means the main role in the energy system of our country. Meanwhile, the growing ecological, economic, and geopolitical problems that dominate energy production based on fossil fuels today require finding ways to increase the role of nuclear power substantially with it becoming one of the main sources of energy in the third millennium. Atomic energy can and must serve the needs of our country for electricity as well as in other applications: heat supply, water desalination, hydrogen production, automotive fuel, and others.Systems Questions. Thermal reactors and open-fuel-cycle technology are used in our country and throughout the world. Nuclear power plants with thermal reactors are supplied with fuel on the basis of technologies for obtaining natural uranium and enriching the uranium so obtained to fabricate uranium fuel; the primary means for handling spent is temporary storage. The nuclear power plants built and operated today are safe and ecologically attractive and, with no postponed problems, they generate electricity competitively.However, the modern technological platform * of nuclear power is of "military" origin, since some of the key technologies which enter this platform were initially developed as part of highly militarized programs. On the basis of well-known considerations of scientific-technical, economic, ecological, and political (nonproliferation) nature, it is impossible to develop large-scale (ten thousand GW) future nuclear power on this platform. Two basic systems shortcomings prevent doing so: low utilization efficiency of the natural raw material and the enormous amounts of wastes produced per unit of useful production. The search for ways to overcome these obstacles relies on the ideas of expanded production of fuel and the physical principle of fast power reactors, ideas which were independently formulated by the eminent physicists E. Fermi in the USA and A. I. Leipunskii in the USSR back in the 1940s [1].In our country, the scientific, design, and technological work performed to realize these ideas has been ongoing for more than half a century [2][3][4]. The research is aimed at developing nuclear technologies which are capable of full utiliza-* A technological platform is a genetically (wi...