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The strategic path toward the safest possible nuclear power plants is to switch to inherently safe nuclear reactors, capable of self-shielding, without interference by man, in any accident situations. Examples of such plants are modular medium and low-power plants based on fast reactors with a breeding ratio close to one. As a result, in such plants the operational reactivity margin is less than/~eff, negative temperature feedbacks are present, the void effect of reactivity is negative, and the colloant is a liquid metal whose aggregate state remains unchanged in the entire operating temperature range and at the temperatures reached during accidents. The physical properties of such reactors eliminate reactivity accidents with runaway on prompt neutrons and the chain reaction is self-quenched in any accident.Liquid-metal coolant, combined with the single-unit construction of the plant, implementing passive cooldown (when all other possibilities are precluded) through the reactor vessel to naturally circulating atmosphere air, will make it possible to avoid destructive overheating of the core. This concept is being implemented in the USA in the projects ALMAR (PRISM and others) and in Russia in lead-cooled reactors, which are being developed by the Scientific-Research and Design Institute of Energy and Fuels [1], and in designs with lead-bismuth coolant, which are being developed by the Institute of Physics and Power Engineering and the Special Design Office "Gidropress" [2]. Japan has also started the conceptual development of such lead-cooled plants.The transition to lead-bismuth liquid-metal coolant, which is inert with respect to water and air, makes the concept of an inherently safe fast reactor more complete than the ALMR concept, which is based on sodium as the coolant.Mastery of Lead-Bismuth Alloy as a Coolant. Russia was the first to use and has unique experience in assimilating and using this coolant in application to moving power plants. The scientific development was directed by the Institute of Physics and Power Engineering and the engineering development was directed by the Special Design Office "Gidropress" and the Special Design Office for Machines.Work on the application of the eutectic alloy lead-bismuth was started in this country at the initiative and under the leadership of A. I. Leipunskii in 1952. The fundamental problems arising in the development of a nuclear power plant with such a coolant, including the questions of heat transfer, hydrodynamics, coolant technology, corrosion, mass transfer, and many others, were solved. The required experimental base, equipped with unique test stands, was created. Commercial and prototype nuclear power plants, on which operation, repair, and refueling of the reactors were perfected and preliminary service-life tests of the equipment were performed, were constructed. The total service life of a nuclear power plant with lead-bismuth coolant was -80 reactor.years.During this work skilled teams of investigators, designers, and operating personnel, capable of ...

Great interest has been observed in recent years in the accelerator-controlled (electronuclear) systems, where an intense source of neutrons, which consists of a target generating neutrons under the action of accelerated ions (usually protons), is placed in a neutron multiplying or/and moderating blanket.Development and substantiation work is being conducted with different intensities on such systems for three purposes. 1. Production of Energy Using the Uranium-Thorimn Cycle [1]. The blanket is a suberitical thermal or fast reactor with solid fuel. Reactivity accidents are ruled out on account of the suberiticality, and the use of uranium-thorium cycle greatly decreases the production of highly toxic actinides and plutonium, a potentially dangerous element from the standpoint of solving the problems of nonproliferation of nuclear weapons.2. Transmutation of Long-Lived Actinides and Plutonium Utilization. It is in this field that the supporters of suberitical electronuclear systems strive to prove their advantages over fission reactors. These arguments can be systematized approximately as follows.a) The large amount of accumulated plutonium, both reactor plutonium and weapons plutonium from disassembled nuclear warheads, make urgent the problem of utilizing it from the standpoint of nonproliferation of nuclear weapons and protection of the environment, since plutonium is a highly radiotoxic element. Weapons plutonium can be used as fuel in fast reactors, but on account of the presence of 238U any reactor produces plutonium.The subcriticality of an electronuclear system makes it possible to vary the composition of the nuclear fuel in the blanket over wide limits, and the system can operate on pure plutonium fuel.Some scientists, especially American scientists, believe that in the future nuclear power should operate with the minimum possible amount of plutonium, and subcritical setups have a niche in such a system. b) Transmuted actinides and fission products can be continuously introduced into and extracted from a subcritical system with liquid plutonium fuel, and a continuous chemical reprocessing can be organized at the same time. The total radiotoxicity of the fission products and actinides which are loaded into and produced in such a system can, in the opinion of specialists, decrease much more rapidly than in fast burnup reactors and therefore such a system is more efficient. c) For proton energies -1.5 GeV up to 50 secondary neutrons per proton are formed in a target consisting of a material with a high atomic number (lead, bismuth, and others), i.e., approximately 30 MeV of energy is released per neutron. At the same time, in the case of the fission of nuclear fuel about 80 MeV are released (-2.5 neutrons per fission event with energy release -200 MeV). This fact in principle makes it possil~le to achieve in the blanket of an electronuclear setup a higher neutron flux density than in a reactor, since the extraction of heat increases with the flux. In turn, higher fluxes make it possible to increase the trans...

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