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The results of calculations of a high-capacity subcritical molten-salt reactor burning transplutonium elements and operating with a fast-intermediate neutron spectrum and the salt LiF-NaF-KF are presented.It is shown that this reactor makes it possible to burn ~300 kg/GW of americium per year, i.e., long-lived wastes from approximately 30 VVER-1000.To develop nuclear power and ensure its competitiveness with conventional and new power directions it is necessary to solve the problem of handling spent nuclear fuel, first and foremost, the long-lived radioactive wastes, specifically, the transplutonium actinides americium and curium. The two main concepts for utilizing them -storage or burning together with other actinides Pu, Np, and U in recycled fuel for fast reactors -have not yet reached technological maturity [1]. The OMEGA program [2] presumes that they are utilized in specialized reactors, preferably with minimal use of fissile materials, specifically, plutonium [3]. The choice of a specialized reactor remains a subject of discussion, and the molten salt reactor is a candidate. The advantage of a fast neutron spectrum for such a reactor has now been recognized [3]. Attempts to secure a fast neutron spectrum by using chloride salts have been unsuccessful because of their high corrosiveness, so that modern designs of molten salt reactors are based mainly on fluoride salts.Fluoride salts, unlike chloride salts, are compatible with construction materials, but to increase the fast-neutron fraction in their spectrum the solubility of actinides must be increased. Fuel salt with high solubility of plutonium and americium fluorides was unknown until recently, and for this reason data showing their high solubility in the eutectic LiF-NaF-KF [4] are critical (Fig. 1). These results were placed at the basis of the concept of subcritical molten-salt reactor for incinerating transuranium elements. The subcritical operating regime is due to the low fraction of delayed neutrons in the fission of 239 Pu (β = 0.22%), 238 Pu (β = 0.14%), 241 Am (β = 0.14%), and 245 Cm (β = 0.18%).The basic scheme of a conventional reactor for subcritical systems includes a target assembly, consisting of a channel for introducing a proton beam and neutron-generating target and surrounded by a subcritical molten-salt blanket where transplutonium elements are burned (Figs. 2, 3 and Table 1). The transmutation zone is surrounded by the first cooling loop, which includes the circulation pumps and heat exchanger, in which the same salt as in the reaction zone LiF-NaF-KF is used

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A cascade subcritical liquid-salt reactor designed for burning long-lived components of the radioactive wastes of the nuclear fuel cycle is examined. The cascade scheme of the reactor makes it possible to decrease by a factor of three the power of the driving accelerator as compared with conventional accelerator-blanket systems of equal power. The fuel composition of the reactor consists of 20% Np, Am, Cm, and other transplutonium elements and 80% plutonium, which are dissolved in a salt melt NaF(50%)-ZrF 4 (50%). For a 10 MW proton accelerator, 1 GeV proton energy (10 mA current) and subcriticality depth 0.05, the thermal power of the reactor is 800 MW, which permits burning ~70 kg/yr Np, Am, Cm, and other transplutonium actinides, i.e., service five VVÉR type reactors of equal power.The problem of handling radioactive nuclear wastes from nuclear power generation remains unsolved even at the strategic level. The only solution which has reached commercial implementation -burial in deep geological formationsis being challenged today [1]. Another (strategically more natural) solution to this problem -burning (transmutation) in fast reactors -can be implemented only after most of the thermal reactors are replaced by fast reactors, and it requires a long period of time [2]. The third route -the development of special burner reactors -has been under intense discussion in recent years but is still at the conceptual stage. The main difficulty of developing such reactors is the low fraction of delayed neutrons (β = 0.17%) with fissioning of Np, Am, Cm, and other transplutonium actinides, which makes it impossible to construct high-capacity and safe critical burner reactors, since the admissible fraction of the actinides in the fuel of such reactors does not exceed 3-5% [3,4]. Switching to subcritical systems with k eff < 1 eliminates this difficulty but requires an intense source of neutrons. In accelerator-blanket systems, the neutrons produced by a beam of accelerated charged particles (electrons, protons, deuterons) in a heavy target is such a source. Specifically, each proton with energy E ≈ 1 GeV creates ~20 neutrons in a lead target. The thermal power of the blanket (W b ) and the power of the driving accelerator (W a ) are related by the relation [5]

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