2019, Nevinitsa, V., Gusev, V., Smirnov, A., Volkov, Y., Гусев, Владислав Евгеньевич, Смирнов, Андрей Юрьевич, Волков, Юрий Николаевич

© 2019 Author(s). Nuclear power industry could be truly sustainable only under the condition of the Treaty on the Non- Proliferation of Nuclear Weapons. Thus, the issue of nuclear materials illicit diversion is crucial. One possible way to increase the resistance of the nuclear system to proliferation could be the increase of inherent security of nuclear materials used. One of the practical steps here could be the creation of intrinsic barriers in low-enriched uranium (LEU) fuel that is used in light water reactors worldwide. By the way, not only natural uranium could be used as raw material for such LEU, but also reprocessed uranium produced from spent nuclear fuel. In this study, proliferation resistance of enriched reprocessed uranium (in other words, commercial LEU made of reprocessed uranium) in the case of its covert diversion was analyzed. The conditions, under which this material could be turned into a direct use material in terms of IAEA was outlined. The scale of enrichment facility required to produce a significant quantity (SQ) of highly enriched uranium (HEU) throughout the duration of three months to two years, having the predetermined amount of diverted material (one SQ of LEU stolen from fresh fuel) was also assessed. Then, it was shown that such a feature of fuel made of reprocessed uranium as 232 U presence makes the detection of potential diversion possible even for much smaller quantities of LEU than in the case of fuel made of natural uranium.

2020, Gusev, V. E., Гусев, Владислав Евгеньевич

© 2020 Published under licence by IOP Publishing Ltd.This paper deals with the problem of reprocessed uranium (RepU) enrichment in cascades of gas centrifuges with simultaneous fulfillment of requirements on concentrations of isotopes 232,234,236U. These harmful isotopes bred by nuclear chain reaction are responsible for an increase in radioactivity level and neutron poisoning of fresh nuclear fuel. The study examines the cascade schemes that aim at closing the nuclear fuel cycle by satisfying the formal condition of the complete uranium reclaim. The prospective VVER fuel cycle strategy of multiple uranium recycling is considered. Schemes under consideration are multi-cascade ones. Such configurations are necessary to fulfill both a series of requirements on concentrations of even-numbered isotopes in commercial low-enriched uranium and condition of 'full return' of uranium extracted from spent nuclear fuel from particular reactor to produce fresh fuel load for the same reactor. The research provides a basis for comparison between three various multi-cascade schemes designed to re-enrich RepU under mentioned above conditions. The unified metrics (related to ordinary cascade and normalized to LEU product) of natural uranium savings, separative work, and depleted uranium consumption and their derivative, we used. The calculations take into account the necessity of RepU dilution to compensate for the adverse effects of 232,234,236U isotopes. As the reference cascade scheme, a simple modification of a single triple-flow cascade for RepU enrichment was considered. It is demonstrated that some modern cascade schemes could provide repetitious recycling of uranium.

2019, Nevinitsa, V., Smirnov, A., Gusev, V., Sulaberidze, G., Смирнов, Андрей Юрьевич, Гусев, Владислав Евгеньевич, Сулаберидзе, Георгий Анатольевич

© 2019 Author(s). Nuclear industry needs effective recovering of fissile material from used nuclear fuel, as uranium accounting more than 90% of the spent nuclear fuel (SNF) volume. Use of reprocessed uranium (RepU) is associated with the difficulties due to the presence of 232,234,236 U isotopes in its composition. The content of these isotopes in fresh fuel is limited in accordance with specifications for low-enriched uranium (LEU). In this regard, in order to make a product of the required quality, it is necessary to modify the regular cascade scheme for enriching natural uranium and/or partially dilute the RepU with raw materials not containing 232,234,236 U (for example, natural uranium or depleted uranium). To solve such problems, a number of cascade schemes have been proposed for the last decades. However, there is still no answer what kind of scheme is preferable. In addition, most of them are unsuitable for full reuse of uranium extracted from spent fuel. Within the framework of the present paper, a double cascade scheme is proposed that allows a full use of reprocessed uranium (of any composition, including "dirty" one) in fuel production in compliance with restrictions on even-numbered isotopes. The "quasi-ideal" cascade, widely used in modeling separation processes in cascades for the separation of multicomponent mixtures, was chosen as the object of this theoretical study. The physical regularities of mass transfer in the proposed cascade scheme are analyzed. The interdependencies of cascade parameters are studied. It is shown that this scheme can be effectively employed to enrich the RepU of "dirty" composition, which are typical for SNF after several irradiation cycles.