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The article presents the results of the calculation analysis of the criticality of the reactor pool compartment for VVER-1000 reactors at different stages of a severe accident. The criticality analysis of fuel-containing systems formed during the development of a severe accident is considered on the example of several discrete configurations that can be described by certain models. In reality, the course of a severe accident will be a continuous process of transition from the initial stage of the accident to its steady state at the end. However, depending on the fuel characteristics and conditions of development of a severe accident, any considered configuration of fuel assemblies and reactor pool materials may become final. The article presents a criticality analysis of the reactor pool compartment of the VVER-1000 reactor unit at the severe accident stages following the deformation of fuel rods and fuel assemblies at the initial stage of the accident due to water boil-off and temperature increase. On the basis of the models developed, the multiplication properties of the reactor pool compartment in the conditions of degradation of hexagonal tubes were investigated. Supercriticality (i.e. multiplication factor was greater than 1) was achieved in all two considered configurations of the water-uranium mixture. That is, under such conditions, the required level of subcriticality can be provided by a boron solution in water. The considered homogeneous single-layer and two-layer model of corium spreading on the support plate is safe in terms of criticality. However, the support plate has holes for the passage of the coolant to the fuel assembly. In the case when the melt or fuel debris enters the space under the support plate through these holes, they can form a uranium-water mixture with the remaining water, which at certain fuel and water ratios can become supercritical. In this case, the multiplication properties of the reactor pool compartment will depend on the ratio of impurities of the reactor pool and fuel assembly structural elements in the material under the support plate and/or the concentration of boric acid in the water. After damage of the reactor pool compartment floor, the melting of concrete begins. The considered configurations and material composition of the mixture of corium, concrete and water allow us to make a conclusion about the safety of this phase of a severe accident in terms of criticality.

The article reveals the latest trends in the modern development of the architecture of public centers in large cities, innovative methods of formation in the urban environment, defines their specificity and requirements, analyzes the features, patterns and modern design solutions in conditions of sustainable development. The relevance of this study is associated with the need for new systemic approaches in the formation of multifunctional facilities, taking into account modern urban planning concepts, which allow the formation of new types of public entities and become an important structural element of the urban environment. Turning to foreign experience in organizing multifunctional public centers, one can find that the main components of the architectural formation are their urban planning and the spatial organization of a favorable architectural environment. It is important to note this aspect: for the formation of large public centers in conditions of sustainable development, the following main trends are characteristic: the formation of a developed spatial organization - an architectural and compositional formation. Also a bright architectural and artistic image - a dominant in the urban environment, integration into the natural landscape - ecological direction of sustainable development, effective functional zoning, well-developed engineering infrastructure and communications. Thus, it has been determined that a multifunctional public center in the structure of a large city is a specific type of architectural object, which is formed into a single complex of spatial and planning elements that organize the core of the social and business life of this city.

The introduction of new fuel for nuclear power plants in Ukraine is related to obtaining a relevant license from the regulatory authority for nuclear and radiation safety of Ukraine. The same approach is used for spent nuclear fuel (SNF) management system. The dry spent fuel storage facility (DSFSF) is the first nuclear facility created for intermediate dry storage of SNF in Ukraine. According to the design based on dry ventilated container storage technology by Sierra Nuclear Corporation and Duke Engineering and Services, ventilated storage containers (VSC-VVER) filled with SNF of VVER-1000 are used, which are located on a special open concrete site. Containers VSC-VVER are modernized VSC-24 containers customized for hexagonal VVER-1000 spent fuel assemblies. The storage safety assessment methodology was created and improved directly during the licensing process. In addition, in accordance with the Energy Strategy of Ukraine up to 2035, one of the key task is the further diversification of nuclear fuel suppliers. Within the framework of the Executive Agreement between the Government of Ukraine and the U.S. Government, activities have been underway since 2000 on the introduction of Westinghouse fuel. The purpose of this project is to develop, supply and qualify alternative nuclear fuel compatible with fuel produced in Russia for Ukrainian NPPs. In addition, a supplementary approach to safety analysis report is being developed to justify feasibility of loading new fuel into the DSFSF containers. The stated results should demonstrate the fulfillment of design criteria under normal operating conditions, abnormal conditions and design-basis accidents of DSFSF components. Thus, the paper highlights both the main problems of DSFSF licensing and obtaining permission for placing new fuel types in DSFSF.

The paper analyzes US regulatory requirements for nuclear safety justification of the nuclear fuel management systems and their comparison with relevant Ukrainian requirements in order to define differences in using methodological and computer approaches that decrease the conservatism of criticality assessment of these systems without reducing the achieved level of safety.

Аналізуючи ядерну безпеку сховищ відпрацьованого ядерного палива з урахуванням вигоряння палива (burnup credit), необхідно враховувати розподіл вигоряння по довжині касети. Найпростіше та водночас консервативно можна прийняти вигоряння по довжині відпрацьованих ТВЗ однаковим й рівним середньому вигорянню на найменш вигорілих кінцевих ділянках. Однак це призводить до заниження вигоряння по касеті порівняно з реальним середнім значенням у 1,5—2,5 раза. Для зняття надлишкового консерватизму, закладеного в такому підході, пропонується метод консервативного врахування аксіального профілю розподілу вигоряння по довжині ТВЗ. Заснований на результатах аналізу аксіальних профілів розподілу вигоряння відпрацьованих ТВЗ, цей метод може використовуватися в обґрунтуванні ядерної безпеки систем поводження й зберігання відпрацьованого палива.

Впровадження нових видів палива, нових систем і механізмів, охоплюючи розроблені за межами України, на підприємствах української атомної енергетики пов’язано з отриманням дозволу (ліцензуванням) регулюючого органу України. У статті розглядаються проблеми, що виникли в процесі ліцензування сухого сховища відпрацьованого палива на Запорізькій АЕС, з питань ядерної безпеки, вивчаються шляхи їх вирішення і підбиваються підсумки ліцензування.

Як показав аналіз ядерної безпеки основних систем поводження з відпрацьованим паливом, не всі вони задовольняють вимогам нормативних документів. Проте подібну невідповідність не слід розглядати тільки як недоліки систем. Значною мірою це наслідок надлишкового консерватизму, закладеного в нормативних вимогах, який, в свою чергу, є наслідком недостатнього розвитку засобів моделювання процесів у ядерному паливі, може бути значно зменшений за рахунок більш точного моделювання паливних систем без зниження рівня ядерної безпеки цих систем.

Currently, WiMAX systems acquired widespread adoption, to help organize the network at MAN (Metropolitan access network) level. It is assumed that in the next decade, the performance of such systems can achieve 50 bits/second/Hz.This is due primarily to the fact that in MAN network large amounts of multimedia confidential information of high quality are transmitted. So it requires not only high speeds, but also the appropriate level of noise immunity. Therefore, the performance and noise immunity are the two main indicators of the radio system quality. The radio waves propagation (RWP) models in radio channel play a decisive role in their calculation. Several mechanisms of radio wave propagation are known, including the so-called street-wave channels (Fabricio, 2005) (Wei, 2007), that was already noted in the development of analog communication (Porrat, 2002). These channels are identified by the authors as wavelength channels formed by architectural buildings (WCAB) (Strelnitskiy, 2007). However, the existing mathematical models are extremely complicated, so they become ineffective in the calculation of large branching networks of urban and this fact makes it difficult to assess these characteristics. Performance is evaluated as the ratio of transmission rate to channel bandwidth and noise immunity is defined as the probability of a bit (BER) or packet errors (PER). The authors propose general approach to the WCAB representation in the form of microwave multipole.

The report concerns the main ways of increasing security of communication channels of digital communication systems for departmental communication networks at the physical level.