During a severe loss of coolant accident in a nuclear reactor, steam and hydrogen are produced by the oxidation of reactor core and get distributed in the containment. A water spray system is ...employed to cool the mixture as well as to enhance the mixing of the gases to avoid hydrogen accumulation. This paper presents two-phase numerical simulations of transient vaporization of a moving spherical water droplet. The numerical model considers the variation of thermo-physical properties in both liquid- and vapor-phases, as functions of temperature and species concentrations. Multi-component diffusion and surface tension effects are also considered. The model has been validated using experimental results available in literature for hydrocarbon fuel droplet evaporation. Validated model is used to study the evaporation characteristics of moving water droplets under conditions typically observed in nuclear reactor during a loss of coolant accident. The effects of ambient temperature and hydrogen concentration on the vaporization characteristics are studied thoroughly.
The prestress loss has a great influence on the integrity and tightness of the containment. As the service age of the containment increases, the prestress loss gradually increases. The operating ...experience of most nuclear power plants shows that the rate of prestress loss in the containment exceeds even the expected value of the initial design. At present, most scholars evaluate the prestress loss of the containment only at the end of the life of the containment, and there is little research on the safety performance of the containment under different internal pressure after the loss of prestress. From this, the whole life theory to the evaluation method of containment safety performance of nuclear power plants was introduced in this paper. The safety performance of the containment under different levels of internal pressure during the design basis period of 40 years and 60 years following the design basis period was evaluated, taking into account the prestress loss at various ages of the containment. The ABAQUS finite element software was used to create a refined three-dimensional finite element analysis model of the containment, prestress loss calculation based on Concrete Structure Design Code (GB 500102010) and application of prestressing in ABAQUS by the cooling method. The nonlinear finite element method was used to analyze performance indicators such as the yield of the steel liner, the yield of the prestressed tendons, and the evolution of concrete cracks. The findings reveal that when the containment concrete cracks and the steel liner fails, the internal pressure capacity that the containment can withstand is reduced after accounting for prestress loss, and the maximum equivalent plastic strain in the steel liner of the containment is concentrated at the top and bottom sides of the equipment hatch, the crack development of the containment concrete is also more serious than that without considering the prestress loss, and the crack development of the equipment hatch is changed from horizontal to oblique cracks. The deformation of the containment under the ultimate internal pressure is manifested by the outward expansion of the dome and the inward contraction of the equipment hatch. The dome of the containment is severely damaged under ultimate internal pressure. Containment’s deformation increases significantly after considering the prestress loss. However, the containment still has sufficient safety margin under the design internal pressure (0.4 MPa) after 40 years of design base period for containment service and consideration of extending service to 100 years. The above results have implications for the structural design and the assessment of life extension of containment.
Del en av denne fokusartikkelen sporer og feirer utviklingen i norsk Russlands-forskning de 35 årene. Del to introduserer spenningen mellom forskeren som analytiker og forskeren som kommentator og ...påpeker at vi ikke vet så mye om hvem debatten snakker til ut over det utenrikspolitiske miljøet selv. Del tre diskuterer hva slags standarder akademikere som opptrer som kommentatorer kan og bør holde seg med. Kommentatorer må ha mot, evne og vilje til å gi rom for andre stemmer. Kommentatoren må også forstå forskjellen på analyse, som krever ettertenksomhet, og kommentar, som skjer i kampens hete. En kommentatorisk siste del argumenterer for at Vestens politikk fremover bør være å demme opp for Russland, snarere enn å være ettergivende eller gå inn for regimeendring. Abstract in EnglishRussologists as PunditsPart one discusses the emergence of Russia studies in Norway over the last 35 years. Part two laments our lack of knowledge regarding who the receiver of comments by researchers actually are. Part three discusses dialogism, parrhesia and phronesis as qualities needed for a researcher to be a good pundit. The article ends with a defence for continuing a policy of containment towards Russia rather than shifting to the two alternative policies, which are appeasement and roll-back.
This paper presents a distributed adaptive finite-time control solution to the formation-containment problem for multiple networked systems with uncertain nonlinear dynamics and directed ...communication constraints. By integrating the special topology feature of the new constructed symmetrical matrix, the technical difficulty in finite-time formation-containment control arising from the asymmetrical Laplacian matrix under single-way directed communication is circumvented. Based upon fractional power feedback of the local error, an adaptive distributed control scheme is established to drive the leaders into the prespecified formation configuration in finite time. Meanwhile, a distributed adaptive control scheme, independent of the unavailable inputs of the leaders, is designed to keep the followers within a bounded distance from the moving leaders and then to make the followers enter the convex hull shaped by the formation of the leaders in finite time. The effectiveness of the proposed control scheme is confirmed by the simulation.
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•Understanding of the enzyme immobilization is required to optimize the processes.•Immobilization parameters and courses become critical to understand the process.•Changes in enzyme ...properties during immobilization can complicate the calculations.•Likely artifacts and problems to make these calculations are discussed.•Some advices to improve the understanding of immobilization processes are given.
Biocatalytic processes continue to find increasing application in industry. Therefore enzyme immobilization has also become of increasing importance as a means of allowing enzyme containment within reactors operating in continuous mode or else separation of enzyme after use in (fed-)batch reactors, as well as potential recycle. Whilst much has been reported in the scientific literature about enzyme immobilization methods, in many cases the protocol leads to losses in enzyme activity. In this review we outline the reasons for loss of activity during immobilization and highlight suitable diagnostic tests to elucidate the precise cause and thereby methods to restore activity. The need for standardized reporting of immobilization methods is also emphasized as a means of benchmarking alternative approaches.
The term Indo-Pacific has enjoyed growing popularity for years as a geographical and strategic construct. Increasingly, the Indo-Pacific is not conceived merely as a geographical construct, but also ...as a vital alternative to the Chinese “Belt and Road” Initiative (BRI). Conversely, Beijing views the debates over the Indo-Pacific as nothing more than an anti-Chinese containment strategy. Chinese criticism notwithstanding, the debate on the Indo-Pacific has gained traction within Europe, too. France promoted its own Indo-Pacific concept from 2018 onwards, followed by Germany in 2020 with their own Indo-Pacific Leitlinien (guidelines) that preceded the launch of the EU’s own Indo-Pacific strategy in 2021. To assess possible focus points of an emerging EU approach to the Indo-Pacific, this article evaluates strategic convergence and divergence between the so-called E2, France and Germany. It finds that Germany and France, despite their different role conceptions, converge with regard to their key objectives, planned initiatives and conceptualisations of regional order. The article also finds, however, that these contain, for the most part, very general declarations of interests and intent while also foregoing concrete strategic choices. It argues that any future EU approach to the Indo-Pacific is therefore likely to emerge around the least common denominator focus points, drawing on long-established EU approaches towards the Asia-Pacific, rather than a new, clear-cut EU approach to the Indo-Pacific.
•Effective heat capacity method simulates the PCM melting well.•Heat absorption mechanism of the PCM condenser is discussed.•PCM condenser design is optimized for nuclear safety.•Containment analysis ...is conducted when PCM condenser is used for passive cooling.•Performance of PCM condenser is evaluated compared to active spray system.
The new application of phase change material for passively cooling the containment building of a nuclear power plant provides many benefits such as minimized wall penetration, low maintenance cost, and the possibility of installation in currently operating power plants with a minimal design change. In this study, the applicability of PCM as a passive containment cooling system is verified through design and evaluation of the PCM condenser. In addition, the effective heat capacity method is verified for simulating the melting process of PCM in the condition of a reactor accident. The PCM condenser design is optimized with five design parameters; melting point, volume, heat transfer area, effective thermal conductivity, and total heat absorbed. The performance of the PCM condenser is evaluated by containment safety analysis and is compared to that of an active containment cooling system. Although the PCM condenser had a limitation for absorbing only a fixed amount of thermal energy due to the absence of an external heat sink, the PCM condenser shows better performance in the early stage after the accident initiation compared to the single spray system and finally maintains the integrity of the containment building.
Understanding the processes and mechanisms of the spatial spread of epidemics is essential for making reasonable judgments on the development trends of epidemics and for adopting effective ...containment measures. Using multi-agent network technology and big data on population migration, this paper constructed a city-based epidemic and mobility model (CEMM) to stimulate the spatiotemporal of COVID-19. Compared with traditional models, this model is characterized by an urban network perspective and emphasizes the important role of intercity population mobility and high-speed transportation networks. The results show that the model could simulate the inter-city spread of COVID-19 at the early stage in China with high precision. Through scenario simulation, the paper quantitatively evaluated the effect of control measures “city lockdown” and “decreasing population mobility” on containing the spatial spread of the COVID-19 epidemic. According to the simulation, the total number of infectious cases in China would have climbed to 138,824 on February 2020, or 4.46 times the real number, if neither of the measures had been implemented. Overall, the containment effect of the lockdown of cities in Hubei was greater than that of decreasing intercity population mobility, and the effect of city lockdowns was more sensitive to timing relative to decreasing population mobility.
•A city-based epidemic and mobility model is proposed for simulating the spatial spread of an epidemic between cities.•The effect of “city lockdowns” and “decreasing population mobility” measures were evaluated under ten scenarios.•The effect of decreasing returns to scale and distance decay of population mobility on the epidemic spread were found.
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