1,721,037 research outputs found
A neutronics optimization approach for preliminary design and safety of nuclear reactors for nuclear thermal propulsion
Full text linkNuclear thermal propulsion is a key technology for long-range spaceflight, as demonstrated by the rising interest from space agencies, especially NASA. A preliminary design involves the exploration of many reactor configurations, until a configuration that meets all the design requirements is found. Trade-offs among different design fields, such as neutronics, thermal-hydraulics, safety and rocket performances are unavoidable. Design engineers have to run a large amount of simulations because of the multitude of possible reactor configurations and the different analyses that must be carried out. The present work investigates an optimization approach for the design of a LEU reactor with CERMET fuel, to find a configuration that fulfils neutronics, safety and NASA requirements for a nuclear thermal rocket. A neutronics analysis constitutes the basis of the work, but accidental scenarios and thermal-hydraulics analysis are performed as well, to assess reactor safety and rocket performances. The optimization procedure simulates different configurations and gradually reduces the design space to be explored, until an optimal region is found. In this way, unnecessary simulations are avoided. A Python script is developed to handle the whole analysis, from pre-processing to post-processing, including the integration between the neutronic code Serpent and MATLAB®. Once the optimal region is found, the most promising configurations are identified by comparing different performance metrics retrieved from the neutronics analysis. A safety analysis that simulates the reactor behaviour in four accidental scenarios is carried out on this smaller group of reactor configurations. Finally, reactors that fulfil safety requirements undergo a thermal-hydraulic analysis, which verifies that thermal limits are not exceeded and evaluates rocket performances. The approach successfully reduces the number of configurations to explore, and limits additional analyses to those configurations that are truly competitive. Furthermore, configurations in the optimal region achieve better performance than the initial configuration. It is also found that the most demanding constraints relate to safety: many promising configurations were discarded because they cannot meet safety criteria. This highlights the necessity of including safety analyses in the initial phase of reactor designs. It is concluded that a LEU, CERMET-fuelled reactor design can be considered challenging but feasible, and the approach presented in the work may be applied to find an optimal configuration for a preliminary reactor design
Gestione digitale della gara di appalto: integrazione delle modalità di aggiudicazione con la metodologia BIM
No full textRadiological source terms estimation for the Divertor Tokamak Test (DTT) facility
Full text linkThe Divertor Tokamak Test (DTT) facility will start its operations in 2026. DTT will operate with D-D fuel only, for an expected operational period of 25 years. Nevertheless, tritium will be produced by the D(d,p)T reaction. A mandatory step in the safety assessment of the machine is the estimation of the different source terms. Major contributions to the source terms are due to tritium and to activated dust. The amount of tritium in the vacuum chamber, in co-deposited tungsten layers and implanted in the bulk of the first wall is computed in this work. Also, a preliminary estimation of dust production due to inter and intra ELMs sputtering is carried out. Results report small amount of source terms related to tritium, below 1 mg after one year of full power operations, and less than 300 g of activated dust at the end of life
Design and simulation of a fuzzy supervisory control system integrated in a small public building
Full text linkDevelopment of an object-oriented, thermal-hydraulics model for ARC FLiBe loop safety assessment
Full text linkThe development of new fusion reactor concepts is a challenging task for designers and safety analysts. Little information is usually available from previous experiences or experimental campaigns, especially when the design is innovative. Hence, system modeling is of fundamental importance. A proper system model should allow the investigation of different design options, and a preliminary assessment of the relative safety features. Anticipated or accidental transients can be studied, exploring the design space and highlighting possible criticalities. Object-oriented modeling is extremely advantageous to carry out this task. ARC pre-conceptual design (MIT-PSFC) may greatly benefit from this kind of analysis. A 1-D system-level, thermal-hydraulics model of ARC FLiBe loop developed in Modelica language is presented in this work. Because of the innovative nature of ARC design, most of the components are not available in the Modelica standard library. Thus, the key components of the loop are defined and modeled. No experimental results are currently available for model validation; therefore, the model consistency is assessed by verification and benchmark against analytical and numerical models. A Python wrapper is developed to explore multiple transient conditions by automating pre-processing and post-processing. Component failures are injected in the thermal-hydraulics model by a Monte Carlo routine. It is found that the model can efficiently describe different transients, with a low error on key parameters (pressure drop, fluid temperature). Furthermore, the model can be easily adapted to different design, thanks to the modular structure of object-oriented models. Similarly, it can be implemented in broader applications for safety analysis by coupling with suitable soft computing techniques
Development of an Advanced-Fuel Nuclear Fusion Experiment
No full textAs a first step to exploring the possibilities of D-3He plasmas, a deuterium-tritium burning plasma experiment at high field and plasma densities, which can be much closer to the required parameters than present-day experiments, is particularly attractive. Compact high-field experiments were the first to be proposed in order to achieve fusion ignition conditions based on existing technology and the known properties of high-density plasmas. In previous studies, a feasibility study of a high-field D-3He experiment of larger dimensions and higher fusion power than Ignitor, but based on Ignitor technologies, was brought to the proposed Candor fusion experiment. Unlike Ignitor, Candor would operate with values of poloidal beta around unity and the central part of the plasma column in the second stability region. The toroidal field coils are divided into two sets of coils, and the central solenoid (air core transformer) is placed between them in the inboard part. In this paper, a revised design of Candor is proposed, based on the new technologies. This tokamak is capable of reaching D-3He ignition on the basis of existing technologies and knowledge of plasma, without any optimistic extrapolation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Structural and functional alterations of cellular components as revealed by electron microscopy.
No full text"Scanning (SEM) and transmission electron microscopy (TEM) are two fundamental microscopic techniques widely applied in biological research for the study of ultrastructural cell components. With these methods, especially TEM, it is possible to detect and quantify the morphological and ultrastructural parameters of intracellular organelles (mitochondria, Golgi apparatus, lysosomes, peroxisomes, endosomes, endoplasmic reticulum, cytoskeleton, nucleus, etc.) in normal and pathological conditions. The study of intracellular vesicle compartmentalization is raising even more interest in the light of the importance of intracellular localization of mediators of the signaling in eliciting different biological responses. The study of the morphology of some intracellular organelles can supply information on the bio-energetic status of the cells. TEM has also a pivotal role in the determination of different types of programmed cell death. In fact, the visualization of autophagosomes and autophagolysosomes is essential to determine the occurrence of autophagy (and also to discriminate micro-autophagy from macro-autophagy), while the presence of fragmented nuclei and surface blebbing is characteristic of apoptosis. SEM is particularly useful for the study of the morphological features of the cells and, therefore, can shed light, for instance, on cell-cell interactions. After a brief introduction on the basic principles of the main electron microscopy methods, the article describes some cell components with the aim to demonstrate the huge role of the ultrastructural analysis played in the knowledge of the relationship between function and structure of the biological objects
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