1,721,109 research outputs found
Technologically enhanced naturally occurring radioactive materials and radiation protection case studies
No full textThe building industry uses large amounts of waste products: in some cases, new construction materials with naturally or technologically enhanced levels of radioactivity (e.g. phosphogypsum, coal fly ash, oil shale ash, some rare minerals, etc.) are used. Most building materials contain naturally occurring radioactive elements, (K-40, Ra-226, and other ones). The presence of these radioisotopes can also cause exposure to Rn-222, Rn-220 and daughters. Increased interest in measuring radionuclides and radon concentration in building materials and indoors is due to health hazards due to this exposure in persons. Most individuals spend 80% of their time indoors and natural radioactivity in building materials is a source of indoor radiation exposure. Indoors-elevated dose rates may arise from high activities of radionuclides in building materials. In view of this, there is a need to develop and introduce in both international and national levels environmentally safe and economically reasonable standard regulations, which should be based on justified radiological, social and economical legislation concepts. Case studies on this problem, carried out in Greece and Italy, are reported to complete the discussio
Activation analysis of a compact Tokamak using Deuterium–Helium3 fuel
Full text linkRecent advancements in high-temperature superconducting (HTS) magnets have enabled tokamaks to reduce dimensions and operate with higher plasma parameters. This opens to the possibility of using advanced fuel mixtures such as Deuterium-3Helium (DHe3). Compared to traditional fuels, DHe3 offers the potential to reduce neutron-induced activation and minimize the presence of tritium in the fuel cycle. In a fusion reactor that uses a 50% Deuterium-50% 3Helium mixture, neutrons are produced solely in the Deuterium-Deuterium (DD) and Deuterium-Tritium (DT) side reactions, while Tritium can be produced during DD reactions and is therefore absent at the startup of the machine. This study proposes a comprehensive neutronic and activation analysis of a compact, high-field tokamak employing DHe3 fuel. Using OpenMC, an open-source Monte Carlo code, the feasibility and performance of this fuel mixture within the confines of a compact fusion reactor will be investigated. The activation analysis will be limited to the First Wall, Blanket and inboard Toroidal Field coils, with some simplifications in the tokamak layout. By analyzing neutron interactions and activation processes, as well as design modifications, we seek to assess the potential benefits and challenges associated with implementing DHe3 as fuel
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
ARC reactor – Neutron irradiation analysis
Full text linkNeutron irradiation is one of the most concerning issues to design plasma facing components and reactor inner structures in fusion devices, especially for high power density ones, like ARC reactor. This study addresses the main aspects of neutron irradiation on solid materials of ARC reactor. In particular it deeply analizes the effect of neutron induced activation proposing low activation structures, like vanadium alloys and different optimization methods like isotopic tailoring, detritiation and impurity control. Furthermore, irradiation damage issues and their dependence on the energy spectrum are highlighted. It resulted that V-Cr-Ti alloys dramatically reduce the radioactive inventory of ARC with respect to its baseline configuration, which proposes the application of Inconel 718. Such alloy is also optimizable through the tailoring of titanium isotopes and is virtually capable of hitting recycle limits in a couple of decades. Lastly, it shows a relatively growth of gas during irradiation. However, it is highlighted how experiments on neutron damage featuring fission neutrons risk to be able to tell very little about the behavior of the same materials under fusion neutrons, as damaging mechanisms seem to be different
Neutronic comparison of liquid breeders for ARC-like reactor blankets
Full text linkThe proposed blanket for Affordable Robust Compact (ARC) reactor is one of the simplest blanket concepts. It is a bulk tank filled with a lithium and beryllium fluorides molten salt. The fluid effectively works as tritium breeder, vessel coolant and neutron moderator and shield. However, despite the simplicity of the concept, the compactness of the reactor constitutes a novelty in the fusion field. It is thus necessary to evaluate all the possible solutions for an effective blanket component. This work analyses different liquid blanket identifying the most suitable for a compact fusion reactor. More specifically, the study addresses the capability of breeding tritium in a compact solution, actively shielding the coils and reducing the radioactive waste. Findings are that FLiBe optimizes the most the system in terms of applicability, tritium breeding, compactness and activation. Nonetheless, there is no lack of backup choices. For instance, there are hints that lithium-zirconium fluoride salts could accomplish the blanket main tasks in a compact reactor too. Leaving PbLi as inefficient, but cheap and still virtually viable solution
Development 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
Advanced fuel fusion reactors: towards a zero-waste option
No full textLow activation materials are only a partial response to the requirement of a really environmentally sound fusion reactor: another way round to tackle the problem is the reduction of the neutron flux and subsequent material irradiation, possibly by exploring other possible fusion reactions such as the DeuteriumHelium-3 one. Most of the studies and experiments on nuclear fusion are currently devoted to the Deuterium-Tritium (DT) fuel cycle. The recent stress on safety by the world community has stimulated the research on 'advanced' reactions, such as Deuterium-Helium-3 (DHe3). IGNITOR is a proposed compact high magnetic field tokamak. A design evolution of IGNITOR in the direction of a reactor using a DHe3 fuel cycle has led to the proposal of the Candor experiment. This paper deals with the radioactive waste issue for fusion reactors, proposing an innovative solution (the "zero-waste" option), which is a clear advantage of fusion power versus fission, in view of its ultimate safety and public acceptance. Fusion reactors with advanced DHe3 fuel cycle turn out to have quite outstanding environmental advantages
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
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