1,721,000 research outputs found
Verification, validation, and cross-comparison of tritium transport codes FESTIM, MHIMS, and mHIT
No full textTritium transport is a fundamental topic in the development of nuclear fusion reactors for sustainable and competitive energy production. Tritium breeding blankets and extraction systems must be as efficient as possible. Tritium handling systems are crucial to ensure fuel self-sufficiency, safe operations, and cost reduction. Component-level modeling supports design choices to build a more efficient system. In recent years, multiple component-level codes dedicated to simulating hydrogen Isotope transport mechanisms, such as permeation across materials and trapping, have been developed, verified, and validated. This work presents a comparison between three codes, MHIMS, FESTIM, and mHIT, in different verification and validation benchmarks, and their application on the ITER tungsten monoblock. The code comparison includes the V&V study for the mHIT code, and FESTIM results are compared against another code for the ITER monoblock in 2D and during transients. Indeed, to analyze and design tritium components for a fusion power plant, such as a breeder blanket, a plethora of features are necessary, such as trapping, 3 dimensions, multi-material interfaces, time-dependent transients, chemical reactions, and CFD coupling. The benchmarks showcased good agreement between the codes and experimental results. This work demonstrates the coherence and the solid common ground between the codes, verifies some features that are already implemented, and can serve as a starting point for more complex transport features (e.g., chemical reactions, convection, and turbulence coupling)
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
Transport dynamic of strontium in groundwater: Safety Assessment study
Full text linkOne of the activities of the Safety Assessment is the evaluation of the impact of a nuclear facility on the environment. The radionuclide transport into groundwater is subjected to different phenomena (e.g. groundwater dynamic, surface stream dynamic, the interaction between surface water and groundwater, radionuclide interaction with environmental matrix, etc.) that influence the risk of contamination of water. The investigation of the source term is fundamental to understand its impact on radionuclide transport. In this paper, in situ surveys and modelling were coupled to investigate the dynamic of strontium in an Italian nuclear site. On-site measurements have identified low quantities of strontium in monitoring wells, and through the modelling, the possible migration pathway of this radionuclide was identified. For a primary safety evaluation purpose, a parametric detailed analysis was carried out to identify which hydrogeological parameters and which artificial structure present in the area could influence the dynamic of strontium in the investigated site. In particular, the effect of the Cavour artificial channel on the strontium migration and dilution was demonstrated. The coupling of monitoring activities, periodically performed in the area, and the modelling activities, focused on the detailed relationships between the Cavour artificial channel and the underground water flow, contributes to better evaluate the possible radiological risk for population and environment and to support future safety studies
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
Radiological 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
Review of nuclear microreactors: Status, potentialities and challenges
Full text linkNuclear energy is being reconsidered worldwide as a low-carbon and dispatchable energy source. Following the development of Small Modular Reactors (SMR) to reduce the capital costs and increase the safety of new nuclear power plants, microreactors are being designed by several companies. Microreactors are usually defined as SMR with a power output in the range 1–20 MWe. They can operate as part of the electric grid, independently from the electric grid or as part of a microgrid to produce electricity and process heat. In the present paper, some microreactors at an advanced design stage are presented: eVinciTM, Aurora, Holos Generators, Xe-Mobile, NuScale, Sealer, U-Battery and Micro Modular Reactor. The main applications of microreactors and the technology features are then discussed to present the main potentialities and challenges. The main advantages are the small size, the simple plant layout and the fast on-site installation. The main challenges are the limited fuel availability, the security and proliferation risk and the licensing process. Finally, an economic analysis shows that, due to an economy of scale, despite the capital cost reduction, microreactors are not cost competitive with large nuclear plants, but they are competitive with technologies with similar scale and application, such as diesel generators and renewable sources in microgrids
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
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
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