1,720,976 research outputs found
ALFRED: A revised concept to improve pool related thermal-hydraulics
No full textALFRED, namely the Advanced Lead-cooled Fast Reactor European Demonstrator, has been conceived to serve the industrial deployment of the Lead-cooled Fast Reactor (LFR) technology. ALFRED is a demonstrator reactor designed with the specific purpose to test and qualify innovative components and procedures to be used in commercial reactors. In its role of European Technology Demonstrator Reactor, it will offer a representative operational environment of interest for research organizations, industry and safety authorities. Initially developed as part of a collaborative effort funded through the European 7th Framework Programme, the project was taken over by an international consortium Fostering ALFRED Construction (abbreviated to FALCON). As one of the priorities of the consortium Expert Board, the ALFRED design underwent an in depth review, aimed at identifying and addressing vulnerabilities in terms of reliability and safety, investigating also scalability of the design, flexibility for maintenance and replacement, manufacturability of components, availability of codes and standards for nuclear components and materials. The reactor coolant system arrangement was found susceptible to two main thermal-hydraulic issues typical of Fast Reactor (FR) pool-type designs: (i) thermal stratification in the upper part of the pool and (ii) potential steam entrainment in case of Steam Generator Tube Rupture or leakage. Moreover, (iii) the risk of lead freezing, more specific to the use of high melting point metals as coolants, represented a third issue, of particular concern in conjunction with the passive residual heat removal function in accident conditions.Starting with a general description of the ALFRED Project framework, including the experimental facilities in support to the LFR Research, Development and Qualification plan, the paper will focus on the new system arrangement and Decay Heat Removal (DHR) system of the ALFRED concept design, aimed at improving the pool thermal-hydraulics against the above described issues and risks. Since the ALFRED revised configuration is considered to offer improved safety and robustness, the FALCON consortium is willing to share the outcome of private and national investments, with hope of stimulating new opportunities for further developments and investigations through advanced computational tools and experimental tests within the LFR research community
THEORETICAL AND NUMERICAL INVESTIGATION OF THREE DESIGNS FOR A PRIMARY CIRCULATION PUMP EVOLVING LIQUID LEAD FOR GEN-IV REACTORS
No full textSicurezza e sostenibilità dell’energia nucleare da fissione: reattori veloci refrigerati a piombo
No full textL’impiego pacifico di energia nucleare, ad oggi basato sullo sfruttamento di neutroni termici e combustibile arricchito in
Uranio-235 refrigerato ad acqua, ha ben risposto alla crescente domanda di energia elettrica cui assistiamo da alcuni decenni.
Tuttavia, sebbene gli standard di sicurezza già raggiunti nel settore siano sicuramente i più elevati nel mondo industriale, con i
reattori attualmente operanti, le riserve di combustibile attualmente conosciute e la quantità di rifiuti nucleari attualmente
prodotta, la sostenibilità a lungo termine di questa fonte di energia, nel modo in cui oggi viene impiegata, è un qualcosa su cui
riflettere.
I reattori di “quarta generazione” potrebbero rappresentare la valida risposta alla richiesta di un’energia nucleare da fissione
che sia più sostenibile. Fra questi, appare particolarmente promettente il reattore a neutroni veloci refrigerato a piombo liquido
(LFR). La progettazione di un reattore LFR dimostrativo europeo (denominato “ALFRED”) è la sfida raccolta dal progetto
europeo “LEADER”, coordinato da Ansaldo Nucleare S.p.A..
Il presente articolo riassume i vantaggi offerti dai reattori LFR, descrive il reattore ALFRED e mette in evidenza i temi su cui
concentrare i futuri sforzi della ricerca internazionale
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
CFD pre-test analysis and design of the NACIE-UP BFPS fuel pin bundle simulator
No full textIn the context of GEN-IV heavy liquid metal-cooled reactors safety studies, the flow blockage in a fuel sub-assembly is considered one of the main issues to be addressed and one of the most important and realistic accident for Lead Fast Reactors (LFR) fuel assembly. The blockage in a fast reactor Fuel Assembly (FA) may have serious effects on the safety of the plant leading to the FA damaging or melting. The temperature of the coolant leaving the FA is considered an important indicator of the health of the FA (i.e. the effective heat removal) and is usually monitored via a dedicated, safety-related system (e.g. thermocouple). The external or internal blockage of the FA may impair the correct cooling of the fuel pins, be the root cause of anomalous heating of the cladding and of the wrapper and potentially impact also fuel pins not directly located above or around the blocked area. In order to model the temperature and velocity field inside a wrapped FA under unblocked and blocked conditions, detailed experimental campaign as well as 3D thermal hydraulic analyses of the FA is required. The present paper is focused on the CFD pre-test analysis and design of the new experimental facility 'Blocked' Fuel Pin bundle Simulator (BFPS) that will be installed into the NACIE-UP (NAtural CIrculation Experiment-UPgrade) facility located at the ENEA Brasimone Research Center (Italy). The BFPS test section will be installed into the NACIE-UP loop facility aiming to carry out suitable experiments to fully investigate different flow blockage regimes in a 19 fuel pin bundle providing experimental data in support of the development of the ALFRED (Advanced Lead-cooled Fast Reactor European Demonstrator) LFR DEMO. In particular, the 'Blocked' Fuel Pin bundle Simulator (BFPS) cooled by lead bismuth eutectic (LBE), was conceived with a thermal power of about 250 kW and a uniform wall heat flux up to 0.7 MW/m2, relevant values for a LFR. It consists of 19 electrical pins placed on a hexagonal lattice with a pitch to diameter ratio of 1.4 and a diameter of 10 mm. The geometrical domain of the fuel pin bundle simulator was designed to reproduce the geometrical features of ALFRED, e.g. the external wrapper in the active region and the spacer grids. Pre-tests calculations were carried out by applying accurate boundary conditions; the conjugate heat transfer in the clad is also considered. The numerical simulation test matrix covered the envisioned experimental range in terms of mass flow rate; the wall heat flux was imposed in order to have a fixed temperature difference across the BFPS in unblocked conditions. The blockages investigated are internal blockages of different extensions and in different locations (central sub-channel blockage, corner sub-channel blockage, edge sub-channel blockage, one sector blockage, two sector blockage). High resolution RANS simulations were carried out adopting the ANSYS CFX V15 commercial code with the laminar sublayer resolved by the mesh resolution. The loci of the peak temperatures and their width as predicted by the CFD simulations are used for determining the location of the pin bundle instrumentation. The CFD pre-test analysis allowed also investigating the temperature distribution in the clad to operate the test section safely
Coarse-mesh thermal-hydraulics and neutronics coupling for the ALFRED reactor
No full textAmong the six advanced reactor systems identified by the Generation IV International Forum, the lead fast reactor (LFR) has been considered as one of the most promising future nuclear power plants. Among the LFR designs, Ansaldo Nucleare, as coordinator of the Lead-cooled European Advanced DEmonstration Reactor project, proposes Advanced Lead Fast Reactor European Demonstrator (ALFRED) as LFR demonstrator, which is the study object of the present paper. A multiphysics model for the ALFRED core is developed and presented in this paper, which couples neutronics and thermal hydraulics. The first physics is solved with neutron transport Monte Carlo simulations, while temperatures and the lead density are updated with coarse-mesh-based finite volume method CFD runs. The proposed model focuses on the adoption of spatially non-uniform temperature distributions of materials to compute better on-the-fly estimations of nuclides cross sections and thence a more accurate neutron physics description
ALFRED reactor coolant system design
No full textLead-cooled fast reactors represent the forefront of Generation IV reactor concepts thanks to the technological development that has taken place over the last 20 years. Lead technology is object of steady attention in many Countries thanks to several development projects and an exponentially increasing industrial interest in recent years. One of the most advanced European projects is focused on the development of ALFRED (Advanced Lead-cooled Fast Reactor European Demonstrator) and is supported by the FALCON (Fostering ALfred CONstruction) international consortium. The goal is to construct a technology demonstrator which is also prototypic for a lead-cooled-based small modular reactor. To reach this ambitious goal, an important research, development and qualification infrastructure is planned in Romania, leveraging on the know-how cumulated within European and nationally funded endeavors. In particular, the infrastructure will support the scientific program with experimental campaigns dedicated to bridging the technological and scientific gaps, as well as to support the design and licensing of the reactor. This paper presents the configuration of the ALFRED reactor coolant system showing its present state of development and technological innovations. The current plant architecture provides for a thermal power up to 300 MWth and a coolant temperature range from a minimum of 390 °C to a maximum of 520 °C
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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