1,720,980 research outputs found
Assessment of size aspects in modelling molten fuel coolant interaction.
Full text linkSevere accidents in light water nuclear reactors occur when reactor vessel water inventory decreases and there is no available additional water coolant to be delivered into the core. In general, during an extended severe accident sequence a period exists in which the reactor core, after a partial or total melt down, is poured into the lower plenum that can have some water present. The study of the interaction of the melt fuel with the water is the objective of MFCI (Melt Fuel Coolant Interaction) activities.MFCI is one of the most important issues awaiting resolution in water cooled reactor safety analysis. The progression of a severe accident in a water cooled reactor can lead to energetic (steam explosion) or non-energetic (melt quenching) interactions as the molten fuel relocates and eventually interacts with the coolant either in the vessel lower head (in vessel) or in the cavity (ex-vessel).The MFCI experiments at JRC Ispra site were conducted in the FARO (Furnace And Release Oven) test facility under realistic melt composition and prototypical accident conditions to provide basic information on underlying phenomena. The experimental programme was complemented by comprehensive pre-test and post-test analytical activities based on the development and application of the thermalhydraulic COMETA (COre MElt Thermalhydraulic Analysis) code. The code is developed and assessed on the basis of experimental information acquired in the FARO facility tests, and there are some limitations and uncertainties in their application to the full plant, which need to be identified and possibly quantified.In general the main objective of the PhD research was achieved expanding the general knowledge in Melt Fuel Coolant Interaction. The knowledge was complemented collaborating and complementing the application of COMETA code under conditions not experimented before, developing and improving COMETA code sources and verifying the code consistency, analysing and unifying the COMETA simulations carried so far.Also a further analytical study was carried out in order to illustrate the MFCI inside the general overview of a NPP (Nuclear Power Plant) severe accident sequence.DOCTORAT EN ENGINYERIA NUCLEAR (Pla 1998
Modelling Molten Fuel Coolant Interaction - Assessment of Size Aspects in Modelling Molten Fuel Coolant Interaction
No full textSevere accidents (SA) in LWR occur when reactor vessel water decreases and there is no available water for cooling the core. During a SA the reactor core could, after partial/total melt down, pour into the lower plenum. The study of the interaction of the melt fuel with the water is the objective of MFCI (Melt Fuel Coolant Interaction) activities. MFCI is an important issue in reactor safety analysis. The SA can lead to energetic (steam explosion) or non-energetic (melt quenching) interactions in-vessel or ex-vessel. FARO facility at JRC-Ispra simulated MFCI experiments under real conditions. Pre-test/post-test analytical activities using the TH COMETA code were carried out. The code was assessed based on FARO tests. Limitations and uncertainties in the application to a full plant needed to be identified and quantified. The research objective was achieved expanding the knowledge in MFCI. It was complemented with application of COMETA to conditions not experimented before, developing and improving COMETA sources and verifying code consistency, analysing and unifying the COMETA simulations. An analytical study was carried out to illustrate the MFCI inside a NPP SA sequence.JRC.F.5 - Safety of present nuclear reactor
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
The Stresa database: A token for the future
No full textThe experimental data recorded in Integral Effect Test Facilities (ITFs) are traditionally used in order to validate Best Estimate (BE) system codes and to investigate the behaviour of Nuclear Power Plants (NPP) under accident scenarios. In the same way, facilities dedicated to specific thermal-hydraulic Severe Accident (SA) phenomena are used for the development and improvement of specific analytical models and codes used in the SA analysis for Light Water Reactors (LWR).
The Joint Research Centre (JRC), Ispra site, of the European Commission (EC) carried out important projects since the 70’s for the production of reactor safety experimental data. The LOBI was a reactor thermalhydraulic safety research programme (1970-1994) that produced a lot of ITF experimental data for a range of PWR operational and accident conditions. In the area of SA, the FARO, KROTOS facilities (1991-2000) simulated Melt Fuel Coolant Interaction (MFCI) phenomena, considering either in-vessel (quenching) and ex-vessel (spreading) experiments and potential situations for steam explosions. The STORM facility simulated experiments in the area of Aerosol Transport.
Experimental data mentioned above were stored in the STRESA (Storage of Thermal REactor Safety Analysis Data) database developed by the JRC Ispra site. At present the JRC STRESA database is hosted and maintained by JRC Petten site.
The paper presents these past activities on the production of experimental data and its storage in the JRC STRESA database in order to further disseminate, promote the usage of the database containing these data and to demonstrate long-term importance of well maintained experimental databases.JRC.F.5 - Nuclear Reactor Safety Assessmen
Validation of ASTEC v2.0 corium jet fragmentation model using FARO experiments
No full textASTEC is an integral code for the prediction of Severe Accidents in Nuclear Power Plants. As such, it needs to cover all physical processes that could occur during accident progression, yet keeping its models simple enough for the ensemble to stay manageable and produce results within an acceptable time.
The present paper is concerned with the validation of the Corium jet fragmentation model of ASTEC v2.0 rev3 by means of a selection of six experiments carried out within the FARO facility. The different conditions applied within these six experiments help to analyse the model behaviour in different situations and to expose model limits. In addition to comparing model outputs with experimental measurements, sensitivity analyses are applied to investigate the model.
Results of the paper are (i) validation runs, accompanied by an identification of situations where the implemented fragmentation model does not match the experiments well, and discussion of results; (ii) its special attention to the models calculating the diameter of fragmented particles, the identification of a fault in one model implemented, and the discussion of simplification and ad hoc modification to improve the model fit; and, (iii) an investigation of the sensitivity of predictions towards inputs and parameters.
In this way, the paper offers a thorough investigation of the merit and limitation of the fragmentation model used in ASTEC.JRC.F.5 - Nuclear Reactor Safety Assessmen
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