1,721,022 research outputs found
Application of CFX-10 to the investigation of RPV coolant mixing in VVER reactors
No full textCoolant mixing phenomena occurring in the pressure vessel of a nuclear reactor constitute one of the main objectives of investigation by researchers concerned with nuclear reactor safety. For instance, mixing plays a relevant role in reactivity-
induced accidents initiated by deboration or boron dilution events, followed by transport of a deborated slug into the vessel of a pressurized water reactor. Another example is constituted
by temperature mixing, which may sensitively affect the
consequences of a pressurized thermal shock scenario.
Predictive analysis of mixing phenomena is strongly improved
by the availability of computational tools able to cope with the inherent three-dimensionality of such problem, like system
codes with three-dimensional capabilities, and Computational Fluid Dynamics (CFD) codes. The present paper deals with numerical analyses of coolant mixing in the reactor pressure
vessel of a VVER-1000 reactor, performed by the ANSYS CFX-10 CFD code. In particular, the “swirl” effect that has been observed to take place in the downcomer of such kind of
reactor has been addressed, with the aim of assessing the
capability of the codes to predict that effect, and to understand the reasons for its occurrence. Results have been compared against experimental data from V1000CT-2 Benchmark.
Moreover, a boron mixing problem has been investigated, in the
hypothesis that a deborated slug, transported by natural
circulation, enters the vessel. Sensitivity analyses have been conducted on some geometrical features, model parameters and boundary conditions
CFD Code Validation and Benchmarking Against Stratified Air-Water Flow Experimental Data
No full textPressurized thermal shock (PTS) modelling has been identified as one of the most important industrial needs related to nuclear
reactor safety. A severe PTS scenario limiting the reactor pressure vessel (RPV) lifetime is the cold water emergency core cooling
(ECC) injection into the cold leg during a loss of coolant accident (LOCA). Since it represents a big challenge for numerical
simulations, this scenario was selected within the European Platform for Nuclear Reactor Simulations (NURESIM) Integrated
Project as a reference two-phase problem for computational fluid dynamics (CFDs) code validation. This paper presents a CFD
analysis of a stratified air-water flow experimental investigation performed at the Institut de M ́ecanique des Fluides de Toulouse
in 1985, which shares some common physical features with the ECC injection in PWR cold leg. Numerical simulations have
been carried out with two commercial codes (Fluent and Ansys CFX), and a research code (NEPTUNE CFD). The aim of this
work, carried out at the University of Pisa within the NURESIM IP, is to validate the free surface flow model implemented in
the codes against experimental data, and to perform code-to-code benchmarking. Obtained results suggest the relevance of threedimensional
effects and stress the importance of a suitable interface drag modelling
CFX-10 and Relap5-3D Simulations of Coolant Mixing Phenomena in RPV of VVER-1000 Reactors
No full textThe present paper deals with numerical analyses of coolant mixing in the reactor
pressure vessel of a VVER-1000 reactor, performed with the ANSYS CFX-10 CFD code and
with the RELAP5-3D system code. In particular, the attention focused on the “swirl” effect
that has been observed to take place in the downcomer of such kind of reactor, with the aim of
assessing the capability of the codes to predict that effect, and to understand the reasons for its
occurrence. The results have been compared against experimental data from V1000CT-2
Benchmark
CFD Code Validation against Stratified Air-Water Flow Experimental Data
No full textPressurized Thermal Shock (PTS) modelling has been identified as one of the most
important industrial needs related to nuclear reactor safety. A severe PTS scenario limiting the Reactor Pressure Vessel (RPV) lifetime is the cold water Emergency Core Cooling (ECC)
injection into the cold leg during a Loss of Coolant Accident (LOCA). Since it represents a big challenge for numerical simulations, this scenario was selected within the NURESIM
(European Platform for Nuclear Reactor Simulations) Integrated Project as a reference two-
phase problem for CFD code validation. This paper presents a CFD analysis of a stratified air-water flow experimental investigation performed at the Institut de Mécanique des Fluides de
Toulouse in 1985 [1], which shares some common physical features with the ECC injection in PWR cold leg. Numerical simulations have been carried out with two commercial codes (Fluent and Ansys CFX), and a research code NEPTUNE_CFD (developed by EDF and CEA). The aim of this work, carried out at the University of Pisa within the NURESIM IP, is to validate the free surface flow model implemented in the codes against the available
experimental data, and to perform code to code benchmarking. Obtained results suggest the
relevance of three-dimensional effects and stress the importance of a suitable interface drag
coefficient modelling. A relevant improvement of results has been achieved with 3D simulations, even if the air velocity profile was still significantly underestimated
Instrumenting Full scale Boron Injection Test Facility to support Atucha-2 NPP licensing
Full text linkThe Atucha-2 Pressurized Heavy Water Reactor is equipped with a back-up shutdown system based
on the fast injection of boron into the moderator tank. Such system had initially been designed to
cope with a 10%-area (0.1A) break Loss Of Coolant Accident (LOCA) scenario, but based on upgraded
licensing requirements the design had to be revised and possibly improved against a double-ended
guillotine (2A) break LOCA. In particular, the boron injection had to be proven fast enough to allow a
timely shutdown of the reactor, even in the case of a failure of the primary shutdown system
(control rods).
A full-scale test facility was built for such “design validation” purpose, in the framework of a
cooperation program between the University of Pisa – San Piero a Grado Nuclear Research Group
(GRNSPG) and the utility Nucleoeléctrica Argentina S.A. (NA-SA). A special instrumentation system,
based on conductivity probes designed on purpose by the Helmholtz Zentrum Dresden-Rossendorf
(HZDR), was adopted for the measurement of the injection delay, as well as for the monitoring of
pressure at several key locations. Care was taken to reproduce the relevant NPP conditions as closely
as possible to those expected on the basis of extensive safety analyses performed adopting a Best
Estimate Plus Uncertainty (BEPU) approach. In this respect, not only the test facility is full-scale, but
also the key components (such as the fast opening air valves, the boric acid tanks, the rupture
device, the injection lance) were directly borrowed from the Atucha-2 NPP.
The experimental campaign carried out by NA-SA on such test facility allowed to improve the design
of the boron injection system (especially as to some fluid-structure interaction issues) and finally to
achieve the main goal, i.e. the demonstration that the system’s performance is fast enough to assure
a timely and safe shutdown of the reactor. This was a key contribution to the successful completion
of the NPP licensing process
Verifica e validazione preliminare sull'accoppiamento del codice di calcolo RELAP5-3D e il codice di fluidodinamica computazionale ANSYS CFX
Full text linkThis report describes the work performed by the Gruppo di Ricerca Nucleare di San Piero a Grado (GRNSPG) of the University of Pisa (member of CIRTEN consortium) in the frame of the “Accordo di Programma MSE-ENEA sulla Ricerca di Sistema Elettrico - Piano Annuale di Realizzazione 2014”, particularly Project B.3.1, Task LP2.c.1_e. Aim of the work was to further improve and qualify a software interface that allows performing CFD-system code simulations, which had been developed by the same working group during previous PARs. Namely, the coupling tool was parallelized, so as to dramatically improve the cost-effectiveness of the coupled simulations compared to “serial” runs, and further Verification and Validation work was carried out by the simulation of experimental tests dealing with natural and assisted circulation of liquid metals in closed loops
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
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