1,720,973 research outputs found
A short overview of ITER-like pulsed MCF reactors application as hybrid nuclear systems for actinides transmutation
No full textThe fusion-fission hybrid reactor is a promising technology that is likely to assume more and more importance in the
global energy scenario in the coming years. Although this kind of nuclear system dates back to the earliest times of the
fusion projects (when it was recognized that using fusion neutrons to “support” nuclear fission fuel cycle could widely
increase the exploitation of the fusion plants), it appears to receive relatively limited attention since the mid-1980s.
Notwithstanding, hybrid fusion fission systems have been already studied for some decades, in the most prominent
laboratories and a relatively large bibliography was produced. Obviously much more papers on this topic have been
published in more recent years.
The fusion-fission hybrid concept can use both the nuclear fusion and fission processes: in a typical application, neutrons
from fusion reactions can be used to sustain the fission chain of a sub-critical system. This is the basis of the hybrid
reactor concept: neutron generation is not produced just in neutron-induced fissions, but also as a “by-product” of the
fusion reactions inside the nuclear fusion reactor “core” (i.e., respectively, the void chamber for MCF or the fuel particles
for ICF). This method allows to have an intrinsically safe facility (with a higher efficiency than a fusion reactor itself and
a harder neutron energy spectrum than a fission reactor) which could be suitable for nuclear waste transmutation, too.
In the last years, many initiatives on nuclear waste transmutation were proposed in order to reduce the long-term
radiotoxicity of the wastes by eliminating a high fraction of the TRU from the SNF before their final disposal. In this
frame, as already anticipated, hybrid fusion-fission systems could have an additional degree of freedom because of the
independent source: this means that the neutron spectrum can be (reasonably) tailored for the transmutation purposes.
In the present study a special focus has been devoted to the transmutation of SNF from fission reactors loaded in a
fusion system, operated under the hypothesis to take into account the behaviour of a planned “real” (i.e. pulsed) MCF
(ITER-like) plant
Design by theoretical and CFD analyses of a multi-blade screw pump evolving liquid lead for a Generation IV LFR
No full textLead-cooled fast reactor (LFR) has both a long history and a penchant of innovation. With early work related to its use for submarine propulsion dating to the 1950s, Russian scientists pioneered the development of reactors cooled by heavy liquid metals (HLM). More recently, there has been substantial interest in both critical and subcritical reactors cooled by lead (Pb) or Lead-Bismuth eutectic (LBE), not only in Russia, but also in Europe, Asia, and the USA. The growing knowledge of the thermal-fluid-dynamic properties of these fluids and the choice of the LFR as one of the six reactor types selected by Generation IV International Forum (GIF) for further research and development has fostered the exploration of new geometries and new concepts aimed at optimizing the key components that will be adopted in the Advanced Lead Fast Reactor European Demonstrator (ALFRED), the 300 MWth pool-type reactor aimed at proving the feasibility of the design concept adopted for the European Lead-cooled Fast Reactor (ELFR). In this paper, a theoretical and computational analysis is presented of a multi-blade screw pump evolving liquid Lead as primary pump for the adopted reference conceptual design of ALFRED. The pump is at first analyzed at design operating conditions from the theoretical point of view to determine the optimal geometry according to the velocity triangles and then modeled with a 3D CFD code (ANSYS CFX). The choice of a 3D simulation is dictated by the need to perform a detailed spatial simulation taking into account the peculiar geometry of the pump as well as the boundary layers and turbulence effects of the flow, which are typically tri-dimensional. The use of liquid Lead impacts significantly the fluid dynamic design of the pump because of the key requirement to avoid any erosion affects. These effects have a major impact on the performance, reliability and lifespan of the pump. Albeit some erosion-related issues remain to be fully addressed, the results of this analysis show that a multi-blade screw pump could be a viable option for ALFRED from a thermo-fluid-dynamic point of view
THEORETICAL AND NUMERICAL INVESTIGATION OF THREE DESIGNS FOR A PRIMARY CIRCULATION PUMP EVOLVING LIQUID LEAD FOR GEN-IV REACTORS
No full textNumerical investigation on a jet pump evolving liquid lead for GEN-IV reactors
No full textHeavy-liquid metals, such as lead and lead–bismuth eutectic, are promising candidates as coolant for advanced GEN-IV fast reactors as well as for Accelerator-Driven Systems. The advancing knowledge of the thermal-hydraulic behavior of these fluids leads to explore new geometries and new concepts aimed at optimizing the key components of a GEN-IV reactor for these fluids. In this paper, a theoretical and computational analysis is presented of a jet pump evolving liquid lead as primary pump for ALFRED (Advanced Lead Fast Reactor European Demonstrator). The jet pump is modeled with a 3D CFD code (FLUENT) and at design operating conditions. The analysis shows that a jet pump could be a viable solution for ALFRED (at least from a thermal-hydraulic point of view), albeit some technological issues remain to be fully addressed
Theory, design and CFD analysis of a multi-blade screw pump evolving liquid lead for a GEN-IV LFR Nuclear Power Plant
No full textIn this presentation, a theoretical and computational analysis is presented of a multi-blade screw pump evolving liquid Lead as primary pump for the reference conceptual design of the Advanced Lead Fast Reactor European Demonstrator (ALFRED).
The pump is analyzed at design operating conditions from the theoretical point of view to determine the optimal geometry according to the velocity triangles and then modeled with the 3D CFD code ANSYS CFX.
The choice of a 3D simulation is dictated by the need to perform a detailed spatial simulation taking into account the peculiar geometry of the pump as well as the boundary layers and turbulence effects of the flow, which are typically tri-dimensional. The use of liquid Lead impacts significantly the fluid dynamic design of the pump because of the key requirement to avoid any velocity-related erosion phenomenon. Albeit some erosion-related issues remain to be fully addressed, the results of this 3D analysis show that a multi-blade screw pump could be a viable option for ALFRED from a thermo-fluid-dynamic point of view
Numerical investigation of turbulent flow within a channel with chamfered edge ribs in stream-wise direction
No full textThe present paper reports a numerical investigation of a forced convection water flow within a two-dimensional ribbed channel. A uniform heat flux is applied on the external walls. The flow regime is turbulent and Reynolds numbers are in the range 10·10^3÷100·10^3. Square and chamfered rib shapes with different arrangements are analyzed in terms of various dimensionless heights and pitches of elements. The investigation is accomplished by using a CFD code and its aim consists in finding of arrangements to obtain a high Performance Evaluation Criterion (PEC). Results are presented in terms of temperature and velocity fields, profiles of average Nusselt number, average heat transfer coefficients and required pumping power. Heat transfer enhancement increases with the ribs presence, but it is accompanied by an increasing pumping power. In particular, the best performances in terms of Nusselt are shown for p/e = 4 and 12 for both the square and chamfered cases. The heat transfer improves as Reynolds number raises, but a substantial increase of pumping power is also observed. The utilization of chamfered ribs allows to increase the PEC, especially at low Re. The maximum PEC is equal to 1.3 and it is obtained for Re = 10^4 and p/e = 4
CFD initial assessment of a protrusions based experimental facility
No full textThe design of compact heat exchangers and their mass flow distributors is still based on empirical approaches and both experimentations and numerical analyses are needed for defining the best geometries able to reduce the mass flow rate non uniformities in parallel channels. This is a cause of reduction in both thermal and fluid-dynamic performances.
In this paper, a series of single-phase and two-phase CFD simulations on water and water with air injection are carried out in order to estimate the capabilities of the solvers implemented in the OpenFOAM code to reproduce (in comparison with experimental data) such kind of configurations and phenomena. The effects of different turbulence models implemented in OpenFOAM are investigated; additionally, some general considerations on the differences and analogies among different Reynolds numbers flow and turbulence model effects applied to the present configuration are discussed. Finally, by the point of view of two-phase flow, the capability of the code to reproduce the intermittent behaviour is investigated, with the aim of obtaining an acceptable simulation of the non-uniform mass flow distribution in each protrusion; the obtained results are also compared with both ANSYS-FLUENT and STARCCM+ commercial codes
CFD preliminary assessment of a protrusions based facility
No full textThe design of compact heat exchangers and their mass flow distributors is still based on empirical approaches and both numerical analyses and experimentations are needed for designing the best geometries useful to reduce the mass flow rate non uniformities in parallel channels. As known, this is indeed a cause of reduction in both thermal and fluid-dynamic performances. In this paper a series of single-phase CFD simulations on water and water with air injection are carried out in order to estimate the capabilities of the solvers implemented in the OpenFOAM code to reproduce (in comparison with experimental data) such kind of configurations and phenomena. The effects of different turbulence models (both RANS and LES) implemented in OpenFOAM are investigated; additionally some general considerations on the differences and analogies among different Reynolds numbers flow and turbulence model effects applied to the present configuration are discussed. Finally, the capability of the code to reproduce the peculiar behaviour of a protrusions based experimental facility is investigated, with the aim of obtaining an acceptable simulation of the non-uniform mass flow distribution in each protrusion. The present paper is an extended version including the main conclusions and observations emerged in the 2nd AIGE-IIETA International Conference in Genoa
Assessment of a 2D CFD model for a single phase natural circulation loop
No full textThe use of passive safety systems are more and more diffused in many technological fields. Natural circulation is probably one of the main phenomenon applied in this kind of systems: indeed, as known, by means of gravity and buoyancy forces, the fluids can circulate without any external power sources. In this paper a preliminary analysis (also by comparisons between experimental tests and numerical simulations) of a natural circulation based loop (namely a natural circulation based facility installed at University of Genova) is presented. Starting from some experimental results, the data deriving from CFD loop simulations (both in steady and in unsteady conditions) are used for a first preliminary validation, mainly in order to have a computational tool reliable and able to computationally simulate motion inversions related phenomena. The physical inversions phenomena are very well reproduced also by the a simplified numerical 2D model of the loop, and the physical considerations related to the temperature and velocity fluctuations during the transient simulations, are in agreement with the well-known observations formulated by Welander on the basis of a simple point source analysis scheme
Application of Serpent 2 and MCNP6 to study different criticality configurations of a VVER-1000 mock-up
No full textThis paper shows some results obtained through simulating a VVER-1000 mock-up installed within the LR-0 research reactor in the Research Centre Řež (Czech Republic): the simulations have been performed by using the Serpent 2 and MCNP6 Monte Carlo codes. The mock-up is analysed in 6 different critical configurations, obtained with variation of coolant level and boron concentration. Some important nuclear parameters are evaluated in different positions of the mock-up, in order to know how the level of coolant influences the flux, the fission density, the reaction rate and the neutron spectrum changes, although the reactor remains with keff around 1.0 to less than 300 pcm of reactivity
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