Papers by Walter Borreani
A short overview of ITER-like pulsed MCF reactors application as hybrid nuclear systems for actinides transmutation
The fusion-fission hybrid reactor is a promising technology that is likely to assume more and mor... more The 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 \u201csupport\u201d 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 reac...
Theoretical and Numerical Investigation of Three Designs for a Primary Circulation Pump Evolving Liquid Lead for Gen-IV Reactors
A new hybrid fast-slow ADS for research and applications
Third International Workshop on Technology and Components of Accelerator-Driven Systems (TCADS-3), 2017
We report on the studies of an irradiation facility based on an accelerator-driven subcritical nu... more We report on the studies of an irradiation facility based on an accelerator-driven subcritical nuclear research reactor, which can simultaneously provide a fast flux in the core and a thermal flux in the reflector, that we will call a hybrid fast-slow ADS. The conceptual design presented here, inspired by [1], starts from a 432 kW (keff=0.967) ADS composed by 110 solid lead fuel assemblies each with size 9.7 x 9.7 x 87 cm3, filled with 81 MOX pins (16.5% Pu+Am) of 0.357 cm radius and surrounded by a 0.068 cm thick AISI steel cladding. Source neutrons are produced by a 70 MeV 1 mA proton beam impinging on a beryllium target (~ 8 x 1014 n/sec) [2].The core is cooled by helium flowing in very thin pipes, 0.25 cm in diameter and is surrounded by a 80 cm lead reflector. Core and reflector are contained within a 2 cm steel vessel. The hybrid version (keff 0.972= P=527 kW) is instead composed by 59 fuel assemblies, each hosting 81 MOX pins (22% Pu+Am) where: - The lead reflector has been replaced by three concentric layers, the first of 35 cm lead, followed by 50 cm graphite and finally 10 cm lead. - In the cooling system water flows in wider pipes, 0.5 cm in diameter, which allows to increase keff while maintaining the fast character of the spectrum. We simulated the neutron flux in three core positions (internal, intermediate and external) and in two graphite reflector positions (internal, intermediate), finding that the flux is still mostly fast in the core, while it exhibits a strong thermal component in the reflector, as shown in the following table. This work is partially supported by the 7th Framework Programmes of the European Commission (Euratom) through the CHANDA contract FP7-Fission-2013-605203
Heavy Liquid Metals (HLM) are objects of interest in the nuclear research sector because of their... more Heavy Liquid Metals (HLM) are objects of interest in the nuclear research sector because of their optimal thermal and neutronic properties; the development and the validation of models allowing to predict their behaviour are fundamental for the future development of the Generation IV energy systems. An experimental facility named SESAME-stand, is planned to be operated at Research Centre Rez (RC-Rez) under the framework of SESAME project. The aim of the facility is to study the solidification of Lead under GEN-IV Heavy Liquid Metal pool type nuclear reactors relevant conditions and to provide a database for the benchmarking and validation of
Energies, 2018
Accelerator Driven Systems (ADS) seem to be a good solution for safe nuclear waste transmutation.... more Accelerator Driven Systems (ADS) seem to be a good solution for safe nuclear waste transmutation. One of the most important challenges for this kind of machine is the target design, particularly for what concerning the target cooling system. In order to optimize this component a CFD-based approach has been chosen. After the definition of a reference design (Be target cooled by He), some parameters have been varied in order to optimize the thermal-fluid-dynamic features. The final optimized target design has an increased security margin for what regarding Be melting and reduces the maximum coolant velocity (and consequently even more the pressure drops).
Energies, 2017
Although Lead-cooled Fast Reactor (LFR) is not a new concept, it continues to be an example of in... more Although Lead-cooled Fast Reactor (LFR) is not a new concept, it continues to be an example of innovation in the nuclear field. Recently, there has been strong interest in liquid lead (Pb) or liquid lead-bismuth eutectic (LBE) both critical and subcritical systems in a relevant number of Countries, including studies performed in the frame of GENERATION-IV initiative. In this paper, the theoretical and computational findings for three different designs of Primary Circulation Pump (PCP) evolving liquid lead (namely the jet pump, the Archimedean pump and the blade pump) are presented with reference to the ALFRED (Advanced Lead Fast Reactor European Demonstrator) design. The pumps are first analyzed from the theoretical point of view and then modeled with a 3D CFD code. Required design performance of the pumps are approximatively around an effective head of 2 bar with a mass flow rate of 5000 kg/s. Taking into account the geometrical constraints of the reactor and the fluid dynamics characteristics of the molten lead, the maximum design velocity for molten lead fluid flow of 2 m/s may be exceeded giving rise to unacceptable erosion phenomena of the blade or rotating component of the primary pumping system. For this reason a deep investigation of non-conventional axial pumps has been performed. The results presented shows that the design of the jet pump looks like beyond the current technological feasibility while, once the mechanical challenges of the Archimedean (screw) pump and the fluid-dynamic issues of the blade pump will be addressed, both could represent viable solutions as PCP for ALFRED. Particularly, the blade pump shows the best performance in terms of pressure head generated in normal operation conditions as well as pressure drop in locked rotor conditions. Further optimizations (mainly for what the geometrical configuration is concerned) are still necessary.
Thermal Science and Engineering Progress, 2018
The design of compact heat exchangers and their mass flow distributors is still based on empirica... more The 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.
Thermal Science and Engineering Progress, 2018
The European Physical Journal Plus, 2019
Science and Technology of Nuclear Installations, 2017
The CFD analysis of a Venturi nozzle operating in LBE (key component of the CIRCE facility, owned... more The CFD analysis of a Venturi nozzle operating in LBE (key component of the CIRCE facility, owned by ENEA) is presented in this paper. CIRCE is a facility developed to investigate in detail the fluid-dynamic behavior of ADS and/or LFR reactor plants. The initial CFD simulations have been developed hand in hand with the comparison with experimental data: the test results were used to confirm the reliability of the CFD model, which, in turn, was used to improve the interpretation of the experimental data. The Venturi nozzle is modeled with a 3D CFD code (STAR-CCM+). Later on, the CFD model has been used to assess the performance of the component in conditions different from the ones tested in CIRCE: the performance of the Venturi is presented, in terms of pressure drops, for various operating conditions. Finally, the CFD analysis has been focused on the evaluation of the effects of the injection of an inert gas in the flow of the liquid coolant on the performance of the Venturi nozzle.
International Journal of Heat and Technology, 2017
The use of passive safety systems are more and more diffused in many technological fields. Natura... more The 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.
International Journal of Heat and Technology, 2017
The design of compact heat exchangers and their mass flow distributors is still based on empirica... more The 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 fluiddynamic 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.
International Journal of Heat and Technology, 2017
Aim of this work is the preliminary thermal-fluid-dynamic assessment of a subcritical system to p... more Aim of this work is the preliminary thermal-fluid-dynamic assessment of a subcritical system to perform integral measurements on transmutation processes, designed in the frame of EU CHANDA project: in particular, a low power Accelerator Driven System (ADS) may represent an attractive intermediate step to fill the gap between existing and future facilities like MYRRHA (or possibly EFIT). The activity finds its place within the roadmap for the evaluation of transmutation processes in ADSs, where currently measurements are performed on the zero-power ADS Guinevère at SCK•CEN (Mol, Belgium), while in the future it is expected that MYRRHA will be the major high-power facility for performing this kind of studies and assessing the performance of a fast ADS. The neutronic characterization and burn-up simulations based on Monte Carlo codes of the reactor core allowed the definition of the geometry and the composition of the fuel assembly and, therefore, the thermal power to be removed. On this basis a thermo-fluid-dynamic assessment, through simple analytical accounts and detailed 3D CFD calculations by ANSYS FLUENT v17.0 and OpenFOAM-v1612+, was made.
Numerical investigation of turbulent flow within a channel with chamfered edge ribs in stream-wise direction
Heat and Mass Transfer, 2017
The present paper reports a numerical investigation of a forced convection water flow within a tw... more The 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 10·103÷100·103. 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 = 104 and p/e = 4.
EPJ Web of Conferences, 2017
The neutron multiplication factor k e f f is a key quantity to characterize subcritical neutron m... more The neutron multiplication factor k e f f is a key quantity to characterize subcritical neutron multiplying devices and for understanting their physical behaviour, being related to the fundamental eigenvalue of Boltzmann transport equation. Both the maximum available power-and all quantities related to it, like, e.g. the effectiveness in burning nuclear wastes-as well as reactor kinetics and dynamics depend on k e f f. Nevertheless, k e f f is not directly measurable and its determination results from the solution of an inverse problem: minimizing model dependence of the solution for k e f f then becomes a critical issue, relevant both for practical and theoretical reasons.
CFD Pre-Test Analysis and Design of the NACIE-UP BFPS Fuel Pin Bundle Simulator
Volume 2: Smart Grids, Grid Stability, and Offsite and Emergency Power; Advanced and Next Generation Reactors, Fusion Technology; Safety, Security, and Cyber Security; Codes, Standards, Conformity Assessment, Licensing, and Regulatory Issues, 2016
In the context of GEN-IV heavy liquid metal-cooled reactors safety studies, the flow blockage in ... more In 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 co...
Annals of Nuclear Energy, 2016
This paper shows some results obtained through simulating a VVER-1000 mock-up installed within th... more This paper shows some results obtained through simulating a VVER-1000 mock-up installed within the LR-0 research reactor in the Research Centre Ř ež (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 k eff around 1.0 to less than 300 pcm of reactivity.
Design by theoretical and CFD analyses of a multi-blade screw pump evolving liquid lead for a Generation IV LFR
Nuclear Engineering and Design, 2016
Abstract Lead-cooled fast reactor (LFR) has both a long history and a penchant of innovation. Wit... more Abstract Lead-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 MW t 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.
Preliminary results for the 3D analysis of the flowfield in the lead-cooled steam generator of the ALFRED nuclear reactor with ANSYS/FLUENT
The Generation IV International Forum (GIF) member countries identified the six most promising ad... more The Generation IV International Forum (GIF) member countries identified the six most promising advanced reactor systems and related fuel cycle as well as the research and development necessary to develop these concepts for potential deployment. Among the most promising reactor technologies for fast reactors being considered by the GIF (Sodium and Lead Fast Reactors), the Lead Fast Reactor has been identified as a technology with great potential to meet the needs for both remote sites and central power stations. To enable the design of the industrial-size reactor (code name ELFR, European Lead-cooled Fast Reactor), the design of a low cost but fully representative, scaled-down demonstrator of appropriate size (code-name ALFRED, Advanced Lead Fast Reactor European Demostrator) is performed within the EU-funded LEADER (Lead-cooled European Advanced DEmonstration Reactor) project, started in 2010 and currently under development. The preliminary results of the CFD analysis, performed wit...
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Papers by Walter Borreani