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MHD (MAGNETO-HYDRODYNAMICS) IN LIQUID METALS IN FUSION REACTORS: EFFECTS ON TRITIUM TRANSPORT AND INVENTORY
No full textThe Water Cooled Lithium Lead (WCLL) is one of the breeding blanket concepts proposed for DEMO reactor. The velocity field of the electrically conducting lead-lithium eutectic alloy inside the blanket is highly influenced by the external magnetic field used for plasma confinement, due to a magnetohydrodynamic (MHD) effect. In addition, strong temperature gradients give rise to buoyancy forces, that have a great impact on flow behavior. MHD and
convection significantly influences the resulting temperature and velocity fields, and therefore tritium transport. A multi-physics approach of a 3D tritium transport model is presented for a simplified geometry of the WCLL breeding blanket. In particular, MHD, buoyancy forces, advection-diffusion of tritium into the lead-lithium eutectic alloy, transfer of tritium from the liquid interface towards the steel and diffusion of tritium inside the steel have been included in this study. Tritium permeation from PbLi to the baffle, tritium concentrations and inventories inside the lead-lithium and in the EUROFER baffle have been evaluated
TRITIUM IN NUCLEAR FUSION SYSTEMS
No full textTritium, the radioactive isotope of hydrogen, is of main interest in the research and development of fusion technology. In order to establish fusion as an energy source, tritium safety and availability must be achieved. In effect, tritium constitutes a hazard, even in low quantities, and must be handled limiting the releases to the environment. Tritium will be burn in large quantities in the event of nuclear fusion power plants, and being practically non-existent in nature, must be produced by the reactor itself. After a description of tritium radiological characteristics and hazard, the tritium breeding issue is presented, focusing particularly on the most recent European breeding blanket designs
Analysis of MHD and tritium transport in liquid breeders for fusion applications
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Magneto-convective effect on tritium transport at breeder unit level for the WCLL breeding blanket of DEMO
Full text linkThe Water-Cooled Lithium-Lead (WCLL) is one of the four breeding blanket concepts proposed by Europe in view of its DEMO reactor. The velocity field of the electrically conducting lead-lithium eutectic alloy inside the blanket is strongly influenced by the external magnetic field used for plasma confinement combined with buoyancy effect. The strength of the magnetohydrodynamics (MHD) effect and of the magneto-convective effect (MHD and buoyancy force) depends on the intensity of the magnetic field and its orientation with respect to the direction of the lead-lithium motion. This phenomenon significantly influences the resulting temperature and velocity fields, and therefore the tritium transport inside the breeding blanket. A multi-physics approach of a 3D tritium transport model is presented for a simplified geometry of the WCLL breeding blanket. In particular, advection-diffusion of tritium into the lead-lithium eutectic alloy, transfer of tritium from the liquid interface towards the steel, diffusion of tritium inside the steel, transfer of tritium from the steel towards the coolant, and advection-diffusion of diatomic tritium into the coolant, temperature field, velocity fields of both lead-lithium and water, buoyancy forces, and MHD effect have been included in this study. The tritium concentrations and the inventories inside the lead-lithium, in the Eurofer pipes and in the baffle, and in the water coolant have been evaluated
HyPer-QuarCh II: a laboratory-scale device for hydrogen isotopes permeation experiments
Full text linkIn a D-T fusion reactor, the correct estimation of the tritium inventory and permeation fluxes towards the coolant and to the external environment is a crucial issue for the reactor licensing. Within this frame, a fast and reliable sensor for the online measurement of hydrogen isotopes concentration in the breeder is therefore necessary. At ENEA Brasimone research centre, Italy, the development, qualification and characterization of hydrogen isotopes permeation sensors (HPS) were carried out since the early 2000s. A new experimental laboratory-scale device, named Hyper-Quarch II (Hydrogen Permeation Quartz Chamber), was developed on the basis of the experience gained in the past experimental campaigns. This device is characterised by an upgraded test section in quartz and new instrumentation equipment, and will be used to test advanced hydrogen permeation sensor in both gas phase and in stagnant LiPb eutectic alloy (15.7 at.% Li). Hydrogen or deuterium will be adopted instead of tritium to simulate the operative conditions of the Water-Cooled Lithium-Lead (WCLL) Test Blanket Module of ITER and the WCLL Breeding Blanket of the European DEMO reactor. Moreover, the upgrade was performed to also allow the measurement of the Sieverts’ constant of hydrogen or deuterium solubilised in the LiPb with absorption or desorption techniques in a temperature range from 300 to 550∘C and pressure range 0.1 to 100 hPa
Verification and Validation of COMSOL Magnetohydrodynamic Models for Liquid Metal Breeding Blankets Technologies
Full text linkLiquid metal breeding blankets are extensively studied in nuclear fusion. In the main proposed systems, the Water Cooled Lithium Lead (WCLL) and the Dual Coolant Lithium Lead (DCLL), the liquid metal flows under an intense transverse magnetic field, for which a magnetohydrodynamic (MHD) effect is produced. The result is the alteration of all the flow features and the increase in the pressure drops. Although the latter issue can be evaluated with system models, 3D MHD codes are of extreme importance both in the design phase and for safety analyses. To test the reliability of COMSOL Multiphysics for the development of MHD models, a method for verification and validation of magnetohydrodynamic codes is followed. The benchmark problems solved regard steady state, fully developed flows in rectangular ducts, non-isothermal flows, flow in a spatially varying transverse magnetic field and two different unsteady turbulent problems, quasi-two-dimensional MHD turbulent flow and 3D turbulent MHD flow entering a magnetic obstacle. The computed results show good agreement with the reference solutions for all the addressed problems, suggesting that COMSOL can be used as software to study liquid metal MHD problems under the flow regimes typical of fusion power reactors
TRIEX-II: An experimental facility for the characterization of the Tritium Extraction Unit of the WCLL blanket of ITER and DEMO fusion reactors
Full text linkThe experimental qualification of the Tritium Extraction Unit (TEU) from the LiPb eutectic alloy (15.7 at. % Li), the breeder material of the Water-Cooled Lithium-Lead (WCLL) breeding blanket concept, is one of the fundamental items for the demonstration of tritium balance sustainability for ITER and DEMO fusion reactors. Several technologies have been proposed as TEU, but the selection of the reference technology can be carried out only after the experimental measurement of the tritium extraction efficiency. For this purpose, a dedicated facility, called TRIEX-II, was designed and installed at ENEA Brasimone research centre, Italy. The facility is able to qualify Gas-Liquid Contactor (GLC), Permeator Against Vacuum (PAV) and Liquid-Vacuum Contactor (LVC) technologies at different temperatures, lithium-lead mass flow rates and hydrogen isotopes concentrations. In TRIEX-II, the hydrogen or deuterium, used to simulate tritium, are solubilised inside the LiPb with a dedicated saturator and are then extracted from the liquid metal in the GLC mock-up, which uses pure helium or a mixture constituted by helium and hydrogen as stripping gas and works in the temperature range between 300 and 500 °C
A novel approach to the study of magnetohydrodynamic effect on tritium transport in WCLL breeding blanket of DEMO
Full text linkThe Water-Cooled Lithium Lead (WCLL) breeding blanket is one of the European blanket designs proposed for DEMO reactor. Tritium can permeate into the different structural materials, arising potential issues concerning the fuel self-sufficiency and can be lost into the environment with consequent radiological hazard for the population. Within this frame, a tritium transport analysis is fundamental to evaluate tritium retention in LiPb (15.7 at. % Li) and in the structures and tritium permeation fluxes into the cooling water. To assess this study, a portion of the breeder unit of the outboard equatorial module of the WCLL was modelled. The buoyancy forces and the magnetohydrodynamic (MHD) effect were also included. The final system of partial differential equations was solved with a novel approach through COMSOL Multiphysics. The coupled MHD and heat transfer system of equations was solved performing a transient simulation, that was stopped when the main average variables, temperature and velocity, reached a stable condition. In this way, it was possible to determine the lithium-lead velocity field and to use it as an input for the transport analysis. Tritium transport was modelled by using the input data of tritium generation rate and volumetric power deposition coming from an ad-hoc Monte Carlo simulation realized with MCNP software. Moreover, the transport analysis included advection-diffusion of tritium into the LiPb, transfer of tritium from the liquid interface towards the steel, diffusion of tritium inside the steel, transfer of tritium from the steel towards the coolant, advection-diffusion of diatomic tritium into the coolant
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
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