Design Of Liquid Metal Blankets Research Articles

Towards the simulation of MHD flow in an entire WCLL TBM mock-up

In the frame of the EUROfusion breeding blanket research activities, the water cooled lead lithium (WCLL) blanket is considered as reference liquid metal blanket design to be tested in ITER and to be used in a DEMO reactor. For the study of pressure and flow distribution in a WCLL blanket module, magnetohydrodynamic (MHD) phenomena, which result from the motion of the electrically conducting breeder in the intense plasma-confining magnetic field, have to be taken into account. They are due to the induction of electric currents that generate strong electromagnetic forces, which modify the velocity distribution in the blanket compared to hydrodynamic conditions and increase pressure losses. In the WCLL test blanket module (TBM) for ITER a basic geometry, consisting of a rectangular box, representing the breeding zone, is repeated along the poloidal direction. The manifold that distributes and collects the liquid metal features two long poloidal ducts, electrically connected across a common wall. The final goal of the present work is to simulate liquid metal MHD flows in strong magnetic fields in a complete column of a WCLL TBM including poloidal manifolds and 8 breeder units. With this aim, the complexity of the model geometry has been progressively increased and various topologies of computational grids have been considered. First simulations have been performed in a single breeder zone connected with a portion of manifolds in order to test the suitability of the generated grid and the performance of the numerical code for this type of problem. In a second step, the MHD flow at moderate magnetic fields in an entire TBM mock-up has been simulated to get pressure distribution along the manifolds and flow partitioning among breeder units.

Magnetohydrodynamic velocity and pressure drop in manifolds of a WCLL TBM

In the frame of the EUROfusion breeding blanket research activities, the water cooled lead lithium (WCLL) blanket is considered as reference liquid metal blanket design to be tested in ITER and to be used in a DEMO reactor. The design of breeding blankets represents a major challenge for fusion reactor engineering because of the performance requirements and the severe operating conditions in terms of heat load and neutron flux. Liquid metal alloys such as lead-lithium, PbLi, are considered as breeder material, due to their lithium content required for tritium production, and as heat transfer medium because of their large thermal conductivity and the possibility to be operated at high temperature. On the other hand, the motion of the electrically conducting breeder in the plasma-confining magnetic field induces electric currents and generates strong electromagnetic forces that modify significantly the velocity distribution in the blanket compared to hydrodynamic conditions and increase pressure losses. Magnetohydrodynamic (MHD) pressure drops have to be carefully quantified, since excessive values can jeopardize the feasibility of the considered blanket concept. The present work investigates numerically liquid metal MHD flows in manifolds of a WCLL test blanket module. Velocity and pressure distributions are analyzed.

Numerical simulation of liquid metal MHD flows in a conducting rectangular duct with triangular strips

Magnetohydrodynamic (MHD) pressure drop remains a key issue in the application of liquid metal blankets in nuclear fusion reactors. MHD pressure drops and velocity distributions in MHD duct flows are closely related to the shape of the duct cross-section. In this paper, MHD flows in an ordinary electrically conducting rectangular duct (R-duct), and an electrically conducting rectangular duct with triangular strips (RTS-duct) subjected to a uniform magnetic field are investigated numerically using an in-house MHD solver developed in OpenFOAM. The results show that the velocity fluctuation of the MHD flow in the RTS-duct grows, and the dimensionless MHD pressure drop reduces as the direction of the magnetic field is fixed, and the Hartmann number increases. The velocity fluctuation in the RTS-duct spreads more easily when the triangular strips (TS) are on the Hartmann walls instead of the side walls as the magnetic field intensity is the same. Besides, the MHD pressure drop in the RTS-duct is only a little bit higher than that in the R-duct as the TSs are on the Hartmann walls. The MHD pressure drop in the RTS-duct is over 20 % higher than that in the R-duct, and the relative difference increases with the Hartmann number increasing when the TSs are on the side walls. The results about the MHD pressure drop and the flow instability in the RTS-duct can be referenced in the liquid metal blanket design.

Influence of PbLi hydraulic path and integration layout on MHD pressure losses

Abstract A critical point in the design of liquid metal blankets for fusion reactors is the accurate estimate of magnetohydrodynamic (MHD) pressure losses caused by the interaction between flowing breeder and magnetic field. In the Water-Cooled Lithium Lead (WCLL), the liquid metal (PbLi) is used as tritium breeder and carrier, whereas power extraction is delegated to water, thus allowing to minimize the breeder velocity. However, pressure drop for the PbLi loop is expected to remain significant due to high field intensity and direct electrical contact at fluid/wall interface. In this study, a comparative analysis between four alternative WCLL-DEMO configurations is performed to investigate the influence of blanket layout and piping system integration on this variable. Empirical and semi-empirical correlations, supported by numerical simulation results, have been used to estimate the baseline MHD loss, thus neglecting secondary contributions from viscous, inertial, and coupling effects. The larger contribution has been observed in the connection pipes, which are characterized by extensive length, high velocity, and large field gradients. Integration scheme with DEMO reactor is also a key factor, whereas breeding zone and manifold layout play secondary, albeit significant, roles in determining overall MHD loss. Adopting insulating elements in feeding and draining pipes should be carefully considered to reduce PbLi pumping requirements. Further numerical and experimental characterization of 3D MHD flow in manifolds and for coupling phenomena is vigorously suggested to reduce the uncertainty about blanket flow distribution and pressure loss estimate.

Numerical research of magnetohydrodynamics buoyant flow in dual functional lead lithium fusion blanket

Blanket is key component of fusion reactor, which functions as tritium breeder, energy conversion component and radiation shield. Liquid metal fusion blanket is a promising candidate of future fusion power plants for its high temperature operating characteristics and efficient thermoelectric conversion. However, motion of liquid metal under fusion reactor high magnetic field (∼4 T) causes serious magnetohydrodynamics (MHD) effect, and extreme non-uniform volumetric heat deposited by fusion neutrons produces strong buoyancy effect. Both effects greatly change flow field and heat transfer characteristics of liquid metal blanket, which are key issues for thermal-hydraulic design of liquid metal blankets. In this paper, MHD buoyant flow of Dual Functional Lead Lithium blanket (DFLL) under typical fusion magnetic field and non-uniform volumetric nuclear heating were studied. Buoyancy force induced drastic natural convection in LL1 (the 1st Lead Lithium channel) channel of blanket and increased the heat leaked to Helium coolant and reduced the outlet temperature. FCI (flow channel insert) material with heat conductivity <1W/m K was required to achieve high outlet temperature (700 K). Reversed direction of original flow in DFLL blanket would smooth the flow and reduce heat leakage of PbLi, which formed the idea of improvement. At the extreme condition of duct with steel wall, Lorentz force completely suppressed buoyancy. According to the founding above, we analyzed the MHD buoyant flow in an upside-down DFLL blanket and temperature distribution and heat leakage were significantly improved. This finding would be valuable for liquid blanket thermal hydraulic design.

Convection instability in a downward flow in a vertical duct with strong transverse magnetic field

The downward flow in a vertical duct with one heated and three thermally insulated walls is analyzed numerically using the two-dimensional approximation valid in the asymptotic limit of an imposed strong transverse magnetic field. The work is motivated by the design of liquid metal blankets with poloidal ducts for future nuclear fusion reactors, in which the main component of the very strong magnetic field is perpendicular to the flow direction and very strong heating is applied at the wall facing the reaction chamber. The flow is found to be steady-state or oscillating depending on the strengths of the heating and magnetic field. A parametric study of the instability leading to the oscillations is performed. It is found among other results that the flow is unstable and develops high-amplitude temperature oscillations at the conditions typical for a fusion reactor blanket.

Overview of liquid metal TBM concepts and programs

In support of the ITER Test Blanket Module (TBM) program and coordinated by the Test Blanket Working Group, ITER party members have been focusing on the liquid metal blanket design concepts, most of which have been extensively explored. For the demonstration power reactor (DEMO) design, we will have to accommodate the neutron wall loading and first wall heat flux, breed and extract adequate tritium for the D-T fuel cycle and achieve high coolant outlet temperature for high power conversion efficiency. Most proposed liquid metal TBMs have the potential of achieving similar DEMO goals and requirements. Furthermore, all liquid metal TBMs are to satisfy ITER safety requirements and to be operated and tested within ITER operation scenarios. For the development of liquid metal TBM concepts, many R&D elements are common to a few designs such as the areas of Reduced Activation Ferritic/Martensitic Steel (RAFM, also abbreviated as FS in the following) or V-alloy fabrication, thermal fluid MHD, FS/PbLi, FS/Li and V-alloy/Li compatibility, irradiation effects on different materials, tritium extraction, SiC flow channel insert (FCI) development, etc. With a well-coordinated ITER TBM program, different parties’ R&D activities can supplement and complement each other via collaborations. This paper will present respective designs and R&D programs from seven ITER parties.

A Parametric Study of 3D MHD Flows in Expansions of Rectangular Ducts

In a systematic parametric study 3D MHD flows in expansions of rectangular ducts with different expansion ratios, expansion lengths, and various wall conductivities are analyzed for fusion relevant parameters in order to establish a data base useful for the design of liquid metal blankets for fusion reactors. In currently considered helium-cooled liquid metal blankets the liquid metal velocities are very small so that inertia is often negligible in comparison with the electromagnetic forces. In the core of the flow the major balance of forces establishes between pressure and Lorentz forces while viscous forces are confined to very thin boundary layers along the duct walls. Near the expansion an intense exchange of flow between the upstream and downstream cores with the corresponding side layers is observed. At the expansion a large fraction of the flow is carried by these thin layers along the side walls. This effect becomes more pronounced with decreasing the length of the expansion region. The three-dimensional flow near the expansion gives rise to additional electric currents, which are responsible for higher pressure drop compared with fully developed conditions. This additional pressure drop and the flow partitioning between cores and side layers are investigated in detail depending on the relevant governing parameters.

Crucial issues on liquid metal blanket design

Typical design concepts of liquid metal breeder blankets for power reactors are explained and characterized. The major problems of these concepts are described for both water-cooled blankets and self-cooled blankets. Three crucial issues of liquid metal breeder blankets are investigated. They are in the fields of magnetohydrodynamics, tritium control and safety. The influence of the magnetic field on liquid metal flow is of special interest for self-cooled blankets. The main problems in this field and the status of the related R&D-work are described. Tritium permeation losses to the cooling water is a crucial issue for water-cooled blankets. Methodes for its reduction are discussed. An inherent problem of all liquid breeder blankets is the potential release of activated products in the case of chemical reactions between the breeder material and water or reactive gases. The most important issues in this field are described.

A liquid metal blanket design of RFP fusion reactor — REPUTER-II

A liquid metal cooled RFP fusion core is designed in this study. In order to attain high cooling ability of the first wall without an excessive MHD pressure drop, the return paths of eddy currents induced in the coolant are minimized. Because there are no computer codes capable of analyzing the three-dimensional MHD problems in the blanket, the effects of toroidal field and poloidal field are estimated separately with the assumed streamlines. The total pressure drop through the fusion power core is calculated at only 1 MPa, while the heat transfer coefficient on the first wall is above 25 kW/m 2 . The stress in the first wall is reasonably low. An MHD coil concept, a toroidal field amplifier by the MHD effect, is proposed and showed to be feasible.

Design of Self-Cooled, Liquid-Metal Blankets for Tokamak and Tandem Mirror Reactors

Results of the self-cooled, liquid-metal blanket design from the Blanket Comparison and Selection Study (BCSS) are summarized. The objectives of the BCSS project are to define a small number (about three) of blanket concepts that should be the focus of the blanket research and development (RandD) program, identify and prioritize the critical issues for the leading blanket concepts, and provide technical input necessary to develop a blanket RandD program plan. Two liquid metals (lithium and lithium-lead (17Li-83Pb)) and three structural materials (primary candidate alloy (PCA), ferritic steel (FS) (HT-9), and vanadium alloy (V-15 Cr-5 Ti)) are included in the evaluations for both tokamaks and tandem mirror reactors (TMRs). TMR is of the tube configuration similar to the Mirror Advanced Reactor Study design. Analyses were performed in the following generic areas for each blanket concept: MHD, thermal hydraulics, stress, neutronics, and tritium recovery. Integral analyses were performed to determine the design window for each blanket design. The Li/Li/V blanket for tokamak and the Li/Li/V, LiPb/LiPb/V, and Li/Li/HT-9 blankets for the TMR are judged to be top-rated concepts. Because of its better thermophysical properties and more uniform nuclear heating profile, liquid lithium is a better coolant than liquid 17Li83Pb. From an engineeringmore » point of view, vanadium alloy is a better structural material than either FS or PCA since the former has both a higher allowable structural temperature and a higher allowable coolant/structure interface temperature than the latter. Critical feasibility issues and design constraints for the self-cooled, liquid-metal blanket concepts are identified and discussed.« less