Influence of helium cooling channels on magnetohydrodynamic flows in the HCLL blanket

One of the blanket concepts proposed to be tested in ITER as part of the test blanket module program of the European Union is the helium cooled lead lithium blanket design. In this configuration the so called breeder units are arranged in an array, separated by a stiffening grid, to form blanket modules. The deposited thermal energy is removed by helium flowing at high pressure and speed in channels integrated both in the walls and in cooling plates that subdivide the breeder units into flat ducts where the lead lithium circulates under the influence of the strong plasma confining magnetic field. This gives rise to magnetohydrodynamic (MHD) phenomena whose effects on flow distribution have to be investigated to evaluate the performance of the proposed design. The established MHD flow is affected by the presence of helium channels in cooling and stiffening plates that results in non-homogeneous wall conductance.In support to the conceptual study of a liquid metal blanket, numerical investigations of fully developed MHD flows in a central cross-section of breeder units have been performed, taking into account both the presence of helium channels in the walls and the multi-channel effects caused by the exchange of currents through walls separating different fluid domains.     

3D thermo-fluid MHD simulation of single straight channel flow in LLCB TBM

India is developing lead lithium cooled ceramic breeder (LLCB) blanket for its DEMO fusion reactor. The mock-up blanket (TBM), using this concept, will be tested in ITER for its tritium breeding and high-grade heat extraction efficiency. In this TBM, pressurized helium is used to remove the heat from first wall, top and bottom plates of TBM. The Pb–Li is used to extract heat from the breeder zones. The flow of Pb–Li with average velocity 0.1 m/s inside the channel can be significantly modified due to MHD effects, which arise because of the presence of strong toroidal magnetic field. A numerical approach is established to capture this flow modification at higher Hartmann numbers (≥20,000). As a validation part of the developed code, MHD phenomenon is studied in 2-D square geometry and numerically obtained velocity profile is compared with available Hunt's analytical results. Thermo-fluid MHD analysis using this code, has been carried out for single rectangular duct of LLCB TBM. The heat transfer has been studied by keeping hot breeders at both sides of the flow channel. The results suggest modification in steady state MHD velocity profile as the liquid flows along the flow length. However, the temperature in various zone remains well within the maximum allowable limit.     

Liquid metal magnetohydrodynamic flows in manifolds of dual coolant lead lithium blankets

An attractive blanket concept for a fusion reactor is the dual coolant lead lithium (DCLL) blanket where reduced activation steel is used as structural material and a lead lithium alloy serves both to produce tritium and to remove the heat in the breeder zone. Helium is employed to cool the first wall and the blanket structure.Some critical issues for the feasibility of this blanket concept are related to complex induced electric currents and 3D magnetohydrodynamic (MHD) phenomena that occur in distributing and collecting liquid metal manifolds. They can result in large pressure drop and undesirable flow imbalance in parallel poloidal ducts forming blanket modules.In the present paper liquid metal MHD flows are studied for different design options of a DCLL blanket manifold with the aim of identifying possible sources of flow imbalance and to predict velocity and pressure distributions.     

Influence of surface oxidation on electric potential measurements in MHD liquid metal flows

Experimental investigations for magnetohydrodynamic flows in rectangular ducts are performed using GaInSn as model fluid. Measurements of electric potential on channel walls and inside the flow show reproducible discrepancies compared to analytical results. These discrepancies can be ascribed to the formation of oxide layers causing a contact resistance between the electrically conducting duct walls and the liquid metal. An exact analytical solution for pressure drop, velocity and potential distributions has been derived taking into account the presence of a contact resistance. Analytical results for velocity and potential profiles and for pressure drop are discussed for different values of contact resistance and strength of the applied magnetic field. A comparison of measured potential with data from the analytical solution allows estimating the order of magnitude of the contact resistance in the present experiments.     

Effect of a magnetic field on stability and transitions in liquid breeder flows in a blanket

We review previous studies on instabilities and transitions in magnetohydrodynamic flows in a special context of liquid-metal blanket applications. In the past, possible transitions in blanket flows were mostly attributed to instabilities in the Hartmann layers. More recent studies show, however, that the side layers can experience instabilities at sufficiently lower Reynolds numbers. This suggests that in the blanket flows, the appearance of turbulence can most likely be related to the side rather than Hartmann layers. Various factors that may affect stability in blanket flows have been discussed. In particular, buoyancy forces can result in potentially unstable inflectional velocity profiles. First computational results, illustrating possibility of instabilities and quasi-two-dimensional turbulence in vertical mixed-convection flows heated volumetrically are presented.     

Effect of electromagnetic coupling on MHD flow in the manifold of fusion liquid metal blanket

In fusion liquid metal (LM) blanket, magnetohydrodynamics (MHD) effects will dominate the flow patterns and the heat transfer characteristics of the liquid metal flow. Manifold is a key component in LM blanket in charge of distributing or collecting the liquid metal coolant. In this region, the complex three dimensional MHD phenomena will be occurred, and the velocity, pressure and flow rate distributions may be dramatically influenced. One important aspect is the electromagnetic coupling effect resulting from an exchange of electric currents between two neighboring fluid domains that can lead to modifications of flow distribution and pressure drop compared to that in electrical separated channels. Understanding the electromagnetic coupling effect in manifold is necessary to optimize the liquid metal blanket design.In this work, a numerical study was carried out to investigate the effect of electromagnetic coupling on MHD flow in a manifold region. The typical manifold geometry in LM blanket was considered, a rectangular supply duct entering a rectangular expansion area, finally feeding into 3 rectangular parallel channels. This paper investigated the effect of electromagnetic coupling on MHD flow in a manifold region. Different electromagnetic coupling modes with different combinations of electrical conductivity of walls were studied numerically. The flow distribution and pressure drop of these modes have been evaluated.     

Upgrading the data acquisition and control systems of the European Breeding Blanket Test Facility

The EBBTF (European Breeding Blanket Test Facility) experimental plant is a key component for the development of the breeding blankets (TBMs test blanket modules, HCLL helium cooled lithium lead and HCPB helium cooled pebble bed types) used by ITER. EBBTF is an experimental plant which provides the double breeding/cooling loops (liquid metal and gas) required for HCLL testing. EBBTF is composed of four subsystems (TBM, IELLLO integrated European lead lithium loop, HE-FUS3 helium fusion loop, version 3 and helium compressor build by ATEKO) with dedicated control systems realized with hardware/software combinations covering 15 years (1995–2010) time span. At the end of 2010 we began to upgrade the HE-FUS3 data acquisition control systems (DACS) replacing the obsolete PLC Siemens S5 with National Instruments Compact FieldPoint and LabVIEW. The control room has been completely reorganized using high resolution monitors and workstations linked with standard Ethernet interfaces. The data acquisition, control, safety and SCADA software has been completely developed in ENEA using LabVIEW. In this paper we are going to discuss the technical difficulties and the solutions that we have used to accomplish the upgrade.     

强磁场作用下液态锂在矩形通道中的流动研究

对高速液态金属锂在强磁场作用下沿着非扩散矩形型通道的流动进行了分析研究 ,通过解析分析 ,推导得到了控制电场和流场的由泊松 (Poisson)方程和亥姆霍兹 (Helmholtz)方程组成的方程组 ,并且编制了求解该方程组的程序 PHsolver;根据边界的壁面函数处理 ,用PHsolver求解得到了强磁场作用下在非扩散型矩形通道中电流密度场的分布和流场的分布 ,其中流速分布呈现为马鞍型分布。     

Laminar pipe flow at the entrance into transverse magnetic field

High-resolution numerical simulations are conducted to analyze transformation of a liquid metal flow in a pipe at the entrance into a transverse magnetic field. The case of laminar flow, perfectly insulating pipe walls, and Hartmann number up to 200 is considered. The simulations reveal detailed structure of velocity and electric current fields and distribution of forces with particular attention given to the flow with an M-shaped velocity profile. They also establish criteria for accurate computations of laminar magnetohydrodynamic flows in strong non-uniform magnetic fields.     

Preliminary numerical analysis of MHD flow of DFLL-TBM on the single coolant stage

The liquid lithium–lead (PbLi) breeder blanket concept has been explored extensively due to their potential attractiveness. To check and validate the feasibility, the China dual-functional lithium lead test blanket module (DFLL-TBM) system, which is designated to demonstrate the integrated technologies of both He single coolant (SLL: single-cooled lithium lead) and He–LiPb dual-coolant (DLL: dual-cooled lithium lead) blankets, is proposed for test in ITER. One of the key feasibility issues is the impact of liquid metal MHD effect which will influence the pressure drop, flow distribution, and heat transfer in a DFLL-TBM.To reduce MHD effect, an electrically insulating coating is applied onto the inner surface of the flow channel for single coolant blanket. In this work, a preliminary numerical study of MHD flows in a simplified DFLL-TBM model on the single coolant stage has been carried out to assess the performance of such a concept with regard to the above mentioned MHD problems and constraints. The flow distribution and MHD pressure drop of LiPb flow in the SLL stage TBM are analyzed.     

A new cooling scheme for the HCLL TBM

The Helium Cooled Lithium Lead (HCLL) blanket is one of the two blanket concepts selected by the European Union to be tested in ITER. It is based on the use of Eurofer as structural material, helium as coolant and eutectic lithium–lead as breeder/neutron multiplier material. The design of the corresponding Test Blanket Module (TBM) for ITER has undergone several revisions in the last years. This paper presents an alternative cooling scheme for the HCLL-TBM, where the First Wall (FW) is cooled by vertical (poloidal) instead of horizontal (toroidal) channels. New Finite Element models have been developed and thermal and thermo-hydraulical analyses of the new design have been performed. Results show that the new cooling scheme presents several advantages with respect to the previous one: (i) the total number of cooling channels in the FW can be reduced; (ii) the overall pressure drops in one cooling channel are lower; (iii) the temperature profile in the breeding zone is more uniform.     

Numerical study of corrosion of ferritic/martensitic steels in the flowing PbLi with and without a magnetic field

A computational suite called TRANSMAG has been developed to address corrosion of ferritic/martensitic steels and associated transport of corrosion products in the eutectic alloy PbLi as applied to blankets of a fusion power reactor. The computational approach is based on simultaneous solution of flow, energy and mass transfer equations with or without a magnetic field, assuming mass transfer controlled corrosion and uniform dissolution of iron in the flowing PbLi. First, the new tool is applied to solve an inverse mass transfer problem, where the saturation concentration of iron in PbLi at temperatures up to 550 °C is reconstructed from the experimental data on corrosion in turbulent flows without a magnetic field. As a result, a new correlation for the saturation concentration C^S has been obtained in the form C^S = e^{13.604–12975/T}, where T is the temperature of PbLi in K and C^S is in wppm. Second, the new correlation is used in the computations of corrosion in laminar flows in a rectangular duct in the presence of a strong transverse magnetic field. As shown, the mass loss increases with the magnetic field such that the corrosion rate in the presence of a magnetic field can be a few times higher compared to purely hydrodynamic flows. In addition, the corrosion behavior was found to be different between the side wall of the duct (parallel to the magnetic field) and the Hartmann wall (perpendicular to the magnetic field) due to formation of high-velocity jets at the side walls. The side walls experience a stronger corrosion attack demonstrating a mass loss up to 2–3 times higher compared to the Hartmann walls. Also, computations of the mass loss are performed to characterize the effect of the temperature (400–550 °C) and the flow velocity (0.1–1 m/s) on corrosion in the presence of a strong 5 T magnetic field prototypic to the outboard blanket conditions.     

Influence of flow channel insert with pressure equalization opening on MHD flows in a rectangular duct

Direct simulation of 3D MHD flows in a duct with flow channel insert (FCI) relevant to R&D of fusion blanket has been conducted based on an electrical potential formula by using a consistent and conservative scheme. Comparison study of the pressure and velocity distributions of liquid metal in a poloidal duct with FCI, which has pressure equalization slot (PES) and pressure equalization holes (PEHs) with the same total area at the corresponding walls, is conducted. Both the PES and the PEHs have two kinds of locations, either in a Hartmann wall or in a side wall. 3D pressure and velocity distributions of the different cases have been given.     

Code Validation for Magnetohydrodynamic Buoyant Flow at High Hartmann Number

In liquid metal fusion blanket, the non-uniform volumetric heat deposited by the fusion neutrons leads to the non-uniform density distribution of liquid metal. With the force of gravity, buoyant flows would happen. In the fusion blanket where the magnetic field is up to 4T or even higher and the Hartmann number is ~10⁴, these effects caused by the buoyancy will significantly influence the flow and heat transfer characteristics. In this paper, a module for magnetohydrodynamic (MHD) buoyant flow at high Hartmann number was added to the code MTC. A current density conservative scheme was used to ensure the conservation of current, and the Boussinesq model was used to simulate the buoyancy force. This code was validated by two benchmarks, and the results showed that it can give an accurate simulation for MHD buoyant flows. Main characteristics of buoyancy effects of MHD flows were investigated, and the suppression of buoyant convection by strong magnetic field was studied to understand how the direction of magnetic field and electric conductivity of wall affects the suppression.     

Numerical investigation of liquid metal magnetohydrodynamic flow in multilayer flow channel inserts

In the high temperature liquid metal blanket of fusion-based hydrogen production reactor (named FDS-III), there is a remarkable feature that the multilayer flow channel inserts (MFCI) as function component are put into the breeding zone. The low thermal conductivity of MFCI can prevent the internal PbLi's heat conduct to the outside. So the outlet temperature can achieve high temperature around 1000 °C for high efficient production of hydrogen. However, the flow of liquid metal meandering through the MFCI will cause complex magnetohydrodynamic (MHD) effect under the strong fusion magnetic field. Liquid metal MHD effect is a key issue which should be concerned in high temperature breeder blanket (HTL). In this work, a numerical study was carried out to investigate the MHD effect of liquid metal PbLi in the MFCI. The MHD flows with typical modified geometry of the HTL MFCI were considered. The characteristics of flow and induced current fields were analyzed, and the pressure drop was evaluated. It also can be seen that the conductivity of the MFCI will have great impact on liquid metal flow's current and velocity distributions.     

Design for a high power-density Astron reactor

A liquid lithium blanket surrounding the plasma volume is described. The liquid lithium flows along magnetic flux tubes at a high speed. There is no vacuum wall between the blanket and the plasma. The E-layer of relativistic particles within which the plasma is confined serves as a vacuum wall protecting the plasma from the lithium vapor, which is continuously produced at the surface of the blanket, by ionizing the lithium atoms and ejecting the same along open magnetic lines. The heat load at the surface of the blanket generated by 14 MeV neutrons can be several hundred MW per square meter.Work performed under the auspices of the U.S. Atomic Energy Commission.Deceased September 24, 1972.     

The EU TBM systems: Design and development programme

This paper presents the status of the design and of the development programme of the two test blanket systems (TBSs) based on the blanket concepts supported by the EU, namely the helium cooled lithium lead (HCLL) and helium cooled pebble bed (HCPB) concepts.Both the test blanket modules (TBMs) box design and the associated systems (Helium Cooling Systems, PbLi loop for the HCLL system, helium processing systems for tritium extraction, etc.) have been revised and, where needed, modified according to the assumption that one ITER equatorial port could be available for testing the two European test blanket modules (TBMs).According to EU TBMs programme, two reliable test blanket systems shall be ready for installation on the first day of ITER operation. In order to comply with this ambitious objective, six EURATOM associates who have sustained the TBM program so far have joined themselves in a consortium aiming to ensure an efficient management of the project tasks and exploit specific competences enhancing potential synergies. The consortium objectives and development programme are summarised in the paper.     

Tritium management and anti-permeation strategies for three different breeding blanket options foreseen for the European Power Plant Physics and Technology Demonstration reactor study

In DT fusion reactors like DEMO, the commonly accepted tritium (T) losses through the steam generator (SG) shall not exceed about 2 mg/d that are more than 5 orders of magnitude lower than the T production rate of about 360 g/d in the breeding blanket (BB). A very effective mitigation strategy is required balancing the size and efficiency of the processes in the breeding and cooling loops, and the availability and efficiency of anti-permeation barriers. A numerical study is presented using the T permeation code FUS-TPC that computes all T flows and inventories considering the design and operation of the BB, the SG, and the T systems. Many scenarios are numerically analyzed for three breeding blankets concepts – helium cooled pebbles bed (HCPB), helium cooled lithium lead (HCLL), and water cooled lithium lead (WCLL) – varying the T processes throughput and efficiency, and the permeation regimes through the BB and SG to be either surface-limited or diffusion-limited with possible permeation reduction factor. For each BB concept, we discuss workable operation scenarios and suggest specific anti-permeation strategies.     

Design of a multipurpose laboratory scale apparatus for the investigation of hydrogen isotopes in PbLi and permeation technologies

The knowledge of the tritium transport parameters in lead lithium is fundamental for the design of the HCLL (helium cooled lead lithium) blanket. In fact, the inventory of tritium in fusion reactors blankets and the permeation of tritium into the blanket coolant, with the consequent leaks toward the environment, are strongly depending on its solubility and diffusivity in the lead alloy PbLi. Several experiments, devoted to investigate the function linking the tritium solubilised in lead lithium with the corresponding tritium partial pressure at equilibrium, were carried out in the past, but significant uncertainties still remain.A detailed analysis of the past experimental works is carried out in this paper with the aim to investigate the main problems occurred in the facilities used to measure the tritium solubility in PbLi that caused such a big spread in the achieved results. On the basis of this analysis, a new a multipurpose laboratory scale apparatus has been designed. The apparatus is able to measure the tritium solubility and diffusivity in PbLi in the range of temperature 300–550 °C and it will be operated with hydrogen partial pressure in the range 10²–10⁴ Pa. The facility can work with desorption and absorption technique.Moreover, the apparatus has been designed to allow the testing of H/D concentration sensors in Pb–15.7Li in operative conditions relevant to the HCLL–TBM and the characterisation of hydrogen permeation barrier.     

Natural circulation of electrically conducting liquids in fusion reactor blankets

A simple model has been developed for heat transfer in fusion reactor blankets with liquid breeding regions, allowing for natural circulation and the presence of strong magnetic fields. The results have been compared with the limited information available.For typical fusion blanket dimensions and temperature differences, natural circulation can be the dominant heat transfer mechanism in the molten salt flibe even over 10 Tesla magnetic field strength; it will increase heat transfer appreciably in the liquid lithium-lead mixture Li₁₇Pb₈₃ for magnetic field strengths less than about 10 Tesla; and can be neglected in liquid lithium if the magnetic field is over 1 Tesla.