Flow Channel Insert Research Articles

Unsteady Mixed Convection Flows in a Rectangular Duct and Dynamical Behaviors of Flow Channel Insert

Buoyancy-assisted upward MHD flows and dynamical behaviors of flow channel insert (FCI) in the dual-coolant lead-lithium (DCLL) blanket are studied numerically. Based on our internally developed and validated solver, the dynamical behaviors of magneto-thermo-fluid-structure coupled multiphysical field are investigated. A large amplitude, low frequency, and quasiperiodic unsteady reverse flow at high Re (31000), high Gr (3.5×1011), and moderate magnetic field (0.7~1.7T) is found in the DCLL blanket. This intricate phenomenon has been discovered for the first time, representing a combination of separate experimental results from Melnikov et al. (2016) and Khanal and Lei (2012). In our study of this large amplitude, low frequency, and quasiperiodic unsteady reverse flows, the importance of the cold helium gas to the instability of fluid flow in the bulk region and the thermal conductivity of the FCI to convection structure and instability are first found and recognized. Additionally, we take into account the effects of the temperature field and flow field on structural deformation and mechanical behavior of FCI, and we have discovered several intriguing phenomena, such as (1) the stability of fluid flow in the bulk region depends on the strength of the heat source, the magnitude of the magnetic field, and thermal conductivity of FCI; (2) the instability and periodicity of the fluid flow are primarily related to the unsteady reverse flow, which rises up and falls down periodically in the bulk region; (3) the physical mechanism of unsteady flow influenced by reverse flow, pressure drop, and Lorentz force has been concluded. It has been discovered that the breakdown of a reverse flow vortex causes a rapid reduction in pressure drop. (4) To avoid this phenomenon in engineering, a phase map of unsteady and steady flows in the DCLL blanket has been created. (5) The quasiperiodic characteristics of solid (flow channel insert) affected by flow are found and analyzed.

Fabrication Aspects and Performance Characterization of α-Al2O3/AlPO4 Based Sandwich Configuration Flow Channel Inserts and Coatings for High Temperature Liquid Metal Applications

Abstract Liquid metals (LMs) exhibit several key characteristics justifying their utilization as coolants and breeders for nuclear fusion reactors and advanced fission reactors. In fusion reactors, the LMs confront an exorbitantly high flow retarding force, due to the magneto-hydro-dynamics (MHD) effect, imposing significant demands on the pumping power and designs of ancillary coolant systems. Corrosion of structural materials leading to activated corrosion products and coolant chemistry control are some of the vital issues common to both fusion and fission reactors employing liquid lead (Pb) and its alloys. To address these concerns, different technological solutions such as flow channel inserts (FCIs) and high temperature compatible corrosion resistant coatings are being investigated to provide a chemical and/or electrical isolation between the LM and structural material for advanced reactors. In this study, three different prototype geometries (circular, square, and 90 deg bend) of steel-insulator-steel sandwich FCIs are fabricated for fusion reactor applications and an extensive characterization of the electrical insulation is performed over an operating temperature range of 100 °C–600 °C. Welding trials and pneumatic pressure tests up to 10 kg/cm2 (g) are performed on the assemblies to validate the electrical and mechanical integrity over typical fusion reactor operational regime. This paper presents detailed fabrication aspects along with quantitative estimations of insulation filling density, electrical insulation performance and, for the first time, a detailed systematic study of insulation degradation resulting from the combined effects of tungsten inert gas (TIG) welding, exposure to pressure and machining operations on these FCIs. The paper also provides critical details derived from the metallurgical examinations and visual observations from the destructive tests executed on the prototypes. Further, from an implementation perspective toward Lead-cooled Fast Reactors (LFRs), a preliminary feasibility assessment of the α-Al2O3/AlPO4 coating is performed through thin film deposition trials on planar and non-planar substrates followed by mechanical characterizations, such as coating thickness, surface roughness, adhesion strength and microhardness. Metallurgical analyses are presented and discussed to assess Pb ingress after 700 h of continuous exposure to molten Pb alloy at 300 °C–400 °C.

Hydrodynamics and electrical insulation of PbLi flow with SiC flow channel inserts in a strong magnetic field

Experimental and numerical research in a strong magnetic field is described in this article testing silicon carbide (SiC) flow channel inserts (FCI) in lead-lithium (PbLi) liquid metal flow. The study aims to further develop the High-Temperature Dual-Coolant Lead-Lithium nuclear fusion blanket concept by testing new variations of SiC inserts operating in the relevant electromagnetic conditions. These inserts act as electrical insulators in magnetohydrodynamic lead-lithium flow and can also play the role of the thermal insulator in the potentially real fusion environment. The liquid metal pressure and integral flowrate measurements were performed on up to 5T DC magnetic field created by a superconducting magnet at high temperatures up to 700 °C, which is close to the real fusion environment. Comparisons of several cases with and without inserts are provided, demonstrating their impact on hydraulic resistance. Additionally, electrical potential distribution is recorded on the lead-lithium channel walls, which can be used to evaluate the character of liquid metal velocity distribution in the lead-lithium channel.

Relevance of Tritium Breeder Irradiation Testing in a Fusion Prototypic Neutron Source

A fusion prototypic neutron source (FPNS) will play a fundamental role in testing and developing fusion materials that can withstand the harsh fusion environment. A thorough assessment is conducted to determine whether blanket materials would benefit from FPNS testing. Because of the cross sections for the various blanket materials, lithium-containing materials can generally be tested adequately using existing fission irradiation capabilities instead of waiting for or relying solely on future FPNS experiments. However, non-lithium blanket materials, such as beryllium multipliers and flow channel inserts, should be tested under a fusion neutron spectrum.

Experimental setup for study of mechanical performance of materials in liquid Pb-16Li and first results

Dual Coolant Lithium Lead (DCLL) Breeding Blanket, which is using the eutectic lead-lithium alloy (Pb-16Li) as tritium breeder, neutron moderator and coolant, is being developed in the frame of the EUROfusion project. Flow channel inserts (FCI) are insulating components embedded along the Pb-16Li channels inside the DCLL breeding blanket modules developed to minimize the magnetohydrodynamic pressure drop and heat losses. There is an effort to modify the originally designed steel-ceramic-steel layered structure of FCI by eliminating the steel protective layer leading to simple steel-ceramic structure. In this arrangement, the ceramic is directly exposed to liquid Pb-16Li. Demanding operating conditions of the DCLL blanket, in particular elevated temperatures, may give a rise to thermomechanical stresses leading to component failure. Therefore, the assessment of mechanical behaviour of the material in direct contact with Pb-16Li is of primary interest.To study the mechanical properties of the material exposed to corrosive environment of Pb-16Li at elevated temperatures, a dedicated experimental setup was designed. Three-point flexural test is adopted to evaluate the flexural stress-strain material response. Since the experimental procedure is performed in liquid Pb-16Li at high temperatures with an inert atmosphere, the mechanical test takes place in an isolated testing chamber filled with molten Pb-16Li transferred from the melting chamber prior the mechanical test. A specificity of the presented facility is its capability of material testing of three samples within one testing procedure in Pb-16Li at temperatures up to 650 °C.

Large Component Simulation of an Inboard Sector of a Dual-Coolant Lead-Lithium Blanket

Advances in high-performance computing now enable the engineering evaluation of large blanket components from a systems perspective at the beginning of a normal design cycle. As an example, we discuss the computational fluid dynamics (CFD) involved in characterizing the thermal performance of an entire 22.5 toroidal sector of a dual-coolant lead-lithium blanket with particular attention to the integrated manifolding and flow distributions. The inboard sector is roughly 7 m tall, has 321 first-wall helium-cooled channels, and five parallel PbLi breeder channels complete with insulating SiC flow channel inserts. A finite volume model was developed with various degrees of mesh refinement from 36 to 187 million cells to perform the flow calculations on disparate fluids with conjugate heat transfer in the solid. Steady-state CFD calculations were performed using a realizable k-ε turbulence model. Simplifications include a uniform applied surface heat flux and a one-dimensional radial volumetric neutron heating profile. Constant material properties were used for the F82H reduced-activation ferritic martensitic (RAFM) steel walls, SiC flow channel inserts, and the PbLi breeder. Ideal gas behavior was assumed for the helium, which includes compressibility. Helium mass flows of 54 kg/s at 8 MPa and PbLi flows of 3 kg/s at 101 kPa supply the sector, both at an inlet temperature of 350°C. This early model is not optimized; however, it reveals important features not obvious in a conglomeration of smaller independent models. For example, all the manifolding was included to evaluate flow distributions throughout the full component. Submodels were only used to obtain the convective heat transfer coefficients (HTCs) inside the helium first-wall channels equipped with enhancement vanes that allow the first wall to handle 0.8 MW/m2 of plasma heat flux with the aim of keeping bulk RAFM steel temperatures near the creep-fatigue limit of 550°C. Average HTCs obtained from these detailed submodels were then used in the large model to predict thermal performance without incurring the meshing overhead from the thousands of internal vanes. Although much progress was made, initial results indicate that more must be done to further reduce hot spots on the first wall, minimize pressure drops, and provide optimal flow distributions.

Radiological characterization of ceramic materials considered for the HT-DCLL DEMO reactor

The recent evolution of the Breeding Blanket (BB) Dual Coolant Lithium-Lead (DCLL) concept for the European DEMO from a low temperature (LT) multi-module segment (MMS) approach, limited by the thermal range tolerated by EUROFER, to an advanced high temperature (HT) single-module segment (SMS) architecture, is allowed by the consideration of ceramics and composite materials as main structural material rather than just as thin Flow Channel Inserts (FCI). The amount of the ceramic as main structure instead than as a FCI in the whole reactor could be of several tonnes generating concern regarding the radiological behaviour of such component and the consequent generated waste. For that, a preparatory assessment considering ideal “pure” ceramics has been performed towards a preliminary selection of the structural material, among others, under the criteria of maintenance operations and waste management. To complement such study additional analyses have been carried out considering not only the intendent element but also dopant and impurities which often give rise to significant additional activation. For both the theoretical compositions as well as the industrial ones, with a certain amount of impurities, activation calculations have been performed using the ACAB inventory code. Hence, total beta-gamma activity, specific activity for different nuclides, decay heat and surface gamma dose rate have been analysed with reference to the IAEA and SEAFP-2 standards for waste and handling classifications and to the specific regulations of the near-surface repository El Cabril (Córdoba, Spain). According to El Cabril regulation, pure SiC and TiC would be the best of the options considered since they would be accepted in Level 1 LILW (under detritiation for SiC). This may not be true for industrial compositions with impurities (Level 2), nor according to other standards. Pure zirconia is also a promising option, so further work is ongoing for zirconia and doped zirconia materials.

Fabrication and characterization of SiC sandwich material for Flow Channel Inserts in HT-DCLL blanket by gel casting

Flow Channel Inserts (FCIs) are key elements in the high temperature DCLL blanket concept since they provide the required thermal insulation between the He-cooled structural steel and the hot PbLi flowing at a maximum temperature of 700 °C, and the necessary electrical insulation to minimize magnetohydrodynamic (MHD) effects. In this paper, the use of SiC-sandwich material for FCIs consisting of a porous SiC core (thermal and electrical insulator) covered by a dense Chemical Vapor Deposition (CVD) SiC layer (protection against PbLi infiltration) has been studied. Lab-scale FCI prototypes were produced by the gel casting method and characterized in terms of thermal and electrical conductivities (the latter before and after exposure to ionizing radiation) and flexural strength. Corrosion tests under flowing PbLi at 500–700 °C in presence of a magnetic field up to 5 T were performed obtaining promising results regarding the reduction of MHD pressure drop and the compatibility of SiC and PbLi under dynamic conditions. Additionally, thermomechanical finite elements simulations were performed in a 3D channel geometry to identify black spots regarding thermal stresses.

Hydrodynamics and Electrical Insulation of Pbli Flow with Sic Flow Channel Inserts in a Strong Magnetic Field

Hydrodynamics and Electrical Insulation of Pbli Flow with Sic Flow Channel Inserts in a Strong Magnetic Field

Chemical compatibility of bulk alumina in flowing PbLi alloy under magnetic field

Electrically insulating flow channel inserts (FCI) may be needed in liquid-based breeding blanket concepts to electrically decouple the metal flow from the strong magnetic field in a future fusion reactor. Although the magnetohydrodynamic simulation demonstrates a reduction of the pressure drop when a sandwich-like steel-alumina-steel FCI is employed, the tritium production efficiency in the breeding zone of a breeding blanket is limited to 550 °C due to the steel corrosion. Previous theoretical thermomechanical analyses point out the possible occurrence of induced interfacial stresses between the steel and the ceramic part. Both factors motivate the actual FCI development towards the avoidance of the steel protection. Therefore, a chemical compatibility study between high density alumina and hot PbLi was addressed during this experimental work by using the Energy Dispersive X-ray spectroscopy elemental analysis coupled to a scanning electron microscope. Analyzed samples were previously tested during 1000 hs in an experimental PbLi loop at 550 °C affected by a 1.35 T magnetic field. Results allow concluding the high confidence to expose the insulator directly to the liquid flow.

Electrical resistivity behaviour of alumina flow channel inserts in PbLi

Abstract In order to minimize the pressure drop induced on a liquid metal flowing in a strong magnetic field, the insertion of ceramic insulators in the PbLi pipes of a fusion breeding-blanket is being seriously considered. These components are known as Flow Channel Inserts. Fully dense alumina ceramic specimens in the shape of furnace crucibles were supplied to the Research Centre Řež, Czech Republic, for electrical measurements at close to operational conditions. The aim of the experiments was to monitor the alumina insulator’s behaviour with time and temperature in an intimate contact with hot PbLi alloy. Therefore, several set of PbLi cooling-heating cycles between 200 and 430 °C were programmed while the alumina resistance was recorded. After the test, the chemical compatibility between the alumina and the alloy was examined by means of the microstructural study of the cut pieces. Under polarization condition and close to the PbLi operational temperature, the FCI required insulating properties can be concluded. Since the calculated conductivity values are comparable with that obtained in vacuum condition, the absence of influence in the alumina behaviour of both the previously applied thermal treatment and the contact with the hot static alloy is therefore deduced. As concluded from SEM and EDX analyses, the initial alumina microstructure was found unaltered after the high temperature tests performed in contact with PbLi, concluding the suitable chemical compatibility between the ceramic and the hot metal alloy.

Toward full simulations for a liquid metal blanket: MHD flow computations for a PbLi blanket prototype at Ha ∼ 104

Numerical simulations of liquid metal (LM) magnetohydrodynamic (MHD) flows in a prototypical dual coolant lead lithium (DCLL) blanket module have been performed under conditions relevant to a real LM blanket system, i.e. strong magnetic field of 5 T (Hartmann number Ha ∼ 104) and poloidal flow velocity of 0.1 m s−1 (Reynolds number Re ∼ 105). The proposed blanket model includes all essential sub-components of a real LM blanket: radial supply ducts, inlet and outlet manifolds, multiple poloidal ducts and a U-turn zone. The computations were performed using a DNS-like finite-volume code on a very fine mesh of ∼ 320 × 106 cells to accurately capture all flow features. Four cases have been simulated, including: Case 1 for electrically conducting walls, Case 4 for non-conducting walls, and Cases 2 and 3 with partial SiC FCIs electrical insulation of the blanket conduits using silicon carbide flow channel inserts placed at selected locations. In these four cases, the computed MHD flows were analyzed for: (1) MHD pressure drop, (2) flow distribution, (3) flows in particular blanket components, (4) 3D and flow development effects, and (5) unsteady flows. Many important conclusions have been made, regarding effectiveness of the FCI to reduce the MHD pressure drop, flow balancing in the parallel channels, characteristic flow patterns in all blanket sub-components, electromagnetic coupling between the flows, 3D MHD effects, flow development length, and unsteady effects. This study is limited to purely MHD flows. Next study will focus on a DCLL blanket with a volumetric heating.

Nonlinear effects of FCI electrical conductivity on the MHD flow in DCLL blanket

In a Dual Coolant Lead Lithium (DCLL) blanket, flow channel insert (FCI) with low electrical conductivity and low thermal conductivity is introduced to reduce the MHD pressure drop and improve the heat transfer efficiency. In the present work, we aim at performing a direct simulation of the magneto-thermal-fluid-structure multi-physical fields in a typical poloidal duct with different electrical conductivities of FCI, using a coupled computing platform including CFD and the finite element method (FEM), to study the pressure field, velocity field, temperature field, as well as the deformation and stresses of FCI. A consistent and conservative scheme and PISO method on an unstructured collocated mesh are employed to solve the incompressible Navier–Stokes equations with the Lorentz force included. The results show that: with the increasing of FCI's electrical conductivity (σFCI), the pressure reduction efficiency becomes lower; the pressure difference between the FCI's inside patches and the corresponding outside patches increases after an initial reducing; two jets appear in the side gap and the one near FCI develops to a reverse flow; the variation of the temperature difference across FCI and the interface temperature of first wall (FW) is non-monotonic; the cause of nonlinear variation of thermal deformations and stresses of FCI with electrical conductivity results from the nonlinear effect of Lorentz force on the liquid metal velocity. This work is the theoretical basis of blanket design.

Analysis of flow channel insert deformations influence on the liquid metal flow in DCLL blanket channels

Abstract The dual coolant lithium lead (DCLL) is a candidate to be an effective breeding blanket (BB) concept for nuclear fusion technologies. One critical point of this design is the magnetohydrodynamic (MHD) effects involving Lorentz damping force which produces relevant pressure drop in the eutectic flow. In the framework of the European DEMO, the application of sandwich-like steel–alumina–steel flow channel insert (FCI) seems to be the best solution to reduce the pressure drop by electrically decoupling the liquid PbLi from the Eurofer walls. The impact of the FCI on the PbLi velocity profile is analyzed in this work with a CFD solver implemented on OpenFOAM. Under the assumption of non-buoyant fully developed channel flow the temperature map in the channel is computed. Based on the temperature field, the induced deformation is evaluated. The effects of the FCI deformation and possible rupture of the FCI on the velocity profile and on the corresponding pressure drop are then parametrically investigated. Results show that the deformation of the FCI and the possible break in the Hartmann wall do not lead to significant variations in the pressure drop from the case of intact FCI in a wide range of interaction parameters.

Experimental investigation of liquid metal MHD flow entering a flow channel insert

Insulating flow channel inserts (FCI) in ducts of liquid metal blankets decouple electrically the fluid domain from the conducting thick-walled structure. They interrupt current paths across well-conducting walls and thereby reduce significantly magnetohydrodynamic (MHD) pressure drop. Pipe flow of an electrically conducting liquid metal entering a region where walls are covered by a FCI is investigated experimentally under the influence of a strong uniform magnetic field. The abrupt change in wall conductivity leads to 3D MHD effects that are studied by measuring pressure and electric potential distribution along the duct wall. It is shown that FCIs may reduce pressure drop by at least one order of magnitude but 3D effects at the entrance of FCIs may reduce the efficiency of the insulating inserts by some degree.

On the electrical properties under irradiation of porous SiC prepared by sacrificial template technique

Flow Channel Inserts are the key elements in the DCLL breeder blanket concept for the required electrical insulation to reduce magnetohydrodynamic effects. Porous SiC materials produced for this purpose by a novel and inexpensive method which allows one to obtain different porosity percentage and physical properties are characterized regarding electrical conductivity and considering radiation effects. Insulating properties are verified before, during, and after 1.8 MeV electrons up to 140 MGy. Results indicate good stability under high temperature, and fusion-relevant ionizing radiation dose rates. However, enhanced electrical conductivity is observed when a corrosion and permeation-protective dense SiC layer is deposited onto the samples by chemical vapor deposition. Elemental analyses show differences in the impurity content and distribution which may be responsible for the electrical conductivity increase.

Mitigation of MHD phenomena in DCLL blankets by Flow Channel Inserts based on a SiC-sandwich material concept

The DCLL blanket is an attractive concept for future fusion reactors. In order to mitigate MHD effects from the interaction between flowing PbLi and magnetic field, Flow Channel Inserts (FCIs) need to be developed. SiC-based materials are main candidates for high-temperature FCIs. In this work, the MHD interactions and their possible mitigation by FCIs consisting of a porous SiC core with a dense protective SiC coating are studied. The dependency between MHD effects and the FCIs’ properties is discussed under relevant conditions for the DCLL concept. The results show that with a porous-dense SiC-sandwich material, a pressure gradient of ∼120 Pa/m is predicted for a 4 T magnetic field, and of ∼300 Pa/m for 10 T, if an FCI with insulating porous core (< ∼1 S/m) is used. Relevant cases considering a PbLi infiltration in the porous SiC core due to possible damages in the protective coating are presented.

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.

A simplified lithium vapor box divertor

A detached divertor plasma is predicted to be necessary to mitigate the heat fluxes and ion energy, and so sputtering, at the divertor plate of a fusion power plant. It has proven difficult in current experiments, however, to prevent the detachment front, once formed, from running up to the main plasma resulting in deterioration of pedestal performance. The lithium vapor box divertor localizes a dense cloud of lithium vapor away from the main plasma, in order to induce detachment at a stable, distant location. The vapor localization is created by local evaporation and nearby condensation, a configuration inaccessible for non-condensing seed impurities. This paper provides simulations of lithium vapor flow using the SPARTA direct simulation Monte Carlo (DSMC) code, in which the lithium vapor dynamics are governed by Li–Li collisions that should dominate in regions with little plasma. Inertia is included in this code, permitting the formation of shocks. The plasma model implemented in SPARTA is based on UEDGE results for the location of ionization and recombination. We find that a simplified lithium vapor box configuration, without baffles, provides robust stabilization of the detachment front and acceptable lithium vapor flow to the main chamber. Lithium is evaporated from a capillary porous surface on the private-flux side of the divertor, distant from the main plasma, and is condensed on the other side walls of the divertor chamber. The condensed lithium flows back to the evaporator through 2 cm internal diameter pipes. The capillary pressure differential at the surface of the evaporator is capable of overcoming MHD back-force in the piping, with a great deal of margin if a sandwich flow channel insert is implemented. Very little lithium should be accumulated on the first wall of the main chamber if it is maintained at 600 °C, as expected for a power-producing fusion system.

Impacts of geometrical characteristics on MHD flow and mechanical behaviors of FCI in blanket modules

Flow channel insert (FCI) serves as thermal and electrical insulator in the blanket module in the international thermonuclear experimental reactor (ITER). The geometrical characteristics of FCI greatly affect magneto-hydrodynamics (MHD) features, heat transfer and structural safety of the system. In this paper, the MHD flow and heat transfer in blanket modules with different FCI thicknesses and gap widths are investigated. Finite element method and finite volume method with a consistent and conservative scheme are used to deal with the magneto-thermo-fluid-mechanical fields. The detailed flow behaviors of metal fluid, thermal and mechanical behaviors in coupled field are investigated. A dimensionless parameter is introduced to evaluate the heat transfer efficiency. Results indicate the complicated effects of FCI thickness and gap width on heat transfer efficiency, pressure drop, first wall temperature and FCI thermal stress. The nonlinear and non-monotonous influences of geometrical characteristics on structural behavior and heat transfer efficiency are presented. The correlation between pressure drops and gap width is presented. After detailed analysis, a most promising design is recommended by evaluating heat transfer efficiency, fluid pressure drop, first wall temperature and structural stress. This work can be regarded as a foundation of future design and optimization of blanket modules.