Magnetohydrodynamic Pressure Drop Research Articles

RELAP5/Mod3.3 MHD module development and validation: WCLL-TBM mock-up model

Magnetohydrodynamic (MHD) phenomena significantly impact the design of magnetic-confinement fusion reactors, particularly in the context of breeding blankets (BB) utilizing liquid metals (LMs) as working fluids. These effects arise from the interaction between the electro-conductive flowing metal and the magnetic field used for plasma confinement in the reactor chamber. Induced electrical currents in the liquid generate Lorentz forces, thereby altering flow behaviour in comparison to standard hydrodynamic conditions. For example, MHD effects modify velocity distribution and mass transport within ducts, amplify pressure losses, and influence heat transfer mechanisms. Accurate estimation of these impacts is crucial for the effective design of a liquid metal breeding blanket. While computational tools are essential for fusion-related physical analyses, no comprehensive MHD code currently exists for simulating all relevant phenomena in a liquid metal blanket. In this context, models predicting both distributed and concentrated MHD pressure drops have been integrated into the thermal-hydraulic system code RELAP5/Mod3.3. The Verification and Validation (V&V) process compares code results to direct numerical simulations and experimental data. For validation, RELAP5 recreates experimental results of a Water Cooled Lithium Lead test blanket module at magnetic field intensities ranging from Ha=500−3000, confirming the reliability of the newly implemented MHD subroutines for predicting pressure drops within this parameter range.

Challenges towards an acceleration in stellarator reactors engineering: The dual coolant lithium–lead breeding blanket helical-axis advanced stellarator case

Under the ambitious EUROfusion mission of “bringing the stellarator line to technological maturity”, the development of a Dual Coolant Lithium–Lead (DCLL) Breeding Blanket (BB) for a Helical-Axis Advanced Stellarator (HELIAS) started. The BB is the crucial systems to achieve tritium self-sufficiency in fusion power plants. The DCLL has potentialities to answer the challenges posed by complex HELIAS configuration, having liquid breeder and decoupled first wall (FW) and breeding zone circuits. Both characteristics are being empowered to simplify remote maintenance and integration of the BB segments. Hence, a “quasi-toroidal” BB segmentation has been proposed to minimize the magnetohydrodynamic pressure drop eschewing complex electrical insulating components while hindering maintenance. Such controversy motivated the use of a detached FW small panels manageable through ports. On this basis, a decoupled Capillary Porous System FW has been assessed under thermal-hydraulics and neutronics point of view. Moreover, ad-hoc tools have been developed for the parametrization of models and convergence toward a viable DCLL HELIAS design, speeding-up the coupling of computer-aided design modelling and analyses. Such novel strategies are described in view of a potential acceleration of the stellarator reactor engineering and by providing an overview of the stellarator challenges inside a global context.

Optimization studies for a manifold of a liquid metal blanket of a fusion reactor

Magnetohydrodynamic (MHD) flows in a manifold of a liquid metal blanket can significantly contribute to the blanket pressure drop, which is a feasibility issue for almost all liquid metal blanket concepts. Here, optimization studies for a prototypic inlet manifold that feature flow expansion are performed for three expansion angles, θ = 45°, 60° and 75°, expansion ratio of 4, and a wide range of Hartmann (Ha) and Reynolds () numbers: 1000<Ha<10,000, and 50<Re<10,000 aiming at the MHD pressure drop reduction and a more uniform flow distribution at the exit of the manifold. The 150 flow cases computed with COMSOL Multiphysics in 3D provide an extended database for the pressure drop coefficient, which was used to construct a correlation for the 3D MHD pressure drop. In addition, many data analyzes were performed to characterize the flow inside the manifold and access the most important flow characteristics, such as the recirculation flow bubble that appears when the liquid metal enters the expansion region and the flow development length as a function of Ha,Re and θ.

A simple MHD model for coupling poloidal manifolds to breeder units in liquid metal blankets

An efficient hybrid model has been developed for prediction of magnetohydrodynamic pressure drop in electrically couple manifolds of liquid metal blankets and flow partitioning in breeder units. The tool combines global mass conservation and pressure drop correlations with detailed 3D simulations. When applied to a TBM-like geometry, the model reveals strong electromagnetic coupling with increased flow in BUs is near both ends of the module, while weak coupling with almost no flow is found in BUs in the middle of the module. The method is very efficient and it applies for a large number of BUs as foreseen in a DEMO design. It will be applied in future to determine the optimum position of the baffle plates in manifolds that guarantees uniform flow partitioning in all breeder units.

A magneto-hydrodynamic analysis of liquid metal flows in the conducting and insulating wall ducts using a finite element tool

In various fusion reactors, a liquid conducting metal has been considered an ideal breeder and a coolant. The magneto-hydrodynamic (MHD) analysis of liquid metal flow in a typical square duct plays a major role in designing reactor components. Conducting fluid flow induces an eddy current in a magnetic field, which, produces electromagnetic force leading to high MHD pressure drop. The electrical conductivity of the walls substantially affects the number of liquid metal flows and forces produced due to eddy current, producing severe pressure drop in it. To reduce the effect of eddy current and MHD pressure drop, the time-varying electromagnetic FE analysis has been carried out for electromagnetic forces and computational fluid dynamic analysis in the coupled field environment with conducting wall ducts and with insulated walls. FEA results are compared with analytically calculated parameters and validated.

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.

Electrical insulation performances of ceramic materials developed for advanced blanket systems under intense radiations

Various oxides and SiC have been proposed as candidate materials for electrical insulation coatings and inserts to suppress the magnetohydrodynamic (MHD) pressure drop in liquid metal fusion blanket systems. From the early stage of the MHD insulator development, the magnitudes of the radiation-induced conductivities (RICs), i.e., increases in conductivities by radiation excitation, have been evaluated on bulk and coated specimens by using several radiation sources. While the insulating performances of the oxide coated and SiC plate specimens are inferior to those of high quality and purity bulk materials due to cracks, pits, sintering additives, etc., the results indicate that the RIC phenomenon would not prevent the MHD insulators from achieving the required performances (10−3–10−2 S/m for coatings, 102 S/m for inserts) at the first wall of the blanket (500–700 °C, several kGy/s). The recent design investigation of blanket modules for DEMO reactor conditions provides more precise information for prediction of the performances in reactors and conditions to be simulated in the future irradiation damage studies. In the case of the coatings, the suppression of recoiled Li from the liquid metal breeder/coolant might be an issue to be considered in the development.

Demonstration of RELAP5-3D for transient analysis of a dual coolant lead lithium fusion blanket concept

Our research aims to build a multiphysics framework for transient analysis of the Dual-Coolant Lead-Lithium (DCLL) blanket design of the proposed Fusion Nuclear Science Facility (FNSF) for all Anticipated Operational Occurrences (AOOs) using Reduced Order Models (ROMs). This paper presents an assessment of using RELAP5-3D for transient thermal-hydraulic blanket analysis of the DCLL design. Preliminary validation studies for the RELAP5-3D properties were conducted using a representative vertical flow loop model and a comparison study using experimental data from thermal convection corrosion loops at ORNL. These studies inspected the thermal hydraulic response of Lead-Lithium Eutectic (PbLi) systems within the RELAP5-3D code; mainly pressure drop and heat transfer, as compared to analytical calculations and experimental data. The Magnetohydrodynamic (MHD) pressure drop effect for liquid metal under the effects of a uniform magnetic field was implemented into our models using an equivalent forms loss coefficient based on the phasic momentum equations. We verified our implementation of MHD pressure drop within RELAP5-3D using a systematic approach consisting of two studies. Models were developed to perform comparison studies using experimental data from the Argonne Liquid metal EXperiment (ALEX) facility and the Magnetohydrodynamic PbLi Experiment (MaPLE) facility. Using the developed validation basis, we built a simplified DCLL channel model within RELAP5-3D, inspected MHD pressure drop and performed transient temperature analysis. The DCLL channel model used radial heating data from the International Thermonuclear Experimental Reactor (ITER) which was normalized to the FNSF design. A representative startup transient was performed using a relative power curve based on current PWR power ramp limits. This study demonstrated that RELAP5-3D ROMs are capable of accurate transient analysis of the DCLL blanket. We have since utilized MCNP to develop heating profiles based on the FNSF design and are working toward implementing them into our DCLL model.

Preliminary MHD pressure drop analysis for the prototypical WCLL TBM with RELAP5/MOD3.3

In fusion reactor development, the design of the breeding blanket (BB) represents an important technical challenge due to the extreme operative conditions that the component must withstand. One of the critical issues of a liquid metal BB is the occurring of magnetohydrodynamic (MHD) effects within the piping network that transports the electro-conductive fluid. Predicting MHD phenomena is fundamental for a reliable and efficient blanket design and computational tools are indispensable to achieve a fusion-relevant physical analysis. For this reason, a dedicated MHD module for the System Thermal-Hydraulic (STH) code RELAP5/MOD3.3 (RELAP5) is under development at Sapienza University of Rome. In its current state, RELAP5 can evaluate MHD pressure losses in many common layouts for BB piping system. In a previous work of the Authors, the verification and validation (V&V) procedure of the MHD module has been discussed. In this paper, the code is used to assess the MHD pressure loss in the Water-Cooled Lithium Lead Test Blanket Module (TBM). Furthermore, the geometry of the TBM box is optimized to reduce the MHD pressure loss and to equalize the flow distribution among the Breeding Units.

Toward full simulations for a liquid metal blanket: part 2. Computations of MHD flows with volumetric heating for a PbLi blanket prototype at Ha ∼ 104 and Gr ∼ 1012

On the pathway toward full simulations for a liquid metal (LM) blanket, this part 2 extends a previous study of purely magnetohydrodynamic (MHD) flows in a DCLL blanket in reference Chen et al (2020 Nucl. Fusion 60 076003) to more general conditions when the MHD flow is coupled with heat transfer. The simulated prototypic blanket module includes all components of a real LM blanket system, such as supply ducts, inlet and outlet manifolds, multiple poloidal ducts and a U-turn zone. Volumetric heating generated by fusion neutrons is added to simulate thermal effects in the flowing lead–lithium (PbLi) breeder. The MHD flow equations and the energy equation are solved with a DNS-type finite-volume code ‘MHD-UCAS’ on a very fine mesh of 470 × 106 cells. The applied magnetic field is 5 T (Hartmann number Ha ∼ 104), the PbLi velocity in the poloidal ducts is 10 cm s−1 (Reynolds number Re ∼ 105), whereas the maximum volumetric heating is 30 MW m−3 (Grashof number Gr ∼ 1012). Four cases have been simulated, including forced- and mixed-convection flows, and either an electrically conducting or insulating blanket structure. Various comparisons are made between the four computed cases and also against the purely MHD flows computed earlier in reference Chen et al (2020 Nucl. Fusion 60 076003) with regards to the (1) MHD pressure drop, (2) flow balancing, (3) temperature field, (4) flows in particular blanket components, and (5) 3D and turbulent flow effects. The strongest buoyancy effects were found in the poloidal ducts. In the electrically non-conducting blanket, the buoyancy forces lead to significant modifications of the flow structure, such as formation of reverse flows, whereas their effect on the MHD pressure drop is relatively small. In the electrically conducting blanket case, the buoyancy effects on the flow and MHD pressure drop are almost negligible.

Experimental investigations on electrical-insulation performance of Al2O3 coatings for high temperature PbLi liquid metal applications

Electrical-insulating coatings are of great importance for applications in liquid metal breeder/coolant based systems relevant to nuclear fusion power plants. In specific to lead–lithium eutectic (Pb-16Li), a candidate breeder material, such coatings are being actively investigated worldwide for their criticality in addressing various functionalities including, but not limited to, reduction in Magneto-Hydro Dynamics (MHD) pressure drop, corrosion resistance to structural materials and development of specific diagnostics, like two-phase detection techniques. For such applications, a candidate coating must be demonstrated for its compatibility with corrosive media, endurance towards high operational temperatures and integrity of electrical-insulation over long operational durations without substantial degradation. Further, quantitative performance assessment of coated substrates within PbLi environment over long operational durations is rendered difficult due to scarcity of relevant in-situ insulation resistance data. To address this shortfall, a preliminary experimental study was performed at Institute for Plasma research (IPR) towards application of AlPO4 bonded high-purity alumina (Al2O3) coatings on SS-316L substrates and further rigorous validation in static PbLi environment. The adopted coating process required a low temperature heat treatment (<430 °C) and could yield average coating thicknesses in the range of ∼ 100 µm – 500 µm. Coated samples were validated for their electrical-insulation integrity in static PbLi over two test campaigns for continuous durations of over 700 h and 1360 h, including thermal cycling, at operational temperature in the range of 300 °C-400 °C. Volumetric electrical-resistivity, estimated through high-voltage insulation resistance measurements at relevant temperatures, remained of the order of 109-1011 Ω-cm without significant degradation. In-situ estimations of thermal derating factors establish good electrical-insulation characteristics after long term exposure to liquid PbLi. This paper presents details of utilized coating application methods, coating thickness estimations, liquid metal test set-up, insulation performance and critical observations from SEM/EDX and XRD analysis on the tested samples.

Numerical calculations on liquid-metal magnetohydrodynamic flow in rectangular channel with wavelike uneven walls

Numerical calculations have been performed on liquid-metal magnetohydrodynamic (MHD) flows in rectangular channels with wavelike uneven walls in order to propose a flow channel in which the MHD pressure drop decreases. The calculations have been carried out for a Hartmann number of 10,000, a wall conductance ratio of 0.05, and channel aspect ratios of 1/4 and 1/9, in order to simulate typical conditions proposed to fusion reactor blankets. In the range examined in the present calculations, the Poiseuille number, which is the product of pressure gradient and Reynolds number, decreases to about half at maximum of that in a corresponding base case, i.e. a rectangular channel with flat walls.

Development of a RELAP5/MOD3.3 Module for MHD Pressure Drop Analysis in Liquid Metals Loops: Verification and Validation

Magnetohydrodynamic (MHD) phenomena, due to the interaction between a magnetic field and a moving electro-conductive fluid, are crucial for the design of magnetic-confinement fusion reactors and, specifically, for the design of the breeding blanket concepts that adopt liquid metals (LMs) as working fluids. Computational tools are employed to lead fusion-relevant physical analysis, but a dedicated MHD code able to simulate all the phenomena involved in a blanket is still not available and there is a dearth of systems code featuring MHD modelling capabilities. In this paper, models to predict both 2D and 3D MHD pressure drop, derived by experimental and numerical works, have been implemented in the thermal-hydraulic system code RELAP5/MOD3.3 (RELAP5). The verification and validation procedure of the MHD module involves the comparison of the results obtained by the code with those of direct numerical simulation tools and data obtained by experimental works. As relevant examples, RELAP5 is used to recreate the results obtained by the analysis of two test blanket modules: Lithium Lead Ceramic Breeder and Helium-Cooled Lithium Lead. The novel MHD subroutines are proven reliable in the prediction of the pressure drop for both simple and complex geometries related to LM circuits at high magnetic field intensity (error range ±10%).

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.

Status and Progress of Liquid Metal Thermofluids Modeling for the U.S. Fusion Nuclear Science Facility

At present, the U.S. Fusion Engineering Systems Study (FESS) considers several cooling/breeding concepts that utilize flowing liquid metals (LMs), Li, or eutectic PbLi alloy as working fluids for implementation of these concepts in the Fusion Nuclear Science Facility (FNSF). In this paper, we review recent modeling activities aimed at the investigation of LM flows and heat transfer relevant to the FESS-FNSF program. In particular, considerations are given to (1) development and validation & verification of computational magnetohydrodynamic (MHD) codes, (2) characterization of critical coupled MHD/heat transfer phenomena, and (3) design and analysis for selected LM applications in the FNSF. Under these three research thrusts, the reviewed topics including the MHD code HyPerComp Incompressible MHD solver for Arbitrary Geometries (HIMAG), MHD mixed-convection flows, MHD pressure drop in the blanket inlet/outlet manifolds, PbLi flows in a thermal convection loop, MHD PbLi flows in a dual-coolant lead-lithium blanket prototype, and a design window for a flowing Li divertor with He-cooled substrate.

Influences of the bend angle and the locally different electrical conductivity of the structural walls on the flow characteristics of the LM MHD splitting flows

The minimization of the magnetohydrodynamic (MHD) pressure drop is a hot issue in the design of liquid-metal blanket. The current study aims to investigate the flow distribution and MHD pressure drop in a 3-D magnetohydrodynamic (MHD) flow of a liquid-metal (LM) through a conduit with one inlet and two outlet ducts. CFX software is used to investigate the features of the MHD splitting flows. Here, cases with various electrical conductivity of the structural walls in the two outlet ducts are analyzed with the consideration of different bend angles, which yields various flow distributions in different cases, and also causes mass imbalance in the two outlet ducts. The results show that, when the bend angle is fixed, the mass imbalance increases with the growing discrepancy of the electrical conductivity between the two outlet ducts. Meanwhile, the uneven mass flow rate therein also depends on the variation of the bend angle. Furthermore, this study found that locally different electrical conductivity of the structural walls in T-junction ducts can reduce the MHD pressure drop significantly, and 70% of the pressure drop is reduced within the Test Blanket Module (TBM) when the discrepancy in the electrical conductivity of the two outlet ducts is the largest.

Fabrication and characterization of ceramic-iron joint coating for electrical insulation

For the realization of liquid metal blanket systems, fabrication of a ceramic-metal multi-layer coating has been proposed to obtain both electrical insulation for the mitigation of magneto-hydrodynamic pressure drop and compatibility with liquid metals. The corrosion protection layer using a metal foil needs to be joined to the ceramic coating to ensure integrity in the flowing environment. Besides, the ceramic coating should be as thin as possible in terms of thermal conduction. In this study, we fabricated ceramic-iron joint coatings using iron foils and thin ceramic coatings by hot pressing. Three kinds of the ceramic coating with different crystallization states were used for joining to compare adhesion to the ceramic coating. The coating before and after joining fulfilled the requirements for electric insulation. The joint coating showed a sufficient adhesion strength to withstand the stress by liquid metal flow due to formation of an iron oxide layer between the iron foil and the ceramic coating. Although the thermal conductivity of the joint coating slightly decreased due to the heat resistance of the interface between the iron foil and the ceramic coating, the joint coating is a promising functional coating for liquid metal blanket systems.

Physical Background, Computations and Practical Issues of the Magnetohydrodynamic Pressure Drop in a Fusion Liquid Metal Blanket

In blankets of a fusion power reactor, liquid metal (LM) breeders, such as pure lithium or lead-lithium alloy, circulate in complex shape blanket conduits for power conversion and tritium breeding in the presence of a strong plasma-confining magnetic field. The interaction of the magnetic field with induced electric currents in the breeder results in various magnetohydrodynamic (MHD) effects on the flow. Of them, high MHD pressure losses in the LM breeder flows is one of the most important feasibility issues. To design new feasible LM breeding blankets or to improve the existing blanket concepts and designs, one needs to identify and characterize sources of high MHD pressure drop, to understand the underlying physics of MHD flows and to eventually define ways of mitigating high MHD pressure drop in the entire blanket and its sub-components. This article is a comprehensive review of earlier and recent studies of MHD pressure drop in LM blankets with a special focus on: (1) physics of LM MHD flows in typical blanket configurations, (2) development and testing of computational tools for LM MHD flows, (3) practical aspects associated with pumping of a conducting liquid breeder through a strong magnetic field, and (4) approaches to mitigation of the MHD pressure drop in a LM blanket.

Pressure drop in a prototypical 3D magnetohydrodynamic flow across contraction of a fusion blanket manifold

ABSTRACT Predicting 3D magnetohydrodynamic (MHD) pressure losses associated with liquid metal flows in complex geometry ducts is required to design breeding blankets for fusion reactors. Of such components, manifolds exhibit major pressure losses. Recent correlations [T. Rhodeset al. Magnetohydrodynamic pressure drop and flow balancing of liquid metal flow in a prototypic fusion blanket manifold. Phys. Fluids. 2018; 30: 057101.] demonstrate promise for predicting pressure drops in electrically insulated inlet manifolds. In the present work, the extend to which these correlations can be applied to outlet manifolds, which feature sudden contractions, is investigated in both viscous-electromagnetic (VE) and inertial-electromagnetic (IE) regimes for Reynolds numbers 50 < Re < 1500, Hartmann numbers 2500 < Ha < 5475, and expansion/contraction ratio 10. Numerical computations have shown that the MHD pressure drops in the eutectic lead-lithium (PbLi) flows in contractions are almost identical to those in the flows featuring expansion with slightly higher magnitudes in the contraction cases. The small discrepancy in the MHD pressure drop between contractions and expansions (<8%) suggests that the earlier obtained correlations for the 3D MHD pressure drop in a duct flow with a sudden expansion can also be applied to flows with a sudden contraction.

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.