Dual Coolant Lead Lithium Blanket 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.

FERMI: Fusion Energy Reactor Models Integrator

The Fusion Energy Reactor Models Integrator (FERMI) is an integrated simulation environment under development for the coupled simulation of the plasma, first wall, and blanket of fusion reactor designs. The FERMI goals are to shorten the overall design cycle while guaranteeing unprecedented accuracy, thus integrating fusion design activities, facilitating an optimal reactor design, and reducing development risks. These goals are achieved by coupling single-physics solvers into a multiphysics simulation environment (FERMI). The Integrated Plasma Simulator (IPS)–FASt TRANsport (IPS-FASTRAN) simulation framework is used for the following: plasma physics, MCNP/Shift codes for neutron and photon transport, OpenFoam for computational fluid dynamics and magnetohydrodynamics (MHD), HyPerComp Incompressible MHD solver for Arbitrary Geometry (HIMAG) for dual-coolant lead-lithium (DCLL) blankets, and DIABLO for structural mechanics simulations. These codes are coupled using the open-source library named precise Code Interaction Coupling Environment (preCICE). FERMI’s features are tested with the analysis of the liquid immersion blanket (LIB) [proposed in the Affordable Robust Compact (ARC)–class tokamak design], the DCLL blanket [proposed in the Fusion Pilot Plant (FPP) design], and other benchmark cases. The calculated figures of merit are the tritium breeding ratio, material activation, displacements per atom, shutdown dose rate, heat deposited in the vacuum vessel and blanket, temperature hot spots, and displacements caused by swelling and creep. A critical technical problem is multiphysics code coupling, which is tackled here, and the first three-dimensional (3D) simulations of the DCLL-FPP and LIB-ARC blankets are presented. To the authors’ knowledge, FERMI represents the first effort to perform 3D simulations of nuclear fusion first wall and blankets in a fully coupled multiphysics manner.

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.

Modeling of Transport Processes in Liquid-Metal Fusion Blankets: Past, Present, and Future

The successful development of robust breeding blanket systems will strongly rely on computational tools for predicting the complex behavior of the electrically conducting liquid-metal (LM) breeder flowing in the complex-shaped blanket ducts in the presence of a strong plasma-confining magnetic field, volumetric heating, and tritium generation. Associated transport processes involve magnetohydrodynamic (MHD) flows, heat transfer, corrosion, and tritium transport. This paper is an overview of past and present efforts in the development, application, and verification and validation (V&V) of such computational tools. As a result of the ongoing campaign on V&V of computer codes for LM blankets, the international fusion community has identified several candidates that promise to become real blanket design and analysis tools in the near future. Among them are HIMAG, MHD-UCAS, COMSOL Multiphysics, ANSYS FLUENT, ANSYS CFX, and OpenFOAM. The progress, over the last decade, in the application of such codes in blanket studies is tremendous. This is illustrated with two examples for a dual-coolant lead-lithium (DCLL) blanket: (1) integrated computer modeling for the recently designed DCLL blanket in the United States and (2) application of the code MHD-UCAS to the analysis of PbLi flows and heat transfer in a generic DCLL blanket prototype at high Hartmann (Ha ~ 104) and Grashof numbers (Gr ~ 1012). This paper also presents an approach to the development of a new integrated computational tool called the virtual dual-coolant lead-lithium (VDCLL) blanket, which elaborates the existing U.S. MHD code HIMAG.

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.

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.

Three-dimensional magneto convective flows in geometries relevant for DCLL blankets

Abstract The dual coolant lead lithium (DCLL) blanket is one of the liquid metal blanket concepts investigated within the framework of the EUROfusion Consortium. In the proposed design, the liquid metal serves as tritium breeder, neutron multiplier, and as coolant for the breeding zone. Magnetohydrodynamic (MHD) effects resulting from the interaction of the moving liquid metal with the magnetic field that confines the fusion plasma are coupled with thermal phenomena. Induced electromagnetic forces lead to significant modifications of the hydrodynamic flow and affect in turn heat and mass transfer. The presence of a high-intensity neutron flux in the liquid metal yields volumetric heating and associated buoyant forces that drive complex flow patterns in the blanket. The resulting convective motions cause strong thermal mixing, and an increment in the effective heat transfer coefficient that may increase heat losses from the liquid metal into the helium coolant. This could deteriorate the thermal efficiency of the blanket. Buoyant MHD phenomena may also result in reversed flow and closed recirculations where tritium accumulates and temperature locally increases. The aim of the present investigation is to address by means of 3D numerical simulations the main features of magneto-convective flows in a geometry typical for DCLL blankets, in which PbLi moves upwards in a poloidal duct that faces the first wall and, after making a U-turn, flows downwards at the back of the blanket module. The liquid metal enters and leaves the model geometry by flowing radially in rectangular channels. It is found that in the front duct the velocity is characterized by jets in the boundary layers along walls parallel to the magnetic field, as expected in case of electrically conducting ducts. In the rear channel, along the wall that separates the two poloidal ducts, a downward flow occurs with much higher velocities than in the rest of the channel. The influence of the magnetic field on these flow features is investigated.

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.

Heat transfer performance for DCLL blanket with no-wetting insulator walls

ABSTRACT Magnetohydrodynamic (MHD) effect and heat transfer are two key issues for design of dual coolant lead lithium (DCLL) blanket. Flow channel insert (FCI) has been applied to decouple the liquid metal from the walls to efficiently decline MHD pressure drops and reduce heat losses from the liquid metal for increasing bulk exit temperatures of the blanket. However, there are still big pressure drops and a higher velocity jet located at the gap flow. Moreover, the FCI made from silicon carbide (SiC) constitutes a complex blanket structures which potentially causes special flow phenomena. In the present work, the characteristics of fluid flow and heat transfer in the DCLL blanket channel are investigated for the first wall (FW) sprayed a layer of no-wetting nano coating (NWNC) on its inner surface. The results show that the pressure drop with NWNC wall is one-order magnitude lower than that with FCI in the general DCLL blanket. The Nusselt number on the NWNC wall is about half of that on the general wall. On this basis, a heat transfer criterion equation of DCLL channel is achieved for the NWNC wall without FCI. The results are compared with that criterion equation of general wall conditions, which indicates the criterion equation can well predict the convection heat transfer of DCLL channel.

Characterization and thermomechanical assessment of a SiC-sandwich material for Flow Channel Inserts in DCLL blankets

Flow Channel Inserts (FCIs) are key elements in the high-temperature Dual Coolant Lead Lithium (DCLL) blanket, since they insulate electrically the flowing PbLi to avoid MHD effects and protect the steel structure from the hot liquid metal. SiC-based materials are main candidates for high-temperature FCIs, being a dense-porous SiC-based sandwich material an attractive option. The present work is focused on the development of such a SiC-based material.On the one hand, in order to assess the suitability of the concept for FCIs, the main results of a stress analysis, MHD and heat transfer simulations are summarized. On the other hand, the experimental production of the SiC-based material is addressed, where the porous SiC core is manufactured from SiC powder by two different techniques: uniaxial pressing and gelcasting. The porosity is introduced using graphite spherical powder as a sacrificial template. After the production of the porous SiC core, a dense SiC coating of ˜200 μm thickness is deposited by Chemical Vapor Deposition (CVD); the coated material was tested against hot PbLi in corrosion experiments. The properties of the material in terms of thermal and electrical conductivities, flexural strength and elastic modulus were measured, with promising results for high-temperature FCIs.

Effects of magnetohydrodynamic mixed convection on fluid flow and structural stresses in the DCLL blanket

In this study, numerical simulations are conducted to investigate magnetohydrodynamic (MHD) mixed convection for buoyancy-assisted flows under strong magnetic field and large volumetric heat sources in the Dual-Coolant Lead-Lithium (DCLL) blanket. A magnetic-convection code based on the finite volume method is developed and validated using benchmark solutions. A consistent and conservative scheme is applied to deal with the electric current conservation issues. The PISO algorithm on unstructured collocated meshes is employed to solve the N-S equations considering the Lorentz force effect. Deformations and stresses of flow channel insert (FCI) are analyzed using the finite element method (FEM). Cases with high Hartmann number of 9600–19,200, high Reynold number of 31,000 and high Grashof number of 3.5×1011 are used in the numerical simulations. The buoyancy effects as well as electric conductivity of the FCI on poloidal flows in rectangular channel with a SiC FCI are analyzed, considering non-uniform exponential volumetric heat source and toroidal magnetic field. The deformation field and stress field of the FCI are calculated under MHD mixed convection effects. Results demonstrate that a reverse flow occurs near the cold wall in the bulk region, which is a special phenomenon resulted from buoyancy. Compared to MHD forced convection, buoyancy delivers enhanced temperature uniformity, a drastically changed velocity distribution, and a slightly elevated pressure drop. At the same time, the pressure drop between inlet and outlet has a linear relation with eB/5. Mixed convection temperatures is insensitive to FCI electrical conductivity, and only velocity near the cold wall appears sensitive. In the FCI, both magnetic field and electrical conductivity positively correlate with thermal stresses. Simulations also suggest the buoyancy effect reduces temperature difference across FCI and thermal stress.

Numerical simulations of 3D magnetohydrodynamic flows in dual-coolant lead lithium blankets

In the dual coolant lead lithium blanket (DCLL) the liquid metal PbLi is used as coolant to remove the volumetrically generated heat. This requires higher flow velocities than in separately cooled blanket concepts, where the liquid metal serves exclusively as breeder, neutron multiplier and shield against high neutron radiation. The relatively fast movement of the electrically conducting fluid in the strong magnetic field confining the fusion plasma induces electric currents, which are responsible for strong Lorentz forces, high magnetohydrodynamic (MHD) pressure drop, and substantial modifications of velocity profiles compared with hydrodynamic flows. In order to support the design activities of a DCLL blanket, 3D numerical MHD simulations for one column of such a blanket module have been performed. The simulations take into account, that currents may close along the inner conducting sheet of sandwich-type flow channel inserts that are foreseen for pressure drop reduction. The applied numerical code has been carefully validated. It applies for magnetic fields of arbitrary orientation and is capable of simulating the liquid metal MHD flow in the blanket in the parameter range relevant for fusion applications.

Numerical model of dual-coolant lead–lithium (DCLL) blanket

The analysis of Dual-Coolant Lead–Lithium (DCLL) blankets requires application of Computational Fluid Dynamics (CFD) methods for electrically conductive liquids in geometrically complex regions and in the presence of a strong magnetic field. Together with a Magneto Hydro Dynamics (MHD) capability, the general purpose CFD is applicable or modeling of DCLL blankets. This presentation describes a numerical model based on the customized general purpose CFD code CFX from ANSYS. The model involves simultaneous modelling of two different liquids in different regions: helium coolant, and lead lithium eutectic. Additionally neutron heating is included in the code using three dimensional heat source distribution mapped from the results of the Attila simulations. Surface heating of the front face of the blanket is also included. Geometry of the sample blanket is introduced directly from the CAD using step file. Most of the meshing was performed automatically using CFX mesher. Special grid generation methods were used to insure accurate resolution of the near wall boundary layers including several layers of large aspect ratio prismatic elements. DCLL design also includes some narrow flow regions between SiC insert and structure. These regions were meshed using sweep method to avoid high aspect ratio tetrahedral elements. The numerical model was tested against benchmarks specifically selected for liquid metal blanket applications, such as straight rectangular duct flows with Hartmann number of up to 15,000. Results for a general three dimensional case of the DCLL blanket are also included.

Magnetohydrodynamic and thermal analysis of PbLi flows in poloidal channels with flow channel insert for the EU-DCLL blanket

Magnetohydrodynamic (MHD) processes are known to be critically important for the dual coolant lithium lead (DCLL) breeding blanket (BB) concept. In order to minimize the MHD pressure drop in the European DCLL blanket design, the liquid metal breeder (PbLi) is decoupled electrically from the ferritic–martensitic structure (EUROFER) using insulating ceramic-based flow channel inserts (FCIs). The impact of the FCI on the velocity profile and the pressure drop in the DCLL front poloidal channels is studied. Two-dimensional momentum and induction equations for fully developed flows are solved numerically using the ANSYS-Fluent simulation platform under DCLL-relevant conditions (, ). Velocity and pressure drop in the PbLi flows have been computed first for a channel without FCI and then for three possible alumina-based FCI design: two types of sandwich FCI and one naked FCI. In order to analyze thermal effects in the blanket, the obtained velocity profiles are used as inputs to solve the 3D energy equation. The computations of the temperature distribution in the DCLL poloidal front channel with a prototypical exponentially varying heat generation profile are obtained using convective boundary conditions. Results show the effect of the FCI and MHD phenomena on heat transfer.

Sizing of a recuperative supercritical CO2 Brayton cycle as power conversion system for DEMO fusion reactor based on Dual Coolant Lithium Lead blanket

A modified recuperative supercritical CO2 cycle for DEMO fusion reactor is analysed. A layout with just one recuperator is used, because of the relatively low temperature of the breeding blanket coolants. The proposed cycle is able to integrate several thermal sources with different temperature ranges and includes two kinds of thermal energy storage to overcome the pulse operation: a two-tank molten salt storage and a concrete storage. The design point is obtained using the Engineering Equation Solver (EES) environment, which allows to use pure substance models for CO2, helium and water. Once the design point is calculated, the sizing of pipes, heat exchangers, turbomachines and energy storage systems has been performed in order to obtain a preliminary estimation of the layout and its complexity. So, the power conversion system has been split into four equal parts in order to use commercial pipe diameters. Even though Printed Circuit Heat Exchangers (PCHE) have been used, extremely large sizes have been obtained, especially for the HTR recuperator. These sizes contrast with the small values obtained for the turbomachines, whose preliminary design has been carried out, using the AXIAL™ meanline design software. In addition, the two largest heat exchangers are divided into serial and parallel configurations when assessing the allocation of the components of the power conversion system to reduce the footprint. An average electric efficiency (including pulse and dwell period) of 28.25% has been reached. The required mass of molten salt per each power conversion subsystem is 2568 t, while the mass of concrete is 833 t. Regarding the footprint, 85 × 170 m2 are required for each power conversion subsystem, including the storage systems.

Development, Characterization, and Testing of a SiC-Based Material for Flow Channel Inserts in High-Temperature DCLL Blankets

Flow channel inserts (FCIs) are the key elements in the high-temperature dual-coolant lead-lithium blanket, since in this concept the flowing PbLi reaches temperatures near 700 °C and FCIs should provide the necessary thermal and electrical insulations to assure a safe blanket performance. In this paper, the use of a SiC-sandwich material for FCIs consisting of a porous SiC core covered by a dense chemical vapor deposition-SiC layer is studied. A fabrication procedure for porous SiC is proposed and the resulting materials are characterized in terms of thermal and electrical conductivities (the latter before and after being subjected to ionizing radiation) and flexural strength. SiC materials with a wide range of porosities are produced; in addition, preliminary results using an alternative route based on the gel-casting technique are also presented, including the fabrication of hollow samples to be part of future lab-scale FCI prototypes. Finally, to study the corrosion resistance of the material in hot PbLi, corrosion tests under static PbLi at 700 °C and under flowing PbLi at ~10 cm/s and 550 °C, with and without a 1.8–2T magnetic field, were performed to materials coated with a 200–400- $\mu \text{m}$ -thick dense SiC layer, obtaining promising results.

Pressure drop and velocity changes in MHD pipe flows due to a local interruption of the insulation

In liquid metal blanket concepts, such as the dual coolant lead lithium (DCLL) blanket, in which the PbLi serves to cool the breeding zone, the liquid metal has to flow with sufficiently large velocity to guarantee a suitable removal of the volumetric heat generated in the fluid. Large velocities lead to a high pressure drop caused by magnetohydrodynamic (MHD) interactions of the liquid metal with the plasma confining magnetic field. In order to reduce MHD pressure losses in DCLL blankets, it is foreseen to decouple electrically the PbLi from the conducting wall of the ducts. This can be achieved by inserting insulating layers inside pipes and channels. In this paper we investigate MHD flows in well-conducting pipes with flow channel inserts (FCI). The influence on the pressure drop of the finite electric conductance of the layer and of the presence of an interruption in the insulation is analyzed. Numerical results show that under realistic operating conditions, i.e. for sufficiently small electric conductance of the insert and large magnetic fields, the ensuing additional MHD pressure losses are still acceptable. However, the discontinuity of the insulation causes significant modifications of the velocity distribution in the pipe, which have to be taken into account, since they can affect heat and mass transfer phenomena.