The breeding blanket with integrated first wall (FW) is the key nuclear component for power extraction, tritium fuel sustainability, and radiation shielding in fusion reactors. The ITER device will ...address plasma burn physics and plasma support technology, but it does not have a breeding blanket. Current activities to develop “roadmaps” for realizing fusion power recognize the blanket/FW as one of the principal remaining challenges. Therefore, a central element of the current planning activities is focused on the question: what are the research and major facilities required to develop the blanket/FW to a level which enables the design, construction and successful operation of a fusion DEMO? The principal challenges in the development of the blanket/FW are: (1) the Fusion Nuclear Environment – a multiple-field environment (neutrons, heat/particle fluxes, magnetic field, etc.) with high magnitudes and steep gradients and transients; (2) Nuclear Heating in a large volume with sharp gradients – the nuclear heating drives most blanket phenomena, but accurate simulation of this nuclear heating can be done only in a DT-plasma based facility; and (3) Complex Configuration with blanket/first wall/divertor inside the vacuum vessel – the consequence is low fault tolerance and long repair/replacement time.
These blanket/FW development challenges result in critical consequences: (a) non-fusion facilities (laboratory experiments) need to be substantial to simulate multiple fields/multiple effects and must be accompanied by extensive modeling; (b) results from non-fusion facilities will be limited and will not fully resolve key technical issues. A DT-plasma based fusion nuclear science facility (FNSF) is required to perform “multiple effects” and “integrated” experiments in the fusion nuclear environment; and (c) the Reliability/Availability/Maintainability/Inspectability (RAMI) of fusion nuclear components is a major challenge and is one of the primary reasons why the blanket/FW will pace fusion development toward a DEMO.
This paper summarizes the top technical issues and elucidates the primary challenges in developing the blanket/first wall and identifies the key R&D needs in non-fusion and fusion facilities on the path to DEMO.
The DCLL is an attractive breeding blanket concept that leads to a high-temperature (T∼700°C), high thermal efficiency (η>40%) blanket system. The key element of the concept is a flow channel insert ...(FCI) that serves as an electrical and thermal insulator to reduce the magnetohydrodynamic (MHD) pressure drop and to decouple the temperature-limited RAFM (reduced-activation ferritic/martensitic) steel wall from the flowing hot PbLi. The paper introduces the concept, reviews history of the development of the DCLL in the US and worldwide and then identifies critical R&D needs prior to fusion environment testing in four research areas important to the successful development of the DCLL concept: (1) PbLi MHD thermofluids, (2) fluid materials interaction, (3) tritium transport, and (4) FCI development and characterization. For these areas, the most important R&D results obtained in the US in the ITER DCLL TBM program (2005–2011) and more recently are reviewed, including experimental and computational studies of MHD PbLi flows, corrosion of RAFM, tritium permeation, and silicon carbide FCI fabrication and material qualification. We also discuss required features of non-fusion facilities for DCLL blanket testing, where current lab experiments and modeling could progress to multiple effects and partially-integrated studies that approach as nearly as possible prototypic, integrated blanket conditions prior to testing in a fusion environment.
A consistent, conservative and accurate scheme has been designed to calculate the current density and the Lorentz force by solving the electrical potential equation for magnetohydrodynamics (MHD) at ...low magnetic Reynolds numbers and high Hartmann numbers on a finite-volume structured collocated grid. In this collocated grid, velocity (
u
), pressure (
p), and electrical potential (
φ) are located in the grid center, while current fluxes are located on the cell faces. The calculation of current fluxes on the cell faces is conducted using a conservative scheme, which is consistent with the discretization scheme for the solution of electrical potential Poisson equation. A conservative interpolation is used to get the current density at the cell center, which is used to conduct the calculation of Lorentz force at the cell center for momentum equations. We will show that both “conservative” and “consistent” are important properties of the scheme to get an accurate result for high Hartmann number MHD flows with a strongly non-uniform mesh employed to resolve the Hartmann layers and side layers of Hunt’s conductive walls and Shercliff’s insulated walls. A general second-order projection method has been developed for the incompressible Navier–Stokes equations with the Lorentz force included. This projection method can accurately balance the pressure term and the Lorentz force for a fully developed core flow. This method can also simplify the pressure boundary conditions for MHD flows.
A conservative formulation of the Lorentz force is given here for magnetohydrodynamic (MHD) flows at a low magnetic Reynolds number with the current density calculated based on Ohm’s law and the ...electrical potential formula. This conservative formula shows that the total momentum contributed from the Lorentz force is conservative when the applied magnetic field is constant. For the case with a non-constant applied magnetic field, the Lorentz force has been divided into two parts: a strong globally conservative part and a weak locally conservative part.
The conservative formula has been employed to develop a conservative scheme for the calculation of the Lorentz force on an unstructured collocated mesh. Only the current density fluxes on the cell faces, which are calculated using a consistent scheme with good conservation, are needed for the calculation of the Lorentz force. Meanwhile, a conservative interpolation technique is designed to get the current density at the cell center from the current density fluxes on the cell faces. This conservative interpolation can keep the current density at the cell center conservative, which can be used to calculate the Lorentz force at the cell center with good accuracy. The Lorentz force calculated from the conservative current at the cell center is equivalent to the Lorentz force from the conservative formula when the applied magnetic field is constant, which can conserve the total momentum. We will further prove that the simple interpolation scheme used in the Part I M.-J. Ni, R. Munipalli, N.B. Morley, P.Y. Huang, M. Abdou, A current density conservative scheme for MHD flows at a low magnetic Reynolds number. Part I. On a rectangular collocated grid system, Journal of Computational Physics, in press,
doi:10.1016/j.jcp.2007.07.025 of this series of papers is conservative on a rectangular grid and can keep the total momentum conservative in a rectangular grid.
Development of electrical insulation coatings, which insulate an induced electric current from electrical conducting walls, is a key technology for the research and development of self-cooled liquid ...metal blanket including lead–lithium (PbLi) fusion blankets. As for magnetohydrodynamic (MHD) thermofluid study, an electrical insulation coating is extremely important from the viewpoint of the secure electrical insulating wall condition. The present study employs a sol–gel (SG) method to fabricate an Al
2O
3 coating, and discusses the feasibility of the SG coating as an electrical insulation coating for the PbLi through the electrical insulation test in the molten PbLi pool and the SEM with EDS analysis on the SG coating structure. The present study shows that the SG coating will be a potential electrical insulation coating for PbLi with both the operation time and the temperature limitation.
The direct simulation of a droplet falling in a different background liquid is presented. The complete Navier–Stokes problem is solved using a projection method coupled with a level set method. A ...detailed analysis is given to show that reinitialization procedure of level set method M. Sussman, P. Smereka, S. Osher, Level set approach for computing solutions to incompressible two-phase flow, Journal of Computational Physics 114 (1) (1994) 146–159 cannot preserve the volume of a droplet. A variable time step method is presented to improve conservation. We study the effect of a wall on the droplet motion by settling a single circular droplet through a quiescent fluid at different lateral positions between parallel walls. The effect of inertial force on the deformation and oscillatory motion of a droplet is investigated by changing the Reynolds numbers. The deformation mechanism is studied for different Weber numbers. In addition, the interaction effect between droplets is studied by settling two and three droplets in the parallel channel. The Karman vortex distribution is shown to explain the oscillatory mechanism of droplet motion.
We summarize here the results of ongoing studies for magnetohydrodynamic (MHD) flows and heat transfer in the eutectic alloy lead–lithium (PbLi), which is used as a breeder and coolant, for three US ...Dual-Coolant Lead–Lithium (DCLL) blanket scenarios: ITER H-H, ITER D-T, and DEMO. The paper focuses on the important blanket feasibility issues, such as the MHD pressure drop, heat leakages from PbLi into the cooling helium flows, and the temperature distributions in the insulating flow insert and at the material interface. Both ITER scenarios look acceptable, i.e., all material restrictions can be easily met. In the DEMO scenario, the flow insert operates in harsh conditions causing high temperature drop in the insert and high interface temperature between the hot PbLi and the ferritic structure that may exceed the allowable material limits.
An investigation of MHD effects on a Flibe (Li
2BeF
4) simulant fluid has been conducted under the U.S.–Japan JUPITER-II collaboration program using the “FLIHY” pipe flow facility at UCLA. The ...present paper reports experimental results on turbulent pipe flow of an aqueous potassium hydroxide solution under magnetic field using particle image velocimetry (PIV) technique. The modification of turbulence was investigated by comparison of the experimental results with a direct numerical simulation (DNS) data base. The PIV measurements at Re
=
11,300 were performed with variable Hartmann numbers, and the modification of the mean flow velocity as well as turbulence reduction was observed. A flat velocity profile in the pipe center and a steep velocity gradient in the near-wall region exhibit typical characteristics of wall-bounded MHD flows. The DNS was performed approximately the same conditions and the comparison of turbulence statistics between PIV and DNS shows good agreement for up to Ha
=
10.
Silicon Carbide (SiC) has been proposed as a possible candidate material for flow channel inserts for the dual coolant blanket concept. Here, the total electrical resistance of disks of high purity ...CVD SiC were measured with liquid lead-lithium eutectic (LLE) alloy melts serving as electrodes. From this data, the relative contributions of intrinsic resistivity and surface contact resistance as a function of measurement temperature was deduced. It was shown that after a relatively short period of exposure, once wetting at the interface was achieved, that contact resistance at the SiC/LLE interface was not significant. The contact resistance during initial exposure did not behave in a repeatable consistent way and appears to be affected by small variations in sample preparation. For modeling purposes, the electrical properties of an FCI can be based on the intrinsic electrical conductivity of the material and the dimensions. However, longer term operations and effects of impurities still need to be addressed.
This paper reports on recent research into magnetohydrodynamic (MHD) phenomena applicable to fusion technology. In Europe, experiments on the relative enhancement of heat transfer in liquid metal ...(LM) flows in ducts with electrically thin or insulated walls show a factor of two increase due to strong shear flow boundary layers when compared to slug flow solutions. This increase has no associated increase in pressure drop. Stronger enhancement is possible with mechanical promoters, but pressure drop increased concomitantly. Electrical turbulence promoters have been shown in theory to aid in heat transfer as well, although preliminary experiments in Europe show no enhancement and a 20% increase in pressure drop. Experiments in Japan show that the maximum enhancement for liquid Lithium occurs for values of the interaction parameter in the
N=10–20 range. Other recent experimental efforts in Europe, Japan and Russia on natural convection in the presence of magnetic field, formation of insulator coatings and modeling of insulator imperfections are also described. In the USA, design and analysis of liquid systems utilizing all-liquid walls have lead to interest in turbulence simulations for heat transfer at free surfaces of both LMs and Flibe. Free surface flows are particularly sensitive to changes in MHD drag since no applied pressure can be used to drive the free surface flow. For this reason, Flibe is considered a prime candidate for liquid walls and is also considered in Japan as the top candidate for Large Helical Device (LHD) breeder blanket. Experimental work with Flibe simulants is currently underway in Japan, and under development in the USA. Analysis of LM flows under liquid wall conditions is being performed in the USA as well. In Russia some further experiments were made for divertor/first wall LM free surface flow, LM heat pipes and porous structures with Li evaporation.
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