Sergey Smolentsev

On the exploration of innovative concepts for fusion chamber technology

Abstract This study, called APEX, is exploring novel concepts for fusion chamber technology that can substantially improve the attractiveness of fusion energy systems. The emphasis of the study is on fundamental understanding and advancing the underlying engineering sciences, integration of the physics and engineering requirements, and enhancing innovation for the chamber technology components surrounding the plasma. The chamber technology goals in APEX include: (1) high power density capability with neutron wall load >10 MW/m 2 and surface heat flux >2 MW/m 2 , (2) high power conversion efficiency (>40%), (3) high availability, and (4) simple technological and material constraints. Two classes of innovative concepts have emerged that offer great promise and deserve further research and development. The first class seeks to eliminate the solid “bare” first wall by flowing liquids facing the plasma. This liquid wall idea evolved during the APEX study into a number of concepts based on: (a) using liquid metals (Li or Sn–Li) or a molten salt (Flibe) as the working liquid, (b) utilizing electromagnetic, inertial and/or other types of forces to restrain the liquid against a backing wall and control the hydrodynamic flow configurations, and (c) employing a thin (∼2 cm) or thick (∼40 cm) liquid layer to remove the surface heat flux and attenuate the neutrons. These liquid wall concepts have some common features but also have widely different issues and merits. Some of the attractive features of liquid walls include the potential for: (1) high power density capability; (2) higher plasma β and stable physics regimes if liquid metals are used; (3) increased disruption survivability; (4) reduced volume of radioactive waste; (5) reduced radiation damage in structural materials; and (6) higher availability. Analyses show that not all of these potential advantages may be realized simultaneously in a single concept. However, the realization of only a subset of these advantages will result in remarkable progress toward attractive fusion energy systems. Of the many scientific and engineering issues for liquid walls, the most important are: (1) plasma–liquid interactions including both plasma–liquid surface and liquid wall–bulk plasma interactions; (2) hydrodynamic flow configuration control in complex geometries including penetrations; and (3) heat transfer at free surface and temperature control. The second class of concepts focuses on ideas for extending the capabilities, particularly the power density and operating temperature limits, of solid first walls. The most promising idea, called EVOLVE, is based on the use of a high-temperature refractory alloy (e.g. W–5% Re) with an innovative cooling scheme based on the use of the heat of vaporization of lithium. Calculations show that an evaporative system with Li at ∼1 200°C can remove the goal heat loads and result in a high power conversion efficiency. The vapor operating pressure is low, resulting in a very low operating stress in the structure. In addition, the lithium flow rate is about a factor of ten lower than that required for traditional self-cooled first wall/blanket concepts. Therefore, insulator coatings are not required. Key issues for EVOLVE include: (1) two-phase heat transfer and transport including MHD effects; (2) feasibility of fabricating entire blanket segments of W alloys; and (3) the effect of neutron irradiation on W.

Application of the “K–ε” model to open channel flows in a magnetic field

Abstract In magnetohydrodynamic (MHD) flows turbulence reduction occurs due to the Joule dissipation. It results in heat transfer degradation. In open channel flows, heat transfer degradation is also caused by the turbulence redistribution near the free surface. Both effects can be significant in fusion applications with low-conductivity fluids such as molten salts. In the present study, the “K–e” model equations for turbulent flows and the free surface boundary condition are adjusted with taking into account MHD effects. Different orientations of the magnetic field, perpendicular and parallel to the main flow, have been considered. The model coefficients have been tuned by a computer optimization using available experimental data for the friction factor. The effect of free surface heat transfer degradation due to the turbulence redistribution has been implemented through the variation of the turbulent Prandtl number. As an example, the model is used for the analysis of a turbulent MHD flow down an inclined chute with the heat flux applied to the free surface.

Liquid magnetohydrodynamics — recent progress and future directions for fusion

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.

Magnetohydrodynamic and Thermal Issues of the SiCf/SiC Flow Channel Insert

Abstract In the dual-coolant lead lithium (DCLL) blanket, the key element is the flow channel insert (FCI) made of a silicon carbide composite (SiCf/SiC), which serves as electric and thermal insulator. The most important magnetohydrodynamic (MHD) and thermal issues of the FCI, associated with MHD flows and heat transfer in the poloidal channel of the blanket, were studied with numerical simulations using the U.S. DEMO DCLL design as a prototype. The mathematical model includes the two-dimensional momentum and induction equations for a fully developed flow and the three-dimensional (3-D) energy equation. Two FCI modifications, one with no pressure equalization openings and one with a pressure equalization slot, have been considered. The computations were performed in a parametric form, using the electric and thermal conductivity of the SiCf/SiC as parameters. Under the DEMO reactor conditions, parameters of the FCI have been identified that result in low MHD pressure drop and low heat leakage from the breeder into the helium flows. This paper also discusses the role of the pressure equalization openings, 3-D flow effects, and the effect of SiCf/SiC anisotropy.

On the flow past a magnetic obstacle

This paper analyses numerically the quasi-two-dimensional flow of an incompressible electrically conducting viscous fluid past a localized zone of applied magnetic field, denominated a magnetic obstacle . The applied field is produced by the superposition of two parallel magnetized square surfaces, uniformly polarized in the normal direction, embedded in the insulating walls that contain the flow. The area of these surfaces is only a small fraction of the total flow domain. By considering inertial effects in the analysis under the low magnetic Reynolds number approximation, it is shown that the flow past a magnetic obstacle may develop vortical structures and eventually instabilities similar to those observed in flows interacting with bluff bodies. In the small zone where the oncoming uniform flow encounters the non-negligible magnetic field, the induced electric currents interact with the field, producing a non-uniform Lorentz force that brakes the fluid and creates vorticity. The effect of boundary layers is introduced through a friction term. Due to the localization of the applied magnetic field, this term models either the Hartmann braking within the zone of high magnetic field strength or a Rayleigh friction in zones where the magnetic field is negligible. Finite difference numerical computations have been conducted for Reynolds numbers

DEVELOPMENT OF THE LEAD LITHIUM (DCLL) BLANKET CONCEPT

\hbox{\it Re}\,{=}\,100

The Fusion Nuclear Science Facility, the Critical Step in the Pathway to Fusion Energy

and 200, and Hartmann numbers in the range

Development Status of a SiC-Foam Based Flow Channel Insert for a U.S.-ITER DCLL TBM

1 \le \hbox{\it Ha} \le 100

Characterization of the effect of Froude number on surface waves and heat transfer in inclined turbulent open channel water flows

(

Study of instabilities and quasi-two-dimensional turbulence in volumetrically heated magnetohydrodynamic flows in a vertical rectangular duct

\hbox{\it Re}