Self-cooled Liquid Metal Blanket Research Articles

A self-cooled liquid metal blanket for a tokamak reactor

A liquid metal-cooled inboard blanket for a tokamak reactor was designed to reduce the MHD pressure drop. No structure is directey connected to the first and second wall, so the currents induced in the first wall cooling channel return through distant sections of the blanket. The circuit resistance is very high because the current paths are long and produce a low pressure drop despite the fairly high coolant velocity. The total pressure drop through the blanket is estimated at less than 1 MPa and the heat transfer coefficient on the first wall is above 33 kW/m 2 K. The high cooling capability of the first wall is achieved without an excessive MHD pressure drop.

MHD Considerations for a Self-Cooled Liquid Lithium Blanket

The magnetohydrodynamic (MHD) effects can present a feasibility issue for a self-cooled liquid metal blanket of magnetically confined fusion reactors, especially inboard regime of a tokamak. This pressure drop can be significantly reduced by using insulated wall structure. A self-healing insulating coating has been identified, which will reduce the pressure drop by more than a factor of 10. The future research direction to further quantify the performance of this coating is also outlined.

Liquid Metal Flow Through a Right Angle Bend in a Strong Magnetic Field

AbstractIn designing a self-cooled liquid metal blanket based on the poloidaltoroidal flow concept, the magnitude of the MHD pressure drop and the character of the velocity distribution in the first wall coolant channels, that result from 3-dimensional MHD effects associated with the required right angle bends in the coolant flow, represent important design issues. To address these issues and to verify the relevant models used in the design, a joint MHD-experiment was conducted by Argonne National Laboratory (AND and Kernforschungszen-trum Karlsruhe (KfK). The test article was designed and built at ANL, and the experiments were performed at KfK’s MEKKA facility using a 3.6 Tesla superconducting solenoid magnet and a eutectic sodium potassium alloy working fluid. In the experiments, detailed voltage and pressure distributions on the duct walls and voltage distributions within the liquid metal were measured under a variety of Hartmann numbers and interaction parameters. Representative results from these mea...

Material compatibility tests with flowing Pb17Li eutectic

The material compatibility studies are related to the self-cooled liquid metal blanket concept. The studies are mainly concerned with the corrosion of the martensitic steel X18CrMoVNb 12 l (MANET) in flowing liquid Pb17Li eutectic at 500 and 550°C (773 and 823 K) in the PICOLO loop. Additional, some specimens of the austenitic steel Type 316 L(N) and of the loop material, the ferritic steel X10CrAl 7, were exposed to the eutectic alloy, the flow velocity of which was maintained at 0.3 m/s. The temperature gradient in the two tests series was 240 and 190 K, respectively. The specimens were corroded by the following liquid alloy by means of the removal of material from their surfaces. The material loss generally reaches a region of linear rates after an initial period of slower corrosion rates. It is shown that the linear rates for iron rich materials are in good agreement with rates calculated on the basis of an hydraulic model for turbulent flow conditions. The faster corrosion of the austenitic steel is due to the selective leaching of Ni and Mn out of surface layers which change their structure into the α - Fe type and get a large number of cavities. The initial period of slower corrosion seems to be related to the composition of the material. At lower Cr contents, the initial period becomes very short or disappears completely. This indicates an influence of the stability of passivation layers on the inhibition of the Pb17Li corrosion of steels.

MHD Heat Transfer in Elongated Rectangular Ducts for Liquid Metal Blankets

Laminar heat transfer in self-cooled liquid metal blankets can be enhanced by increasing the aspect ratio of the ducts. To determine the potential benefits of elongated rectangular ducts, numerical...

MHD flow in liquid-metal-cooled blankets

KfK is working on the development of a selfcooled liquid metal blanket. The basic physics of MHD-flow, its effect on heat transfer and its consequences on the design are discussed. The MHD key problems of the KfK reference concept are identified: They consist of 3-dimensional effects and channel interactions. Whereas for single channel poloidal flow a relative broad basis of data exists, the knowledge of the key problems is poore. Theoretical and experimental work has been initiated therefore to quantify them. First results on single channel flow are presented.

Numerical simulation of liquid-metal MHD flows in rectangular ducts

To design self-cooled liquid metal blankets for fusion reactors, one must know about the behaviour of MHD flows at high Hartmann numbers. In this work, finite difference codes are used to investigate the influence of Hartmann number M, interaction parameter N, wall conductance ratio c, and changing magnetic field, respectively, on the flow.As liquid-metal MHD flows are characterized by thin boundary layers, resolution of these layers is the limiting issue. Hartmann numbers up to 103 are reached in the two-dimensional case of fully developed flow, while in three-dimensional flows the limit is 102. However, the calculations reveal the main features of MHD flows at large M. They are governed by electric currents induced in the fluid. Knowing the paths of these currents makes it possible to predict the flow structure.Results are shown for two-dimensional flows in a square duct at different Hartmann numbers and wall conductivities. While the Hartmann number governs the thickness of the boundary layers, the wall conductivities are responsible for the pressure losses and the structure of the flows. The most distinct feature is the side layers where the velocities can exceed those at the centre by orders of magnitude.The three-dimensional results are also for a square duct. The main interest here is to investigate the redistribution of the fluid in a region where the magnetic field changes. Large axial currents are induced leading to the ‘M-shaped’ velocity profiles characteristic of MHD flow. So-called Flow Channel Inserts (FCI), of great interest in blanket design, are investigated. They serve to decouple the load carrying wall from the currents in the fluid. The calculations show that the FCI is indeed a suitable measure to reduce the pressure losses in the blanket.

Optimal Use of Beryllium for Fusion Reactor Blankets

The use of beryllium as a neutron multiplier for fusion reactor blankets has been analyzed. The analysis has been performed based on designs for a helium-cooled ceramic breeder and a self-cooled liquid-metal blanket, which have both been suggested for the Next European Torus reactor. It is shown that the use of beryllium in a ceramic breeder blanket is best in a “sandwich-type” arrangement, where a beryllium block is embedded between a thin ceramic layer and the thick main breeding zone, or in a homogeneous mixture of beryllium and breeding ceramics. The sandwich-type solution needs only a minimum of beryllium inventory. Monte Carlo calculations show that heterogeneity effects in such a blanket are negligible. Therefore, the “homogeneous” solution can be achieved in a more heterogeneous arrangement like slabs of beryllium with the breeding ceramics in between.The use of beryllium also provides a benefit for liquid-metal blankets, using either LiPb or lithium metal as breeding material, since neutron multiplication and the tritium breeding ratio are enhanced in such a way that it is possible to reduce the blanket thickness considerably or to replace the inboard breeding blanket by a simple neutron reflector. It turns out that in such a blanket the use of lithium metal as breeding material is superior to that of LiPb.

Turbulence and the Feasibility of Self-Cooled Liquid Metal Blankets for Fusion Reactors

Magnetohydrodynamics (MHD) considerations are of paramount importance in the design and performance of self-cooled liquid-metal (LM) blankets; the interaction between the magnetic field and the flowing LM can have a significant effect on the pressure drop, the heat transfer rate, and the corrosion rate. The purpose of the present work is to assess the implications that the recent experimental findings might have on the performance of self-cooled LM blankets. The assessment is done by considering the poloidal blanket concept, which uses a vanadium alloy for the structure. Material strength and LM compatibility considerations limit the first-wall (FW) and FW/LM interface temperature to 750/sup 0/C. When the FW is subjected to a 0.5 MW/m/sup 2/ heat flux, a temperature drop of approx. 100/sup 0/C will be established across it, restricting the FW/LM interface temperature to T/sub int/ approx. 650/sup 0/C. It is concluded that the enhanced two-dimensional turbulence might significantly increase the attractiveness of self-cooled LM blankets by enabling (a) the design of simpler and, possibly, cheaper blankets, and (b) the attainment of lower pumping power requirements and higher energy conversion efficiency.

Comparison of Three MHD Flow Control Methods for Self-Cooled Liquid Metal Blankets

The heat deposition in a blanket is concentrated near the first wall. Uniform liquid-metal velocity in a self-cooled blanket is unattractive, because it leads to low mixed-mean temperature rise through the blanket and reduced power conversion efficiency. The objective of MHD flow control is to use the electromagnetic forces to produce a non-uniform velocity distribution which gives a uniform temperature distribution over the thickness of the blanket. Three methods of MHD flow control are presented here and the MHD pressure drops corresponding to the three methods are compared. One of the methods, although successful at achieving nonuniform velocity profiles, permits a large circulation of electric current which produces a high pressure drop. The analytical results do not indicate a clear choice between the other two methods. The analytical results do point to possible difference in heat transfer performance with the two methods.

Lithium-Cooled Blankets for Advanced Tokamaks

The main objective of the Tokamak Power System Studies (TPSS) at Argonne National Lab. during fiscal year 1985 was to explore innovative design concepts that have the potential for significant enhancement of the attractiveness of a tokamak-based power plant. Activities in the area of plasma engineering resulted in a reference reactor concept, which served as a model for the impurity control and first-wall/blanket/shield studies. The liquid-metal-cooled first-wall/blanket/shield design activity was centered around the vanadium alloy structure and liquid-lithium coolant leading blanket concept as identified by the Blanket Comparison and Selection Study (BCSS). A ferritic steel structure and a LiPb breeder were considered as backup options. The magnetohydrodynamics (MHD) effects associated with self-cooled liquid-metal blanket/first-wall systems are substantially reduced by the lower magnetic fields required for higher plasmas, the lower neutron wall loading resulting from reduced power output, and the smaller reactor size of the TPSS model reactor. Therefore, improved performance characteristics of self-cooled liquid-metal blanket concepts are achievable mainly because the design constraints are more relaxed compared to the BCSS guidelines. Key aspects of the designs evaluated in the current study include the following: (1) design simplicity; (2) use of the first wall as an impurity control device; (3) modularmore » first-wall/blanket/reflector/shield construction; and (4) integrated first-wall/blanket/reflector/shield.« less

MHD Flow Control as a Design Approach for Self-Cooled Liquid-Metal Blankets of Magnetic Confinement Fusion Reactors

A self-cooled, liquid-metal blanket for a magnetic confinement fusion reactor has generally been viewed as a conventional cooling system with the additional, negative effects of the magnetohydrodynamic (MHD) interaction which must somehow be overcome. Recent studies of liquid-metal flows in strong magnetic fields have revealed the existence of characteristic surfaces in such flows. Pressure and voltage are constant to first order on these surfaces, while the surfaces are streamsurfaces for the fluid velocity. In the proposed design approach, these surfaces are used to create the flow patterns which absorb the heat where it is deposited and distribute it throughout the coolant. These MHD ''guidevanes'' can eliminate much of the complexity of previous blanket designs. Therefore, MHD effects are used as a positive design tool.

Magnetohydrodynamic Considerations for the Design of Self-Cooled Liquid-Metal Fusion Reactor Blankets

During the course of the Blanket Comparison and Selection Study, magnetohydrodynamic effects were shown to prevent not only an efficiency but also a feasibility issue for self-cooled liquid-metal blankets, especially for tokamak machines. Based on state-of-the art MHD analyses and understanding of related phenomena, designs for both mirror and tokamak machines were developed. Although details of the designs depend on specific reactor parameters, MHD related considerations were the main driver in the development of the designs. This paper presents, in a unified way, these considerations, as well as effective strategies to minimize adverse MHD effects so that they can be used as guidelines by others in future design efforts.