"A Study on Instability Phenomena in Liquid Metal Natural Convection under a Magnetic Field."

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A use of liquid metals as the blanket material in a magnetic confined fusion nuclear reactor has many advantages on the high heat transfer characteristics and the tritium breeding in the blanket designs. However, the MHD pressure drop in the blanket is high due to the high electrical conductivity of the liquid metals and extremely high pump power is required when the blanket is cooled by a sigle phase liquid metal flow. To avoid the high pump power, many conceptual designs on the blanket have been proposed. There are many problems which have not been solved on thermal hydraulcs of liquid metals under magnetic fields, especially flow characteristics have not been clarified since liquid metals are opaque to optical rays. It has been generally reported that the heat transfer is suppressed by the applied magnetic fields as the flow is suppressed by Lorents force. While, a few papers reported that large temperature fluctuation was occured and the heat transfer was augmentated in natural and … More forced convections by the applied magnetic field. These phenomena have not been clarified yet since the flow visualization is difficult.This study was started to clarify the heat transfer augmentation mechanism, which has not been well understood generally, by visualizing the flow using neutron radiography. Neutron radiography is suitable to visualize the liquid metal flows by a tracer and a dye-injection method.In this report, the liquid metal flow visualizations in natural convection and under a magnetic field were carried out and following results were obtained.1) It was shown that the flow of lead-bismuth eutectics was visualized by a tracer and a dye-injection method.2) Lead-bismuth-gas two-phase flow in a container under a horizontal magnetic field was visualized and the void fraction and the flow field measurements were carried out. The applied magnetic field up to 2500 gauss affected the void fraction distribution a little but suppressed the flow. It was shown that flow phenomena in a liquid metal in the presence of a magnetic field was visualized bu nentron radiography.3) Flow vector fields in lead-bismuth in a container could be obtained by a tracer method using a correlation method when the tracer sizes was closed to the image element size in the image processing. Less