Behavior of Radionuclides During the Smelting of Noncombustible Solid Wastes
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BEHAVIOR OF RADIONUCLIDES DURING THE SMELTING OF NONCOMBUSTIBLE SOLID WASTES MAKOTO OSAKI AND SHINJI YOKOI Daido Steel Co., Ltd., Mutsuno, Atsuta-ku, Nagoya, Japan MINORU MIYAGAWA The Chubu Electric Power Co., Toshin-cho, Higashi-ku, Nagoya,
Japan
ABSTRACT The melting process of noncombustible solid wastes seems to be one of the most promising processes for volume reduction and immobilization. This melting process needs a 0 high temperature of around 1500 C, but the behavior of radionuclides in such a process and at such a temperature has not been fully examined. We melted small contaminated samples to examine the behavior of radionuclides. Melted products were subjected to leaching tests. Many assorted samples were melted, and we found that the vapour pressure of the radionuclide determined the distribution between melted products and dusts. The standard free energy of oxide formation and the quantity of stable nuclide of the radionuclide determined the distribution between metal and slag products. The leaching rate of melted products was sufficiently low.
INTRODUCTION With regard to the storage and disposal of noncombustible solid wastes generated by the operation of reactor, it is desirable to bring wastes to compact and stable states. Products created by the melting of wastes present the minimum volume of wastes, and provide a means for the fixation of radionuclides. So, this melting process is one of the most promising processes in treating noncombustible solid wastes. However, such a melting process requires a temperature above the melting point of steels, thermal insulators, etc. which are the greater part of the noncombustible solid wastes. The 0 processing temperature is about 1500 C. It is considerably higher than other processing temperatures, and the behavior of radionuclides in such a process and at such a temperature has not been fully examined. It is necessary to understand the behavior of radionuclides during smelting when we design, construct, run, and maintain the melting furnace, and store and dispose of the products. We have been developing a melting furnace for noncombustible solid wastes, and now we are testing a prototype melting furnace. As part of the development stage,we melted small contaminated samples with a laboratory-scale melting furnace to examine the behavior of radionuclides during smelting. These melted products were subjected to leaching tests. This paper reports the results of these " melting tests " and " leaching tests". MELTING TESTS We melted small contaminated samples in a laboratory-scale melting furnace. After cooling, we counted the activity level of metal, slag and dust to examine the behavior of radionuclides during smelting.
596 Experimental Procedure Samples. Samples were both metal and nonmetalic. Metal samples were carbon steel and SUS 304, and nonmetalic samples were silicaboard (thermal insulator), concrete and zeolite. These samples represented noncombustible solid wastes from reactors. Metal samples were sectioned from 32 mm diameter rod. Each
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