Corrosion Resistance of Refractories in Melts of Glasses Used to Immobilize Radioactive Wastes

Abstract

Results are presented from tests of the corrosion resistance of fused-cast zircon-bearing and high-chromium refractories in melts of borosilicate and phosphate glasses used to immobilize radioactive waste products (RWP). It is shown that high-chromium refractories Kh-99 and KhPL-85 can be recommended for use in lining the most important sections of the melters employed in RWP vitrification.The increasing worldwide demand for energy in the Twenty-First Century can be partially met by making greater use of nuclear power, which would inevitably also increase the amount of radioactive wastes that is formed. Immobilizing radioactive waste products (RWP) is a serious concern in all countries with a nuclear power industry [1]. It is common practice throughout the world for highly active RWP to be immobilized by vitrification. The technology was first used on an industrial scale in the USSR in 1987 at the "Mayak" Chemical Combine [2]. The vitrification technology has been used to immobilize high-activity wastes for almost 30 years and makes it possible to significantly reduce the total volume of the wastes while converting them to a form that is resistant to environmental effects and is suitable for long-term storage and final burial. The technology is based on the electrical formation of glass from solutions of the wastes and fluxes in a direct-heating glassmaking furnace (ceramic melter) at 1150°C and transfer of the glassy product to thick-walled steel containers for cooling, long-term storage, and subsequent burial. The glass matrix has a large capacity for immobilizing different radionuclides (fission products) and is stable over a long period of time.The glasses used to immobilize RWP should have a relatively low boiling point, include the maximum possible amount of RWP while remaining resistant to the effects of chemicals, heat, and radiation, and possess adequate mechanical strength. These requirements are met by two types of inorganic glasses: boron-silicate glasses and phosphate glasses. Boron-silicate glasses have been most widely used to immobilize wastes that exhibit high or moderate levels of radioactivity. These glasses are based on a three-dimensional silica-oxygen framework. Boron acts as a modifier that lowers the boiling point and increases the strength of the glass. The boiling point of boron-silicate glasses is (1100 ± 100)°C and the boiling point of phosphate glasses is (1000 ± 100)°C. Phosphate melts are regarded as being more corrosive to ceramic refractories.Factories that vitrify RWP are in operation in Russia, the U. S., Great Britain, and Japan. Most of the attention in these facilities' operation is paid to improving the designs of the melters, and the most important feature of the melters is the use of corrosion-resistant materials. Data on the operation of the "Pamela" facility in Belgium [3], the WVDP demonstration project near West Valley, New York (in the U. S.), the VEK plant in Germany [5], the TVF unit in Japan [6], and the DWPF facility near the Savannah River in the U. S. [7] shows ...