THE COLD CRUCIBLE MELTER: HIGH-PERFORMANCE WASTE VITRIFICATION

摘要

The idea of heating glass directly by Joule effect arose in response to one of the major concerns of the nuclear power industry, which is to limit the temperature of the containment materials in order to maximize their service life and minimize the production of secondary waste. Glass is generally heated by Joule effect using electrodes in the furnace chamber or immersed directly in the melt. Although this classic design has been adopted in many countries to vitrify nuclear waste, its major disadvantage when the glass is melted inside a refractory vessel is the deterioration and ultimate disposal of the melter, which constitutes a cumbersome wasteform. Joule heating can also be implemented through direct induction in the glass by means of a suitable electromagnetic field. In this case, the glass may also be contained in a cooled structure that is transparent to the field: this is the operating principle of the Cold Crucible Melter (CCM), -which allows direct Joule heating of the glass within a solidified glass shell formed on contact with the cooled melter wall. The CEA and COGEMA have developed melters of this type to fabricate glasses and glass-ceramics, initially for the vitrification .of high-level fission product solutions. This technique has progressively been applied to reactor waste, including solid and liquid materials, both organic and inorganic. It is capable of melting, refining and pouring glasses of all types at unlimited temperatures with virtually no melter corrosion. The devices now in operation can reach glass fabrication rates of several hundred kilograms per hour, and there are no obvious technical obstacles to the design of units capable of melting one metric ton or more per hour. Several test facilities are now available today at Marcoule, in France, to vitrify organic or inorganic solid and liquid waste. COGEMA is considering the use of this type of melter in one of its vitrification units at La Hague, and other industrial applications are planned in Europe and Asia. Cold crucible melters could unquestionably be used very competitively to vitrify the thousands of cubic meters of solutions and tons of fission product calcines now stored in the United States.