Vitrification of High-Level Radioactive Waste in a Small-Scale Joule-Heated Ceramic Melter
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VITRIFICATION OF HIGH-LEVEL RADIOACTIVE WASTE IN A SMALL-SCALE JOULE-HEATED CERAMIC MELTER* GERALD B. WOOLSEY AND M. JOHN PLODINEC E. I. du Pont de Nemours & Co., Savannah River Laboratory, Aiken, South Carolina, USA
ABSTRACT Vitrification is the reference process for the immobilization of radioactive waste from the production of defense materials at the Savannah River Plant (SRP). Since 1979, a small vitrification facility (1 lb/hr) has been operated at the Savannah River Laboratory using actual SRP waste. In previous studies. dried waste was fed to this smaller melter. This report discusses direct feeding of actual liquid-waste slurries to the small melter. These liquidfeeding tests demonstrated that addition of premelted glass frit to the waste slurry reduces the amount of material volatilized. Results of these tests are in accord with results of large-scale tests with actual waste.
INTRODUCTION Radioactive waste produced from reprocessing nuclear fuel for defense programs at the Savannah River Plant (SRP) is stored in large underground tanks on the plant site. This alkaline waste is made up of three components. The bulk of the waste actinides and fission products is contained in an insoluble sludge of hydroxides and hydrous oxides of iron, aluminum, and manganese [1-3]. The rest of the waste is either in the form of a crystalline salt cake or a nearlysaturated supernatant salt solution. This supernatant solution contains 95% of the radiocesium and traces of other radionuclides [4]. Methods to immobilize SRP waste for long-term storage are presently being developed at the Savannah River Laboratory (SRL). It is currently envisioned that the waste will be immobilized in two stages. This will reduce the initial capital investment and allow the most efficient use of limited resources. Since -95% of the radionuclides are contained in the insoluble sludge, the first stage will be designed to immobilize the sludge. A second stage for processing highlevel waste salt would be built a few years later. According to the current reference process, sludge (washed free of soluble salts) will be mixed with glass-forming chemicals (in the form of premelted borosilicate glass frit). This slurry will be heated to drive off excess water, then fed to a Joule-heated ceramic melter. Here the slurry will be dried and dissolved in the molten frit. The glass formed will be continuously poured out of the melter into stainless steel canisters. -These canisters will be welded closed and then stored onsite on an interim basis. Eventually they would be shipped to a Federal repository for permanent storage. Since 1977, SRL has been performing continuous melting tests with simulated waste using both large-scale and small-scale equipment. In early 1979, SRL began processing actual waste in a small-scale glass plant in hot cells
The information contained in this article was developed during the course of work under Contract No. DE-AC09-76SR00001 with the U.S. Department of Energy.
604 (capacity -1 lb/hour). In earlier work [5], a
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