Initial Demonstration of the Vitrification of High-Level Nuclear Waste Sludge Containing an Organic Cs-loaded Ion-Exchan
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INITIAL DEMONSTRATION OF THE VITRIFICATION OF HIGH-LEVEL NUCLEAR WASTE SLUDGE CONTAINING AN ORGANIC Cs-LOADED ION-EXCHANGE RESIN N. E. BIBLER, J. P. BIBLER, M. K. ANDREWS, and C. M. JANTZEN Westinghouse Savannah River Co., Aiken, SC, 29802 ABSTRACT When immobilizing into borosilicate glass the radionuclides in the caustic high-level radioactive wastes stored in the USA, the soluble fission product Cs-137 has to be removed from supernates of the wastes. In the current processes zeolites or an organic precipitant will be used to remove the Cs. These are then treated further and mixed with the radioactive sludges and vitrified into a borosilicate glass. This paper describes the vitrification of a mixture resulting from using a new process to remove Cs from the caustic supernate. A resorcinol based organic ion exchange resin is used. This resin was then mixed with sludge and frit and vitrified. Using an organic ion exchange resin rather than zeolite or the organic precipitant has certain advantages. For example, use of the zeolite increases the amount of glass to be made and use of the organic precipitant produces benzene as a secondary waste stream. Results in the paper indicate that a mixture of the resin, sludge and frit can be successfully vitrified in a joule-heated, slurry fed melter. However, when resin is present in the feed, the glass becomes less durable due to the increased amount of Fe(II) caused by reduction of Fe(III) in the melt. Based on the durabilities of other waste glasses, this glass is still suitable as a canistered wasteform. INTRODUCTION At the Hanford, West Valley, and the Savannah River Site (SRS), high-level radioactive nuclear wastes will be immobilized into borosilicate glass for permanent disposal in a geologic repository. At all three sites, the wastes are stored as caustic slurries in million gallon underground tanks. Since the slurries are caustic, most of the fission products and the transuranic waste radionuclides are precipitated in a sludge as hydrous oxides; however, since Cs is soluble in caustic slurries, most of the radioactive Cs- 137 is in the supernate along with high concentrations of Na+ ions (-4M) added as NaOH. Consequently, Cs-137 has to be removed from the supernate and consolidated with the sludge in order to immobilize all the radioactivity into the glass. At Hanford and West Valley, an inorganic zeolite mineral is used in the reference process to remove Cs. This zeolite will be mixed with sludge and an appropriate frit and then fed into a melter at 1150'C. The supernates at Savannah River Site (SRS) are too caustic to allow the use of zeolite. Cesium will be precipitated as cesium tetraphenylborate (CsTPB). Potassium is also precipitated from the supernate as KTPB. The tetraphenylborate precipitates will then be decomposed by hydrolysis. This produces benzene which is removed in order to reduce the amount of carbon going into the melter. The product of this hydrolysis will be mixed with the sludge and frit and then fed to a melter. Recently, an organic ion exchange r
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