Iron-Enriched Basalt for Containment of Nuclear Wastes
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BASIS
FOR
NUCLEAR WASTE
MANAGEMENT
tephen V. Topp, editor
IRON-ENRICHED BASALT FOR CONTAINMENT OF NUCLEAR WASTES J. M. WELCH, R. P. SCHUMAN, C. W. SILL, P. V. KELSEY, JR., S. P. HENSLEE, R. L. TALLMAN, R. M. HORTON, D. E. OWEN, AND J. E. FLINN, EG&G Idaho, Inc., P.O. Box 1625, Idaho Falls, ID 83415 ABSTRACT Iron-enriched basalt (IEB) has been investigated as a containment medium for defense transuranic (TRU) and defense high-level wastes (HLW). IEB samples have been fabricated incorporating simulated and actual defense TRU wastes generated at the Rocky Flats Plant (RFP), and simulated defense high-level wastes. These samples were tested for leaching resistance and fracture toughness. Cesium and strontium volatility from an IEB melt was also assessed, using radioactively spiked samples. INTRODUCTION Scientists at EG&G Idaho, Inc., prime contractor at the Idaho National Engineering Laboratory (INEL), are developing iron-enriched basalt (IEB), a man-made rock (referred to as iron-enriched because of an iron content higher than that of natural basalt), as a medium for the containment of a variety of nuclear wastes [1,2]. Several years of laboratory- and pilot-plant-scale tests have shown that IEB can be readily prepared by melting 0a variety of noncombustible wastes, with selected oxide additions, at 1500 C [3]. Holding the melt at this temperature results in thorough homogenization of the melt constituents. The melt can then be cast into monoliths and subjected to a controlled cooling cycle to produce a largely devitrified, stable, and durable waste form similar in appearance and composition to natural basalt. This paper reviews the results of recent work on the immobilization of two distinct types of nuclear wastes in IEB: defense transuranic waste and defense high-level waste. Defense transuranic (TRU) wastes are highly heterogeneous actinide-contaminated wastes generated at the Department of Energy's (DOE) Rocky Flats Plant (RFP). One of the principal wastes is a sludge produced by precipitation from the plant's liquid waste streams. Defense highlevel wastes (HLW), generated from the reprocessing of defense reactor fuels, are produced at a number of facilities, including DOE's Idaho Chemical Processing Plant (ICPP), which produces a dry, calcined product, and the Savannah River Plant (SRP), which yields a wet sludge. Since preparation of IEB requires relatively high temperatures (14001500'C), the potential for cesium and strontium loss from high-level waste was investigated by spiking an IEB melt with 137 Cs and 8 5 Sr, and determining the rate at which cesium and strontium volatilize as a function of temperature. EXPERIMENTAL METHODS
The IEB waste form specimens were prepared by blending actual or simulated waste (dried at 200%C if necessary) with dry metal oxide additives to approach the nominal IEB composition while maintaining the waste as a major component. Samples weighing 50 to 200 g were melted in air in resistance-
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heated furnaces. The melts were subjected to a variety of heating, cooling,
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