First Results of In-Can Microwave Processing Experiments for Radioactive Liquid Wastes at the Oak Ridge National Laborat
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FIRST RESULTS OF IN-CAN MICROWAVE PROCESSING EXPERIMENTS FOR RADIOACTIVE LIQUID WASTES AT THE OAK RIDGE NATIONAL LABORATORY*
T. L. WHITE, E. L. YOUNGBLOOD, J. B. BERRY, AND A. J. MATFUS Oak Ridge National Laboratory, P. 0. Box 2009, Oak Ridge, TN 37831-8071
ABSTRACT The Oak Ridge National Laboratory (ORNL) Waste Handling and Packaging Plant is developing a microwave process to reduce and solidify remote-handled transuranic (RH-TRU) liquids and sludges presently stored in large tanks at ORNL. Testing has recently begun on an in-drum microwave process using nonradioactive RH-TRU surrogates. The microwave process development effort has focused on an in-drum process to dry the RH-TRU liquids and sludges in the final storage container and then melt the salt residues to form a solid monolith. A 1/3-scale proprietary microwave applicator was designed, fabricated, and tested to demonstrate the essential features of the microwave design and to provide input into the design of the fullscale applicator. Conductivity cell measurements suggest that the microwave energy heats near the surface of the surrogate over a wide range of temperatures. The final wasteform meets the waste acceptance criteria for the Waste Isolation Pilot Plant, a federal repository for defense transuranic wastes near Carlsbad, New Mexico.
INTRODUCTION The ORNL Waste Handling and Packaging Plant (WHPP) [1] at Oak Ridge National Laboratory (ORNL) is a facility that will process and repackage remote-handled transuranic (RH-TRU) liquid and solid wastes from ORNL and solids from other sites for shipment to the Waste Isolation Pilot Plant (WIPP) [2]. The liquid RH-TRU wastes, stored in stainless steel tanks, consist of a watery supernatant/sludge mixture containing mostly NaNO3 with the remaining compounds consisting of a complicated soup of chemicals that contain the RH-TRU wastes. The WHPP liquids processing flow sheet calls for evaporation of the free water in the wastes followed by melting of the salt residues. The cooled melt will form a solid monolith because of the binding action of the NaNO3 on the remaining solids. The final waste volume will be much less than the original waste volume because of water removal and consolidation/melting of the salt residues. The wasteform satisfies the WIPP waste acceptance criteria (WAC) [3] which state that no free particulates or liquids should be present in the final wasteform (currently the WIPP WAC allow soluble salts containing TRU waste to be stored). The temperature of the melt must be limited to prevent the destruction of the nitrates into NOx gases which would necessitate extensive offgas scrubbing systems for the WHPP. In the conceptual design stage, the WHPP process required RH-TRU liquid evaporation and melting to be performed by conventional wiped-film evaporators or extruders. More detailed descriptions of the development of the conventional WHPP processes are reported elsewhere [4]. In this concept, microwaves would be used only to maintain the temperature in a drum during filling operations. Last ye
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