Development of a Ceramic Waste Form for High-Level Waste Disposal
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Water
Zeolite A
Zeo lite Dry e r &Dre Heated Mixer
Dried Zeolite A
r V-Mixer
Salt (LiC1-KC1, etc.) from fuel treatment
Salt-Loaded Zeolite (remains in V-mixer) Glass Frit
Vibratory Compactor
Salt-Loaded Zeolite & Glass Frit in an open HIP Can Figure 1
Salt Loaded Zeolite & Glass Frit in Loading Container
-•i[
Crimper/ Vacuum Furnace/ Welder
V-Mixer
Hot Isostatic Press (HIP)
Flowsheet of the Ceramic Waste Form Production Process
ceramic waste form are relatively simple ( see Figure 1). The first piece of equipment in the flowsheet is the zeolite dryer. Zeolite A naturally occludes more than 20 wt.% water. The water is removed before the zeolite is contacted with the salt in an attempt to facilitate the occlusion of salt into zeolite. Different systems have been utilized to dry zeolite A, with batch sizes ranging from 5 to 34 kg. In all drying systems the zeolite was heated to 550'C at 20 C/min under a vacuum. The minimum drying cycle time has been determined to be 12 hours. Powdered zeolite with an average particle size of less than 10 ýtm was used in initial development work. However, due to perceived handling difficulties and to achieve better packing in the HIP can before processing, a standard particle size distribution having a mean in the range of 75 to 170 ýtm was defined. To increase the efficiency of mixing, the salt from the electrorefiner is milled to a similar mean particle size using a mill/classifier from Prater Industries, Inc. (Cicero, IL). A cyclone separator is used to collect the salt after milling. Experimentation has determined that the mill and classifier should be set at speeds of 1500 and 500 rpm, respectively, to deliver an acceptable mean particle size. The salt from the milling and the dried zeolite are combined in a heated V-mixer. Salt is occluded into the zeolite by heating to more than 500'C while mixing at 15 rpm. The capacity of the V-mixer is more than 50 kg of powder, but it is typically operated with 4.1 kg of salt and 31 kg of dried zeolite. The materials are rotated in the V-mixer and then heat is applied to increase
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the temperature to 500'C. This state is maintained for up to 15 hours in order to occlude the molten salt into the zeolite structure. After cooling, typically 25 wt.% glass frit is added to the salt-loaded zeolite and the materials are cold-mixed. The blended materials are loaded into cans that are eventually processed in a hot isostatic press (HIP). A vibratory compactor is utilized to increase the packing density of the mixture in the HIP can to approximately 50 percent of theoretical. Next the can is heated to 500'C and evacuated for up to 6.0 hours. The tube used to fill the can is crimped and welded, providing a sealed, evacuated can for processing in the HIP. The HIP used for the demonstration project was manufactured by ABB Autoclave Systems, Inc. (Columbus, OH). The operating gas is argon, and the HIP chamber is 15.2 cm in diameter and 30.5 cm in height. The HIP is capable of reaching a maximum temperature of 1450'C and a maximum pressu
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