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Increasing the rate of glass processing in the Hanford Tank Waste Treatment and Immobilization Plant (WTP) will allow shortening the life cycle of waste cleanup at the Hanford Site. While the WTP melters have approached the limit of increasing the rate of melting by enhancing the heat transfer rate from molten glass to the cold cap, a substantial improvement can still be achieved by accelerating the feed-to-glass conversion kinetics. This study investigates how the feed-to-glass conversion process responds to the feed makeup. By identifying the means of control of primary foam fonnation and silica grain dissolution, it provides data needed for a meaningful and economical design oflarge-scale experiments aimed at achieving faster melting.

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The combustion chamber of slagging coal gasifiers is lined with refractories to protect the steel shell of the gasifier from elevated temperatures and corrosive attack of the coal slag. Refractories composed primarily of Cr2O3 have been found most resistant to slag corrosion, but they continue to fail performance requirements. Post-mortem analysis of high-chromia refractory bricks collected from commercial gasifiers suggests that slag penetration and subsequent spalling of refractory are the cause of the short service life of gasifier refractories [1]. Laboratory tests were conducted to determine the penetration depth of three slags representative of a wide variety of coals in the United States into chromia-alumina and two high-chromia refractories. Variables tested were refractory-slag combinations and two partial pressures of O2. Slag penetration depths were measured from spliced images of each refractory. Samples heated to 1470°C for 2 hrs had maximum penetration depths ranging from 1.99±0.15 mm to at least 21.6 mm. Aurex 95P, a highchromia refractory containing 3.3% phosphorous pentoxide (P2O5), showed the least slag penetration of all refractories tested. P2O5 likely reacts with CaO and MgO in the slag, forming an immiscible Ca-Mg phosphate phase. The extraction of basic components from slag causes an increase in slag viscosity restricting the molten slag penetration into the refractory.

iii AbstractBulk vitrification (BV) is a process that heats a feed material that consists of glass-forming solids and dried low-activity waste (LAW) in a disposable refractory-lined metal box using electrical power supplied through carbon electrodes. The feed is heated to the point that the LAW decomposes and combines with the solids to generate a vitreous waste form. This study supports the BV design and operations by exploring various methods aimed at reducing the quantities of soluble Tc in the castable refractory block (CRB) portion of the refractory lining, which limits the effectiveness of the final waste form. The CRB has sufficient open porosity to allow penetration of the low viscosity molten ionic salt (MIS) that forms when the LAW waste salts melt. This penetration of MIS is the primary mechanism that allows Tc in a soluble form to migrate into the CRB.The MIS formed in significant quantities at temperatures above 300°C, remained stable until roughly 550°C where it began to thermally decompose, and was completely decomposed by 800°C. The estimated volume fraction of MIS in the feed was greater than 40%, and the CRB material contained 11 to 15% open porosity, a combination allowing a large quantity of MIS to migrate through the feed and penetrate the open porosity of the CRB. If the MIS is decomposed at temperatures below 300°C or can be contained in the feed until it fully decomposes by 800°C, MIS migration into the CRB can be avoided.Laboratory and crucible-scale experiments showed that a variety of methods can decrease MIS penetration into the CRB individually or in combination. Modification of the CRB to block MIS penetration was not deemed practical as a method to prevent the large quantities of MIS penetration seen in the full-scale (FS)-38C test but may be useful to reduce the impacts of the lower levels of MIS penetration. Modification of the BV feed materials to better contain the MIS proved to be more successful.A series of qualitative and quantitative crucible tests were developed that allowed screening of feed modifications that might be used to reduce MIS penetration. These tests showed that increasing the specific surface area of the soil (used as the primary glass-forming solid in the baseline process) by grinding stopped MIS penetration nearly entirely for feeds that contained waste simulants with lower quantities of nitrate salts. Grinding soil significantly reduced MIS penetration in feeds with higher nitrate quantities, but it was necessary to add carbohydrates (sucrose or cellulose) to destroy a portion of the nitrate at low temperatures to reach the same low levels of MIS penetration seen for the lower nitrate feeds.Developing feeds to reduce MIS penetration in FS BV applications resulted in two additional refinements. Soil-grinding to the necessary levels proved to be difficult and expensive, so the fine soil was replaced with readily available fine-grained glass-forming minerals (GFMs). Cellulose was shown to have less impact on dryer operation and was chosen as the carbohydrate ...