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Published: 2010

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About 50 million gallons of high-level mixed waste is currently stored in underground tanks at The United States Department of Energy's (DOE's) Hanford site in the State of Washington. The Hanford Tank Waste Treatment and Immobilization Plant (WTP) will provide DOE's Office of River Protection (ORP) with a means of treating this waste by vitrification for subsequent disposal. The tank waste will be separated into low- and high-activity waste fractions, which will then be vitrified respectively into Immobilized Low Activity Waste (ILAW) and Immobilized High Level Waste (IHLW) products. The ILAW product will be disposed in an engineered facility on the Hanford site while the IHLW product will likely be directed to a national deep geological disposal facility for high-level nuclear waste. The ILAW and IHLW products must meet a variety of requirements with respect to protection of the environment before they can be accepted for disposal. The Office of River Protection is currently examining options to optimize the Low Activity Waste (LAW) Facility and LAW glass waste form. One option under evaluation is to enhance the waste processing rate of the vitrification plant currently under construction. It is likely that the capacity of the LAW vitrification plant can be increased incrementally by implementation of a variety of low-risk, high-probability changes, either separately or in combination. These changes include: (1) Operating at the higher processing rates demonstrated at the LAW pilot melter; (2) Increasing the glass pool surface area within the existing external melter envelope; (3) Increasing the glass waste loading; and (4) Operating the melter at a slightly higher temperature. The Vitreous State Laboratory (VSL) of The Catholic University of America (CUA) and Energy Solutions, Inc. have evaluated several of these potential incremental improvements for ORP in support of its evaluation of WTP LAW facility optimization. Some of these incremental improvements have been tested at VSL including increasing the waste loading, increasing the processing temperature, and increasing the fraction of the sulfur in the feed that is partitioned to the off-gas (in the event that a decision is made to break the present WTP recycle loop). These approaches successfully demonstrated increases in glass production rates and significant increases in sulfate incorporation at the nominal melter operating temperature of 1150 C and at slightly higher than nominal glass processing temperatures. Subsequent tests demonstrated further enhancement of glass formulations for all of the LAW waste envelopes, thereby reducing the amount of glass to be produced by the WTP for the same amount of waste processed. The next phase of testing determined the applicability of these improvements over the expected range of sodium and sulfur concentrations for Hanford LAW. This approach was subsequently applied to an even wider range of LAW wastes types, including those with high potassium concentration. The feasibility of formulating higher waste loading glasses using SnO2 and V2O5 in place of Fe2O3 and TiO2 as glass former additives was also evaluated. The present report provides data from investigation of the effects of magnesium content (up to (almost equal to)10 wt%) on LAW glass properties and from work to identify improved high waste loading glass formulations that meets all processing and product quality requirements for two waste compositions. The scope of testing is detailed in the Test Plan for this work. A glass composition previously developed and tested at VSL for LAW from tank AN-105 (LAWA187) was varied by substituting Mg for other glass former additives such as Ca, B and Si in an attempt to formulate a glass with improved properties, such as higher waste loading and greater sulfur tolerance. The results were used to reformulate another glass (ORPLG9) developed for LAW from tank AP-101 that contains high concentrations of alkalis (Na and K). Glass formulation goals for this waste were to increase the sulfur tolerance of the glass as well as to decrease refractory corrosion. Each of the two final glass compositions was evaluated to determine the maximum amount of sulfur that can be incorporated into the glass through melter testing. The results from these tests together with earlier work for ORP were evaluated to develop recommendations for the work scope necessary to modify and update the WTP LAW glass formulation correlation algorithm.