Abstract
About 50 million gallons of high-level mixed waste is currently in storage 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 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 of in an engineered facility on the Hanford site while the IHLW product will be directed to the 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 the 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 plant availability; (4) Increasing the glass waste loading; (5) Removing sulfate from the LAW stream; (6) Operating the melter at slightly higher temperature; (7) Installing the third LAW melter into the WTP plant; and (8) Other smaller impact changes. The melter tests described in this report utilized blended feed (glass formers plus waste simulant) prepared by Optima Chemicals according to VSL specifications. Sufficient feed was prepared to produce over nineteen hundred kilograms of glass during melter tests. The nominal reductant concentration (stoichiometric ratio of 0.5 {approx} 1 mole sucrose per 16 mole NOx or 3 mole carbon per 4 mole NOx) was maintained in all the tests by the addition of sugar at VSL. The DM 10 was used to screen the optimized glass formulation with two alternative aluminum sources (kyanite and zeolite) over a wide range of target sulfur concentrations. Subsequently, based on the DM10 results, nine 12- to 34-hour DM100 tests were conducted; six with kyanite as the aluminum additive at glass sulfur concentrations ranging from 0.75 to 1.5 wt.% SO{sub 3}, and the other three with zeolite as the aluminum additive at glass sulfur concentrations ranging from 0.75 to 1.5 wt. % SO{sub 3}. The DM 100-WV melter was used in order to provide a direct comparison with the LAW tests previously conducted on the same melter. Key operating parameters such as glass temperature and production rate were held constant to investigate the sulfur incorporation into the glass and the effects of varying the aluminum additive source. The bubbling rate was adjusted to achieve a production rate of 2000 kg/m{sup 2}/day with a near-complete cold cap (90-100% of melt surface covered with feed). Quantitative measurements of glass production rates, melter operating conditions (temperatures, pressures, power, flows, etc.), and off-gas characteristics (NOx, SO{sub 2}, CO, particulate load and composition, and acid gases) were made for each test. Glass samples taken from the glass pool and the discharge chamber were inspected throughout testing to determine the limit of salt-free operation in the melter.
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