NUCLEAR WASTE VITRIFICATION EFFICIENCY COLD CAP REACTIONS
The cost and schedule of nuclear waste treatment and immobilization are greatly affected by the rate of glass production. Various factors influence the performance of a waste-glass melter. One of the most significant, and also one of the least understood, is the process of batch melting. Studies are being conducted to gain fundamental understanding of the batch reactions, particularly those that influence the rate of melting, and models are being developed to link batch makeup and melter operation to the melting rate. Batch melting takes place within the cold cap, i.e., a batch layer floating on the surface of molten glass. The conversion of batch to glass consists of various chemical reactions, phase transitions, and diffusion-controlled processes. These include water evaporation (slurry feed contains as high as 60% water), gas evolution, the melting of salts, the formation of borate melt, reactions of borate melt with molten salts and with amorphous oxides (Fe{sub 2}O{sub 3} and Al{sub 2}O{sub 3}), the formation of intermediate crystalline phases, the formation of a continuous glass-forming melt, the growth and collapse of primary foam, and the dissolution of residual solids. To this list we also need to add the formation of secondary foam that originates from molten glass but accumulates on the bottom of the cold cap. This study presents relevant data obtained for a high-level-waste melter feed and introduces a one-dimensional (1D) mathematical model of the cold cap as a step toward an advanced three-dimensional (3D) version for a complete model of the waste glass melter. The 1D model describes the batch-to-glass conversion within the cold cap as it progresses in a vertical direction. With constitutive equations and key parameters based on measured data, and simplified boundary conditions on the cold-cap interfaces with the glass melt and the plenum space of the melter, the model provides sensitivity analysis of the response of the cold cap to the batch makeup and melter conditions. The model demonstrates that batch foaming has a decisive influence on the rate of melting. Understanding the dynamics of the foam layer at the bottom of the cold cap and the heat transfer through it appears crucial for a reliable prediction of the rate of melting as a function of the melter-feed makeup and melter operation parameters. Although the study is focused on a batch for waste vitrification, the authors expect that the outcome will also be relevant for commercial glass melting.
- Research Organization:
- Hanford Site (HNF), Richland, WA (United States)
- Sponsoring Organization:
- USDOE Office of Environmental Management (EM)
- DOE Contract Number:
- DE-AC27-08RV14800
- OSTI ID:
- 1025335
- Report Number(s):
- ORP-49512-FP Rev 0; TRN: US1104834
- Journal Information:
- JOURNAL OF NON-CRYSTALLINE SOLIDS, Conference: THE 19 UNIVERSITY CONFERENCE ON GLASS SCIENCE -- GLASSES FOR ENERGY RENSSELAER POLYTECHNIC INSTITUTE & THE AMERICAN CERAMIC SOCIETY 08/02/2011 THRU 08/05/2011 TROY NY
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BORATES
BOUNDARY CONDITIONS
CERAMIC MELTERS
CERAMICS
CHEMICAL REACTIONS
DISSOLUTION
EFFICIENCY
EVAPORATION
GLASS
HEAT TRANSFER
MATHEMATICAL MODELS
MELTING
MOLTEN SALTS
OXIDES
RADIOACTIVE WASTES
SENSITIVITY ANALYSIS
VITRIFICATION
WASTES