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    공학 >정밀ㆍ에너지 >원자력공학
  • 강의학기
    2013년 1학기
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    2,726
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This graduate course teaches students the key aspects of the vitrification of radioactive wastes.
Waste glass requirements
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  • 이전차시
  • 다음차시

차시별 강의

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1. 비디오 Waste glass requirements The purpose of nuclear waste vitrification is explained. The need to immobilize the hazardous and radioactive materials is stressed. The three major issues are identified: 1) glass formulation for easy processability and high product quality, 2) rapid glass making in an electrical melter, 3) understand the long-term release of radionuclides from the waste glass. URL
비디오 Vitrification technology overview The history of legacy waste from Pu production is reviewed and historical development of waste vitrification in key countries is outlined. Basic methods of vitrification are elucidated, including the Korean induction heated hot crucible melter. URL
2. 비디오 Glass properties overview The requirements imposed on waste glass are stated in terms of melt and glass property constraints. The individual properties are reviewed and characterized. URL
비디오 Waste glass formulation Selection of glass-forming and modifying additives to make processable and acceptable glass is explained and mathematically formulated. Waste loading maximization is related to waste cleanup lifecycle and repository cost. URL
3. 비디오 Viscosity and electrical conductivity The key processing properties, viscosity and electrical conductivity, are characterized as functions of temperature and composition. Various ways of these functional representations are described. URL
비디오 Glass transition temperature Glass transition is explained and the glass transition temperature (Tg) is defined. The relevance of Tg for waste glasses with respect to radiolytic heating and glass crystallization is clarified. URL
4. 비디오 Glass crystallization Basic concepts of nucleation and growth of crystals are introduced and the most frequently encountered crystals are reviewed. Nucleation rate, growth rate, and dissolution rate are defined and both graphically and mathematically represented. URL
비디오 Liquidus temperature While phase equilibria must not be neglected, melter processing occurs out of equilibrium, and thus kinetics is of the primary importance. Therefore, kinetic equations and TTT diagrams are shown. Liquid-liquid immiscibility is also mentioned. URL
5. 비디오 Glass corrosion The complexity of glass corrosion requires deep knowledge of diffusion, interfacial heterogeneous reaction, and hydrothermal precipitation of minerals in highly multicomponent media. Basic concepts and relations are introduced. URL
비디오 Chemical durability Only short-term resistance of glass against corrosion (durability) can be measured in the laboratory using a series of standardized tests. Long-term (over 105 to 106 years) durability can only be assessed. URL
6. 비디오 crystallization and chemical durability Waste glass crystallization must not degrade glass durability. Therefore, canister-centerline cooled glasses are tested pro durability. Out of many crystalline forms, nepheline appears the most insidious. URL
비디오 Waste glass processing Waste glass technology differs from commercial glass technology in many aspects: the waste is given, only additive raw materials can be selected; feed may be charged in the form of slurry; fining is not essential; etc. URL
7. 비디오 Melter feed makeup Mineral form of additives and particle size influence cold cap stability and the rate of melting. Drainage of fluxes can destabilize the cold cap, leading to cold cap freezing. Evolved gases produce foam and cavities under the cold cap. URL
비디오 Melting reactions Melting reactions release copious gasses and produce intermediate crystalline forms. Eutectic melts of molten salts attack refractory particles. Glass-forming melt tends to trap gases, creating foam. Melter feed reacts while moving down across the cold cap as the heat is conducted upward. URL
8. 비디오 Batch calculation Glass component can be present in more than one batch material. Matrix calculus is used for designing complex batches. Back calculation is essential. Feed simulants must be carefully designed. URL
비디오 Thermal analysis Thermogravimetric analysis (TGA) and differential scanning calorimetry (DCS) measure the kinetics of batch reaction. Batch reactions are multiple and overlapping. Evolved glass analysis (EGA) allows gas-evolving reactions to be identified. URL
9. 비디오 X-ray diffraction and microscopy Optical and electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray diffraction (XRD) are used for the identification of crystalline phases in glasses and in glass batches (melter feeds) during their conversion to molten glass. URL
비디오 Segregation of molten salts As nitrates and carbonates decompose, areas occupied by molten salts shrink leaving behind sulfates, chromates, pertechnetates, chlorides). These sparsely-soluble components accumulate in droplets and are transported to the melt surface. URL
10. 비디오 Silica (quartz) dissolution Quartz, the major feed component, initially reacts with molten salts and then dissolves in melt via diffusion. Diffusion is affected by the formation, growth and motion of gas bubbles. Large grains tend to cluster. URL
비디오 Volatilization Volatile species evaporate from the cold cap and escape from the melt to bubbles and the atmosphere. Their Henry’s coefficients are large. The rate of volatilization is controlled by diffusion both in gas and melt. Buoyancy-driven and surface-tension-gradient-driven convection in melt enhance volatilization. URL
11. 비디오 Redox equilibria Multivalent species are common in waste glasses. Redox reactions generate oxygen bubbles and metal droplets. Redox ratio increases as temperature increases and optical basicity decreases. URL
비디오 Foaming Batch gases generate primary foam, redox reaction lead to secondary foam. Foam accumulated under the cold cap slows the melting process by reducing heat transfer. Foam collapses through met drainage and breaking the liquid films separating foam cells. URL
12. 비디오 Settling of solids Solids of crystalline phases (spinel) can settle on the melter bottom and can block the melt discharge. Crystals settle while growing and dissolving in the melt and form a dense sludge that can be electrically conductive. URL
비디오 Glass melters Joule-heated melters use resistance heating via inconel electrodes. Induction-heated melters generate heat electromagnetically either in the crucible wall or within the melt. URL
13. 비디오 Modeling The basic balance laws with constitutive relations form a system of coupled field equations to be solved for problems defined by the boundary conditions. Mathematical models of melters display the electric, temperature, and velocity fields in molten glass and furnace atmosphere. Models can also include redox equilibria, bubble behavior, and solid particle growth, dissolution, and settling. URL
Refractory end electrode corrosion Molten glass and salts corrode refractory walls of melters by dissolving refractory materials via diffusion under free or forced convection. Intergranular diffusion is also common. Surface tension gradients drive melt-line corrosion and bubble/droplet drilling.
14. Revision Topics selected by students are further elucidated.

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