Glass waste form leaching

Of these three processes, some have received more study than others. There have been a number of determinations of leach rates (step 1) particularly from borosilicate-glass waste forms (see, for example, 1, 3), but there has been minimal effort to deter-... 

Laboratory testing at various scales, up to an engineering scale that was 1/16 the size of the planned full-scale unit, has been under way since about 2003. The objective of this testing has been to identify additives that will promote the formation of a suitable final glass waste form. It is important that the waste formed exhibit minimal leaching of radioactive components and other contaminants of concern, such as RCRA heavy metals (Buelt et al 1987 Loehr et al 1992 Thomas and Treat, 2001). 

Since the water movement will be very slow compared with the rate at which the wastes dissolve, we are concerned first and foremost with equilibrium solubility. Also, if only to relate behaviour on the geological time scale to that on the laboratory time scale, we will need to know about the mechanisms and kinetics of dissolution and leaching. The waste forms envisaged at present are glass blocks containing separated fission products and residual actinides fused into the glass and, alternatively, the uranium dioxide matrix of the used fuel containing unseparated fission products and plutonium. In the... 

Vitrification is the process of converting materials into a glass or glasslike substance. Vitrification allows for the treatment of many different kinds of waste and produces a final waste form that typically is durable and leach resistant. During the process of thermal vitrification, organic contaminants are typically destroyed, and inorganic materials are melted. 

Malow, G., Lutze, W. Ewing, R. C. 1984. Alteration effects and leach rates of basaltic glasses implications for the long-term stability of nuclear waste form borosilicate glasses. Journal of Non-Crystalline Solids, 67, 305-321. 

Altenhein, F. K., Lutze, W. Malow, G. 1981. The mechanisms for hydrothermal leaching of glass and glass-ceramic nuclear waste forms. In MOORE, J. G. (ed) Scientific Basis for Nuclear Waste Management III. Plenum Press, New York, USA, 363-370. 

Waste Form. The leach rates of radionuclides by groundwater are slow both for vitrified HLW and for SUF. A glass lifetime of at least 3000 years is expected, assuming unlimited supply of water (24). If the limited solubility of glass in groundwater is considered as well as the low water flow the lifetime would be several orders of magnitude larger. 

L. L. Hench, Leaching of Glass, Workshop on Ceramic and Glass Radioactive Waste Forms, Germantown, MD, January 1977. 

Based on dissolved ions only, the titanate waste showed an overall leach rate of x 10 5 g/cm day and a rate of 5 3 x 10 7 g/cm day for the fission waste oxides only. The results indicate that the leaching which is occurring is associated with the silicate phases in the ceramic, i.e., the Si02 formed from the silicon and the zeolite. The glass samples showed overall leach rates of 6-15 x 10 5 g/cm day and fission waste oxide leach rates of 1.8-2.7 x 10 g/cm day, where the higher rates in both cases were observed in the phosphate-containing glass. 

The leaching characteristics of the ceramic waste were compared with some vitrified waste forms under identical experimental conditions. The results are complex due to different leaching rates for various elements and the attack on the glass surface which results in the formation of a surface film which periodically sloughs off, however, some general comparison can he made. 

Leachability of a waste form is perhaps the most important criterion in considering accident situations. In the absence of salts, some of our cement products may approach the low leachability of glass. After experimenting with several methods for measuring leach rates, we selected the... 

It was estimated that the vitrification option would allow for a volume decrease of 0.75 as a conservative estimate, and that the actual volume decrease could be 0.50. Wastes would be treated in four equally sized melter systems, each of which would process about 80 tons per day. The project would be completed in about 10 years. The online operational rate is projected to be 75%, with three normally operating systems and one system down for maintenance. The produced glass does not require placement in containers, as it will pass leach test requirements in that form (D114432, Appendix A). 

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