Glass as a Waste Form and Vitrification Technology Summary of an International Workshop (1996) / Chapter Skim
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2 Three Futures for Glass
2 Three Futures for Glass
Pages 8-18
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From page 8... ...
Discussion of glass in these three containment roles makes what has been accomplished in previous decades more readily apparent. It also allows more explicit definition of what remains to be accomplished in developing the appropriate scientific basis for understanding glass behavior and technology needs for the full-scale Incorporation of nuclear waste into glass.
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From page 9... ...
The reaction of glass with water involves a number of different processes, including exchange of alkali metal ions in the glass with hydronium ions from water, matrix dissolution of the glass, formation of altered surface layers on the glass (including adsorption, structural changes, and mineral precipitation onto the surface) , and changes in solution composition.
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From page 10... ...
The layer may become a chemical sink for released radionuclides due to the precipitation of phases, or it may be a physical barrier to diffusive Toss of radionuclides. During Stage III, formation of surface hydration layers, adsorption of chemical species, and surface precipitation of crystalline phases (Figure 3)
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From page 11... ...
aggregates along void and cavity linings, and B-domains consist of needle-like crystallites (also smectite) in an amorphous matrix.
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From page 12... ...
, not containing radionuclides, subjected to vapor phase alteration for nearly 1,000 days (from workshop poster by Gong et al., abstract included in Appendix E)
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From page 13... ...
Although refinements in the models may be forthcoming, major changes in the understanding of glass corrosion are not expected. · The glass alteration models used in perfommance assessments must be generally applicable to a wide range of glass compositions under a variety of laboratory conditions, as well as diverse natural geochemical environments.
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From page 14... ...
In particular, the French computer model "LIXIVER" shows that, in silica-saturated solutions or for low silicon diffusion in gel layers, nuclear waste glasses may be orders of magnitude more durable than was previously expected. If the conclusions of such models can be confirmed by further research (e.g., long-term experiments on waste glasses or studies of natural glasses)
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From page 15... ...
The issue of radiation effects on nuclear waste glasses was the subject of a workshop sponsored by the Council on Materials Science under the auspices of the U.S. Department of Energy in February 1996.
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From page 16... ...
Because the glass logs may be in interim storage for a number of years before a repository is selected, built, and ready to accept the waste canisters, it is prudent to archive samples that can be used to study phenomena related to the aging of the glass. FUTURE 2: AN EFFECTIVE, BUT NOT NECESSARILY THE PRIMARY BARRIER TO LONG-TERM RELEASE This ''filture'' for glass as a waste form represents the role presently played by glass in most nuclear waste disposal strategies.
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From page 17... ...
Essential differences include: · The chemical durability requirements involved in this scenario are for shorter periods of time. This means, for example, that differences in extrapolated or interpolated results between different models of glass corrosion would be of less or even minor importance.
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From page 18... ...
Waste glass formulations may be chosen to simplify plant operation, reduce capital costs of construction and operation, and ensure ease and cost effectiveness for the dismantling and disposal of the vitrification plant. However, research may have important impacts on the technology, such as in the development of longer-lived melters and improved operating conditions.
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