Determination of the Structure of Vitrified Hydroceramic/CBC Waste Form Glasses Manufactured from DOE Reprocessing Waste
The selection of a glass-making option for the solidification of nuclear waste has dominated DOE waste form programs since the early 1980's. Both West Valley and Savannah River are routinely manufacturing glass logs from the high level waste inventory in tank sludges. However, for some wastes, direct conversion to glass is clearly not the optimum strategy for immobilization. INEEL, for example, has approximately 4400 m{sup 3} of calcined high level waste with an activity that produces approximately 45 watts/m{sup 3}, a rather low concentration of radioactive constituents. For these wastes, there is value in seeking alternatives to glass. An alternative approach has been developed and the efficacy of the process demonstrated that offers a significant savings in both human health and safety exposures and also a lower cost relative to the vitrification option. The alternative approach utilizes the intrinsic chemical reactivity of the highly alkaline waste with the addition of aluminosilicate admixtures in the appropriate proportions to form zeolites. The process is one in which a chemically bonded ceramic is produced. The driving force for reaction is derived from the chemical system itself at very modest temperatures and yet forms predominantly crystalline phases. Because the chemically bonded ceramic requires an aqueous medium to serve as a vehicle for the chemical reaction, the proposed zeolite-containing waste form can more adequately be described as a hydroceramic. The hydrated crystalline materials are then subject to hot isostatic pressing (HIP) which partially melts the material to form a glass ceramic. The scientific advantages of the hydroceramic/CBC approach are: (1) Low temperature processing; (2) High waste loading and thus only modest volumetric bulking from the addition of admixtures; (3) Ability to immobilize sodium; (4) Ability to handle low levels of nitrate (2-3% NO{sub 3}{sup -}); (5) The flexibility of a vitrifiable waste; and (6) A process that is based on an industry with decades of practical experience. The research undertaken in the present investigation builds on a previous study under the NEER program. The earlier studies identified an optimal formulation for the immobilization of the calcine that is both compositionally adequate to retain radionuclides as well as hazardous constituents and which has a reaction rate that will allow the technical employment of the process. The study established in a general way the glass-forming region in the system M{sub 2}O-MO-Al{sub 2}O{sub 3}-SiO{sub 2} (M{sub 2}0 = alkali metal oxides; MO = alkaline earth metal oxide) which provides the base for these hydroceramic/CBC materials (Fig. 1). The objectives of the present program are to track the structural changes that take place during formulation, chemical reaction, and HIPing. Compositions must be varied through the glass-forming region, structures of the crystals and glass matrix of the glass-ceramic determined, and the structural characteristics in turn related to stability and leachability of the final products.
- Research Organization:
- Pennsylvania State Univ., University Park, PA (United States)
- Sponsoring Organization:
- USDOE - Office of Nuclear Energy, Science and Technology (NE)
- DOE Contract Number:
- FG07-01ID14105
- OSTI ID:
- 859219
- Report Number(s):
- DOE-00001; TRN: US0702233
- Country of Publication:
- United States
- Language:
- English
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