The State of Development of Waste Forms for Mixed Wastes U.S. Department of Energy's Office of Environmental Management (1999) / Chapter Skim
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4. Waste Treatment and Stabilization
4. Waste Treatment and Stabilization
Pages 41-69
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From page 41... ...
The MWFA methodology to identify and provide mixed waste treatment technologies in support of EM's cleanup goals were presented in two documents, both entitled "Mixed Waste Focus Area Technical Baseline Report" (DOE, 1996a and DOE, 1997a)
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From page 42... ...
The MWFA has categorized the current inventory of EM's mixed waste into five groups, based on waste characteristics that require similar handling, treatment, and associated activities. This allows the assignment of generalized treatment technologies (for example, waste water treatments)
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From page 43... ...
The Advanced Mixed Waste Treatment Project being constructed at the Idaho National Engineering and Environmental Laboratory (INEEL) by the private contractor British Nuclear Fuels, Ltd., exemplifies a major privatization initiative, as described in Box 3.
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From page 44... ...
44 The State of Development of Waste Forms .
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From page 45... ...
45 ~ -o =.O o ~ [L au i~ au .
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From page 46... ...
.3 A large number of treatment processes and a considerable number of possible waste forms resulting from these processes are applicable to mixed wastes. Table 5 summarizes the treatment and waste form options that MWFA has identified for its five mixed waste groups.
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From page 47... ...
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From page 48... ...
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From page 49... ...
wastes. In MWFA planning, these processes are presented as available baseline technologies that may be applied to mixed waste (DOE, ~ 997b)
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From page 50... ...
In this process, organic compounds are destroyed, leaving an ash residue containing Inorganic salts, metals, and radionuclides. Secondary wastes from this process include filtered solids, volatilized Articulates and mercury, activated carbon, and ion exchange resins.
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From page 51... ...
Debris can include manufactured objects, plant or animal matter, or natural geologic material. The debris treatment group represents about 46% of EM's mixed waste.
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From page 52... ...
The extremely broad physical, chemical, and radiological properties of EM's mixed waste may preclude the use of generically designed treatment processes. Waste forms that result from use of these technologies are described, along with other available waste forms, in the next section.
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From page 53... ...
Metals such as iron, copper, and nickel have been used as metallic baths and commercial scale mixed waste processing has been demonstrated. The high temperature of the process requires close attention to the off-gas streams, depending on the composition of the feed to the process.
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From page 54... ...
The second method, stabilization of elemental mercury with sulfur polymer cement, was being demonstrated at Brookhaven National Laboratory. The development of direct stabilization technologies to provide waste forms for disposing of elemental mercury recovered from mixed wastes is a priority item in the MWFA technology development needs list described later in this chapter and reproduced in Appendix C
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From page 55... ...
The basic classes of waste forms include: Grout Glass Polymers Crystalline ceramics Vitreous ceramics Compacted wastes For most treated mixed wastes in the EM inventory, one or more of the above waste forms can meet the requirements of chemical durability, for example, leach resistance and long-term stability, physical strength and fracture resistance, and resistance to radiation damages (Mayberry and Huebner, 1993; Ewing, et al., 19951. Compatibility with the waste stream is a primary consideration in selecting among the available waste forms.
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From page 56... ...
In the following parts of this section, each waste form will be described, along with its advantages, disadvantages, and state of development. Cement-Based Grout Grout stabilization is now the process of choice for most of the routine mixed waste stabilization operations at DOE sites.
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From page 57... ...
For grout waste forms, the increase in waste volume caused by the cement itself and any required additives may be a factor in their selection. The cost penalty for disposing of a greater volume of waste forms that contain Tow waste loading can be evaluated against the cost of additional treatment to remove troublesome constituents or selecting a different matrix that is more compatible with the waste stream.
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From page 58... ...
Glass forms are desirable because they offer Tow release rates and mechanical and thermal stability in the near-surface disposal environment. Because most waste constituents dissolve in the molten glass at typical processing temperatures ranging from 1100 °C to 1500 °C, high waste loading is possible, and the waste is retained in the resulting matrix, even if the waste form is disturbed or mechanically damaged.
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From page 59... ...
Key parameters such as waste loading, viscosity, melt temperature, and durability are interrelated. Higher temperature increases the solubility of practically all waste constituents in the molten glass and, within limits, increases the achievable waste loading and homogeneity of the resulting waste form, but higher temperature also increases corrosion of the processing equipment.
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From page 60... ...
Sulfur cement is a recently developed polymer consisting of 95% sulfur and organic monomer that may be especially useful for mercury. Microencapsulated wastes are less likely to retain their dimensional stability than grout waste forms, and they generally require secondary containers to provide physical strength.
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From page 61... ...
, however, there has been little deployment of this technology for waste management at DOE sites. Phosphate-bonded ceramics that can be made at room temperature and show promise for immobilizing mixed wastes have recently been developed with financial support of the MWFA (Wagh, et al., 1997; Singh, et al., ~ 9981.
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From page 62... ...
The need for waste characterization could not be avoided to the extent hoped, and therefore the process showed no overall advantage compared to the more established technologies for making grout or glass waste forms (John Kolts, personal communication to NRC staff, October 19981. Although plasma-heated systems may have applications at some DOE sites, their widespread deployment for mixed waste treatment is no longer being pursued by the MWFA.
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From page 63... ...
It was pointed out in Chapter 2 that the committee considers quantitative knowledge of the EM mixed waste inventory to be deficient, and that definition of detailed flowsheets for waste treatment and stabilization is not possible without this Information. If waste to be treated is not well defined, only the most robust processes, such as vitrification or formation of vitreous ceramics, can be selected with confidence, and the process must be designed for conservative (possibly low and less efficient)
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From page 64... ...
Based on MWFA's presentations to the committee (Appendix By, information in the section on Available Waste Forms, and the judgments of its members, the committee foment that available classes of treatment methods and waste forms are sufficiently developed to accommodate DOE's current and expected mixed waste inventory. There is, however, a continuing need for improved engineer~ng adaptation of these technologies to the actual mixed waste streams they are intended to treat.
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From page 65... ...
MWFA has recognized the need for better characterization of EM's mixed waste inventory, but it has not explicitly addressed the trade-off between detailed characterization and robust treatment processes that could accept more heterogeneous waste streams. MWFA has not given sufficient attention to the engineering work necessary to adapt existing or new technologies to operation with radioactive materials and to demonstrate these technologies on a production scale.
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From page 66... ...
Better characterization of EM's mixed wastes can reduce uncertainties in the composition of the waste streams to be treated. This in turn should allow design of simpler treatment processes that accept a more narrow range of waste compositions.
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From page 67... ...
. Although assessing privatization was not within the committee's task, plans for the Advanced Mixed Waste Treatment project were presented to the committee and the committee learned that EM expects a large fraction of the mixed waste inventory to be treated by private contractors.
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From page 68... ...
Clearly no single form is appropriate for all wastes, but, collectively, the variety of available waste forms and well-established waste form production technologies make it unlikely that any totally new class of waste forms will be necessary to complete EM's planned cleanup program. Grout waste forms, for example, can accommodate essentially all mixed wastes in the inventory, although pre-treatment is required for some wastes (e.g., organics)
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From page 69... ...
. The committee recommends the following: · MWFA should integrate individual treatment technologies being developed for its five treatment groups into an overall mixed waste management system.
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