Waste Forms Technology and Performance Final Report (2011) / Chapter Skim
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4 Waste Processing and Waste Form Production
4 Waste Processing and Waste Form Production
Pages 87-118
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From page 87... ...
Instead, this chapter presents some key unit operations/technologies that have been or could potentially be used to produce nuclear waste forms. The following waste processing technologies are described in this chapter, and their key attributes are summarized in Table 4.1: • Joule-heated melters • Cold crucible induction melters • In-container vitrification • Self-sustaining vitrification • Cold pressing and sintering • Hot uniaxial pressing • Hot isostatic pressing 1 A given waste processing technology is "more efficient" compared to a baseline technology when, for example, it enables higher material throughputs or higher waste loadings; accommodates higher levels of feed stream variability or liquid feed streams; accommodates higher levels of incompatible elements; results in reduced secondary wastes; is more operationally robust; or is less expensive.
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Cold Crucible C Large Borosilicate glass, glassInduction Melter ceramic materials, other (CCIM) glass types (LaBs, FeP, AIP, chalcognide, and others)
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are present; may require secondary wastes; mature industrial precalcining or pretreating waste to an oxide process form (shrinkage handled by bellows like canisters) continued
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• Fluidized bed steam reforming • Other thermal technologies • Mix and set technologies Cold crucible induction melters, hot isostatic pressing, and fluidized bed steam reforming technologies were discussed in the committee's interim report (NRC, 2010)
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The Defense Waste Processing Facility (DWPF) at the Savannah River Site is the largest production JHM ever built.
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Melt rates can also be increased by increasing melt temperatures. JHMs can be operated at ~1,200°C before different materials of construction are required.
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Partial dry feeding will also be used to improve melt rate. The primary advantages of JHMs for waste immobilization are their high production rates and ability to produce waste form material of consistent quality.
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They can be fitted with stirrers to facilitate melt pool convection and homogenization so that crystals do not accumulate in one location in the melt pool. CCIMs can also be used in conjunction with other technologies.
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CCIM is an emerging technology for the vitrification of fission product solutions and decontamination waste streams. It also has potential applications for processing metallic waste streams (Vernaz, 2009)
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. ICV requires soil- or glass-formers to establish the melt and create a stable, vitrified waste form.
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For example, water removal is required to avoid excess gas generation and ensure the uniformity of the resulting waste form. Because it does not require expensive equipment, SSV can be particularly useful for immobilizing small-volume waste streams or wastes that are difficult to immobilize by other methods.
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The use of organic binders and lubricants with the powder will also minimize density gradients but requires processing of the waste stream to introduce these materials and thermal treatment of the pressed products to remove the organic components. For the development of waste forms, the CP&S offers several advantages: it uses inexpensive equipment, is easily adaptable to small batches of waste, and is particularly well suited to laboratory studies of potential phases for waste forms such as glass ceramic material (Juoi et al., 2008; Staples et al., 2007)
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Notably, it produces monolithic waste forms with substantially reduced volumes compared to untreated waste streams. Because the waste is processed in a sealed can, there are no volatile emissions.
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However, additional studies are needed to demonstrate the safety and compatibility of this technology with specific waste streams and also to address its scalability to high-volume waste streams. 4.8 FLUIDIZED BED STEAM REFORMING A bed of granular material can be made to exhibit fluid-like properties by passing a liquid or gas through it.
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Its applications include several unit operations such as drying, heating/cooling, particle coating, and chemical reactions. Applications of fluidized bed technology in nuclear fuel production, recovery, and waste processing date back to the late 1950s and early 1960s.
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If kaolinite is added to an alkali-rich waste (e.g., neutralized HLW) during processing,9 a crystalline ceramic waste form is produced that is composed of sodium-aluminum-silicon feldspathoid mineral analogues (e.g., sodalite)
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, which could produce waste forms with good radionuclide retention properties and increased waste loadings relative to borosilicate glass (Jantzen, 2006)
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. 4.9.2 Electric Arc Furnaces Electric Arc Furnaces are primarily used in metallurgy and can also produce vitrified waste forms (O'Connor and Turner, 1999)
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4.10 MIX AND SET TECHNOLOGIES Waste forms can be generated by mixing wastes with materials that cure and solidify, encapsulating the waste and also binding some waste constituents in hydration product phases. Several binding materials can serve as waste forms.
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For in-line mixing, the cement and liquid waste are mixed and then pumped into containers as thick slurries. Cementitious waste forms are being used for the immobilization of radioactive waste in the DOE-EM cleanup program; two noteworthy examples are the Saltstone process at Savannah River Site, where waste salt solutions are mixed with fly ash, slag, and Portland cements and pumped into cement vaults for disposal.
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A hydroceramic waste form (Bao et al., 2005) is formulated in the same fashion as zeolites (i.e., from metakaolinite and sodium hydroxide)
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: fluidized bed steam reforming, cold crucible induction melting, and hot isostatic pressing. These waste form production technologies are being used commercially in both nuclear and/or nonnuclear applications, as described elsewhere in this chapter, and appear to be applicable for processing and immobilizing a range of DOE-EM waste
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The committee concurs with DOE-EM about the applicability of these technologies in the cleanup program. Even though these are mature technologies and have applications in different industries, some development work will be needed to use them in processing nuclear waste as described in the interim report (NRC, 2010)
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Fluidized Bed Steam N N Y Y Reforming (FBSR) Calcining N N N Y Hydrothermal N N Y Y Processing Mix and Set N N N N NONTHERMAL
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111 WASTE PROCESSING AND WASTE FORM PRODUCTION Cements Zeolites (OPC, Metal Hydro- Ceramicrete, and Matrix ceramic Others) Bitumen Geopolymers N N N N N N N N N N Y N N N N Y Y N N N Y Y N N N N Y N N N N N N N N N Y Y N Y N N Y [to include Y (heating Y [to include use of as waste necessary to use of as waste forms and as melt bitumen)
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The first one operates in a reducing environment, and its function is to evaporate the liquid nuclear waste stream; destroy organics; reduce nitrates, nitrites, and nitric acid to nitrogen gas; and form a stable solid waste product. The first-stage fluidized bed of the FBSR process is referred to as the Denitration and Mineralization Reformer, or DMR.
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. Because the Cl, SO4, and/or S2 are chemically bonded and physically restricted inside the sodalite cage structure, these species do not readily leach out of the respective FBSR waste form mineral phases.
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Indeed, waste stabilization at Idaho National Laboratory currently uses a glass-bonded sodalite ceramic waste form (CWF) for disposal of electrorefiner wastes for sodium-bonded metallic spent nuclear fuel from the EBR II fast breeder reactor.
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2008. "Feasibility Evalu ation and Retrofit Plan for Cold Crucible Induction Melter Deployment in the Defense Waste Processing Facility at Savannah River Site–8118," WM2008 Conference, Phoenix, Ariz.
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2003. Disposition of Tank 48H Organics by Fluidized Bed Steam Reforming (FBSR)
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1994. Comparison of Ceramic Waste Forms Produced by Hot Uniaxial Pressing and by Cold Pressing and Sintering, UCRL-JC-117039, CONF -941075-8, Lawrence Livermore National Laboratories, Livermore, Calif.
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2009. "Ceramic and Phosphate Glass Waste Forms and Cold Crucible Melting Technology," presented at the Committee on Waste Forms Technology and Performance, Meeting #3, November 4, 2009, Washington, D.C.
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