Cement waste forms

Rubin, J. B. Carey, J. W. Taylor, C. M. V. Enhancement of Cemented Waste Forms by Supercritical C02 Carbonation of Standard Portland Cements. Proceedings of the American Nuclear Society 1st Topical Meeting on Decommissioning, Decontamination, Reutilization of Commercial Government Facilities, Knoxville, TN, Sept. 7-12, 1997. 

Disposal facilities for nonhazardous waste (e.g., municipal/indus-trial landfills) normally are constructed without substantial engineered barriers, such as a rock cover or cement waste forms, that would deter inadvertent intrusion into waste, and the waste itself often is in a readily accessible physical form. Therefore, in determining exempt waste, scenarios for inadvertent intrusion involving permanent occupancy of disposal sites and normal human activities that could access waste would be appropriate. Examples include excavation in the construction of homes and permanent residence on... 

As may be seen from Table 17.8, Cs was added either as CsNOs or CsCl in the first three waste streams, whereas the form of Cs was not known in the last case, but certainly it was soluble because it was detected in wastewater. The TCLP results indicate that Cs, although added as nitrate or some other soluble form, is well immobilized. The LI is not as high as 18 that was reported by Bamba et al. [27] for a glass waste form, but it is certainly higher than the minimum of 6 expected from cement waste forms [28]. 

Promising forms will be heated for several months at the normal storage temperature and at 100°G to determine possible ill effects. The maximum specific power of cement waste forms would be / 0.4 W/1. with normal storage temperatures around 60°C. 

Allen PG, Siemering GS, Shuh DK, Bucher JJ, Edelstein NM, Langton CA, Clark SB, Reich T, Denecke MA (1997c) Technetium speciation in cement waste forms determined by X-ray absorption fine structure spectroscopy. Radiochim Acta 76 77-86... 

Dissolution/precipitation Leaching experiments EQ3/6 Rel.7.2a package Leaching from cemented waste forms [5]... 

Sulfur polymer cement shows promise as an encapsulation and stabilization agent for use with low level radioactive and mixed wastes. Use of SPC allows accommodation of larger percentages of waste than PCC. As of this writing (1997), SPC-treated waste forms have met requirements of both the Nuclear Regulatory Commission (NRC) and the Environmental Protection Agency (EPA). 

Ceramicrete cures to create final waste forms that are analogs of naturally occurring phosphate minerals. These minerals have been shown to be relatively insoluble over geologic time scales. The final waste form is stronger than typical room temperature, hydraulic cements and performs in the manner of high-temperature fused ceramics. The technology has been evaluated in bench-and operational-scale tests on contaminated wastewater, sedimenL ash, and mixed wastes. 

Disposal costs at various radioactive waste management facilities in the United States range from 20/ft to 1500/ft. ANL used an average disposal cost of 60/ft of treated waste form to estimate the total disposal costs for the hypothetical Ceramicrete prodnct. The estimated cost was 2836/m of waste. According to the ANL, this fignre is lower than the disposal costs for cement, which were estimated at 3700/m (D20934H, p. 15). 

BNL claims that polyethylene encapsulation allows for greater waste loading and has a better waste form performance than conventional cement solidification, allowing for 70% fewer drums to be processed and shipped for disposal of some government waste streams. The technology is commercially available. 

For the cement stabilization option, a facility would be constmcted to dewater and treat the wastes. There would be a 7- to 21-day staging period of wastes for quality assurance operations. An online rate of 250 days a year was assumed. It is estimated that cement stabilization would result in a volume factor increase roughly 3.75 times the total volume of waste treated. This increase in volume is necessary to immobilize technetium present in the wastes and to achieve a final waste form that could withstand pressures of 500 pounds per square inch (psi). The cement would be placed in 4-ft by 4-ft by 8-ft steel containers that would serve as a mold and to facilitate the handling of the finished blocks (D114432, Appendix A). 

The successful production of a nonleachable glass waste form from mixed low-level waste allows land disposal of the waste at a lower cost than the baseline technology (cementation) if it were used to stabilize the waste. This savings is primarily due to the large waste volume reductions realized during vitrification. In addition, glass final waste forms have been shown to have decreased teachability and increased structural stability as compared to the baseline waste form. 

Low- and intermediate-level waste is currently converted to cement and bitumen waste forms, but the existing trend is toward an increase in the radiation safety levels and reliability of immobilization. From this point of view, LILW should also be incorporated in vitreous and crystalline matrices. Current Russian and US experience on vitrification of such waste demonstrates the potential of the melting/vitriflcation process. Major advantages of vitrification over bituminization and cementation are a greater waste volume reduction, higher productivity, and higher durability of the final product. 

Jiang, W Wu, X. Roy, D. M. 1993. Alkali activated fly ash - slag cement based nuclear waste forms. Materials Research Society Symposium Proceedings, 294, 255-260. 

Glasser, F. P. 1993. Chemistry of cement-solidified waste forms. In Spence, R. D. (ed) Chemistry and Microstructure of Solidified Waste Forms. Lewis, Boca Raton, 1 -39. 

Many cements used today are composites of Portland cement and industrial waste materials that can enter into the hydration reactions and contribute to the strength of the hardened product. These substances include pulverized fuel ash (PFA) from burning of pulverized coal in thermal power stations, crushed blast-furnace slag (Section 17.7), and natural or artificial pozzolanas—that is, volcanic ash and similar finely particulate siliceous or aluminosilicate materials that can react with the Ca(OH)2 in Portland cement to form hydrated calcium silicates and aluminates. As noted earlier, the solubility of Ca(OH)2 is such that the pH of pore water in Portland cements will be about 12.7, at which the Si-O-Si or Si-O-Al links in the solid pozzolanas will be attacked slowly by OH- to form discrete silicate and aluminate ions and thence hydrated calcium silicate or aluminate gels. 

Hartmann, T. Paviet-Hartmann, P. Rubin, J. B. Fitzsimmons, M. R. Sickafus, K. E. The Effect of Supercritical Carbon Dioxide Treatment on the Leachability and Structure of Cemented Radioactive Waste-Forms. Waste Manage. 1999, 19, 355-361. 

Solidification with cement generally is accomplished with a Portland cement and other additives. The quantity of cement can be varied according to the amount of moisture in the waste. Heavy metal cations in the waste form insoluble carbonates and hydroxides at the high pH of the mixture. The surface of the hardened mass can be coated with asphalt or other material to reduce leaching of hazardous components. If the waste is mixed with anhydrous cement and water there is the possibility of ions incorporation in the cement structure during the hydrolysis process. Heavy metal ions could bind with the cement by the process of chemisorption, precipitation, surface adsorption,... 

Poon CS, Lio KW (1997) The limitation of the toxicity characteristic leaching procedure for evaluating, cement-based stabilized/solidified waste forms. Waste Manage 17 ... 

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