Radioactive waste distribution ratio

Extraction of neptunium, plutonium, and americium from simulated radioactive liquid waste was carried out in particular with tert-butyl and dealkylated tetramers, hexamers, and octamers of calixarene [ethoxy(diphenylphosphine oxide)]. Among these six calixarenes, the highest distribution ratios were obtained with the dealkylated calix[8]arene. Using a different sample of the dealkylated hexamer, the Strasbourg group concluded that this compound is the most efficient. This discrepancy can be explained by the presence of impurities, detected by NMR, which were probably responsible for the poor performances of the dealkylated hexamer tested at Cadarache. 

They reported the distribution ratios (Dm) of lanthanide and actinide ions and compared the Dm values with that of Am " in the extraction system of 1 M HNO3 and 0.1 M TODGA/ M-dodecane as shown in Table 18.11. The order of extractability of actinide ions from 1 M HNO3 is An, An > An02 > An02. The TODGA has an ability of co-extraction of trivalent actinide ions and lanthanide ions from high-level liquid radioactive waste. 

Removal of cesium from medium-level radioactive wastes involves extraction of cesium from aqueous solutions which are 1 M in HNO3 and 4 M in NaNOa (8). In a preliminary study, extraction experiments with ligands 1-7 were performed by mixing equal volumes (5 to 7 mL) of aqueous and organic solutions (calixarene 10 M in 2-nitrophenyl hexyl ether or 2-NPHE) in sealed polypropylene tubes for one hour at room temperal re (25 1 C). The aqueous solutions contained either NaNO or CSNO3 (5.0x10 M) in HNO3 (1 M) to assess the selectivity toward cesium in the hypothetical presence of sodium. A measure for the selectivity was assumed to be the ratio of the distribution coefBcients obtained separately for both cations ... 

Optical microscope observations have shown that zircons often exhibit extremely complex microstructures (on the scale of 1-100 /tm), in which changes of birefringence correlate with the distribution of U and Th (Chakoumakos et al. 1987). However, no attempts appear to have been made to relate these microstructures to other impurities (such as water-related species) and crystal defects, both of which may significantly influence the processes of metamictization and recrystallization. Such a study involving TEM might also provide important information about the diffusion and leaching of radioactive impurities (and the products of their decay), processes that have important implications for ceramic nuclear-waste disposal and for techniques of age determination based on measurements of Pb/U isotopic ratios. 

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