Curium / Actinides / Carbonate complexation / Fluorescence spectroscopy
SummaryThe carbonate complexation of Cm(III) is investigated by means of time resolved laser fluorescence spectroscopy (TRLFS) at 25°C in 1 m NaCl as a function of the carbonate concentration. In the first set of experiments, the carbonate concentration is controlled by the C0 2 equilibrium partial pressure, (pC0 2 = 10-1000 mbar) and pH whereas the second set of batch experiments is performed at higher carbonate concentrations ([CO §~] > 10 4 molal). Both data sets overlap in the intermediate range and fit well together. The carbonate complexes CmCOJ, Cm(C0 3 ) 2 and Cm(C0 3 ) 3~ are quantified spectroscopically in the trace concentration range by peak deconvolution of fluorescence emission spectra. At pC0 2 = 500 or 1000 mbar and pH < 6.5, there is evidence for the formation of a Cm(III) bicarbonate complex to a small extent. Up to pH 9.5 there is no indication for the formation of mixed hydroxo carbonate complexes. At high carbonate concentrations (> 0.1 molal), the formation of an additional complex, Cm(C0 3 )4~, is indicated. The stability constants determined in 1 molal NaCl solution are found to be: logy?(CmHCO! + ) = 1.9; logy?(CmC0 3 + ) = 5.90; log0(Cm(CO 3 ) 2 ) = 10.27; log^(Cm(C0 3 )D = 13.18; log/? (Cm(C0 3 )D = 14.18.
The disposal of low-level radioactive waste (LLRW) entails financial and safety risks not common to most market commodities. This manifests debilitating uncertainty regarding future waste volume and disposal technology performance in the market for waste disposal services. Dealing with the publicly perceived risks of LLRW disposal increases the total cost of the technology by an order of magnitude, relative to traditional shallow land burial. Therefore, this analysis first examines five proposed disposal facility designs and quantifies the costs associated with these two important sources of uncertainty. Based upon this analysis, a marketable disposal permit mechanism is proposed and analyzed for the purpose of reducing market uncertainty and thereby facilitating a market solution to the waste disposal problem. In addition to quantifying the costs, the results illustrate the ways in which the design of a technology is influenced by its institutional environment, and vice versa.
The solubility and speciation of Pu(VI) with phosphate is being investigated to determine the ability of phosphate to act as an actinide getter. In the initial studies performed, solubility was approached from oversaturation at an initial pH = 4, 10 and 13.4. Absorption spectra were recorded, the solution filtered, and the filtrate analyzed for Pu content. Absorption spectra were obtained at varying phosphate concentrations, and at pH of 2.7 to 11.9. The effect of complexation on the 833 nm Pu(VI) band was characterized. Evidence for three phosphate complexes was obtained for pH < 10, which have absorption bands at 842, 846 and 849 nm. Evidence for colloid formation was observed, but is not conclusive. The possible presence of colloids prevented an accurate determination of true solubility. A concentration of 10−5 to 10−6M Pu(VI) was measured in solutions at pH ≤ 10 that was filtered with a 50 nm filter. Pu(VI)-phosphate complexes predominated at pH ≤ 11.6. At higher pH, however, only hydrolyzed Pu(VI) was detected. At pH = 12, the concentration of Pu(VI) was as high as 10−4M.
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