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The study of uranium oxides at different conditions is of paramount importance in the nuclear field, especially regarding characterization of the spent nuclear fuel behavior in dry storage scenarios. This paper reports results of XRD and Raman analysis on four powdered samples prepared in order to cover a specific stoichiometry range in UO2+x, i.e. x = 0.24, 0.26, 0.28 and 0.30. XRD results reveal a clear increase of the average tetragonal distortion with the increase in oxidation degree, with the main phase detected for all the samples being a weakly tetragonal phase identified as U3O7−z (c/a ≪ 1.032). U4O9 has not been detected in any sample. The Raman study carried out consists of both qualitative and quantitative analysis. The former, where a profile analysis has been performed on the acquired spectra, shows that the most intense bands (centered at ∼455 and ∼635 cm−1) are actually a doublet each, in agreement with a previous experimental study. Moreover, this work shows, for the first time, that the band at ∼160 cm−1 is also a doublet, which makes its classical assignment no longer obvious. The most important and original results from this study are obtained by applying Quantitative Raman Spectroscopy (QRS). This analysis shows that the second contribution at ∼475 cm−1 to the known T2g mode increases its relative intensity with the oxidation degree. This contribution may be related to the tetragonal distortion occurring in the cubic UO2 lattice due to the addition of interstitial oxygen, based on its comparison with the obtained XRD outcomes. In addition, the so-called "defects band" (centered at around 600 cm−1) presents a remarkable kink, of around 20 cm−1, in its Raman shift between UO2.26 and UO2.28. Such behavior might be directly associated with the observed appearance of the stoichiometric U3O7 phase (c/a = 1.032) for UO2.28 and UO2.30. [ABSTRACT FROM AUTHOR]

Acetohydroxamic acid (AHA) has been widely used in the development of reprocessing processes for spent nuclear fuel (SNF) due to its ability to form hydrophilic complexes preferentially with tetravalent metals and to contribute to the control of their oxidation states. It is also well known that AHA undergoes hydrolytic degradation under acidic conditions used during reprocessing. In spite of the wide variety of already published studies concerning the use of AHA, a further analysis of the effect of its hydrolysis on the metal complexing capacity of the extraction system is still needed. In this work we present a spectroscopic study (Raman and fluorescence emission) with the aim of analyzing not only the hydrolysis of AHA in the presence of europium (Eu), but also the effect of its degradation with regard to the global extraction system behavior. Particularly, we have focused on the actinides (An) stripping from lanthanides (Ln) in a EURO-GANEX process. To analyze these effects we have first measured the influence on the An/Ln separation factor. Then, the hydrolysis rate constant and Eu(III) fluorescence as a function of the AHA hydrolysis time have been evaluated to explain these effects. Our results show a decrease in DM(III) values that should be considered for all those studies of process development taking more than 24 hours. An increase in the Eu complexation in the aqueous phase as a function of time has also been observed, which is not directly associated with the formation of AHA hydrolysis products. This behavior predicts that AHA degradation could have an additional effect on the coordination of some Ln when it is employed for An/Ln separation. [ABSTRACT FROM AUTHOR]

Raman spectra of 1,2-ethylenediamine (EDA) in aqueous solutions are used to demonstrate that EDA molecules experience an anti–gauche conformational change resulting from the interactions with water. The observed Raman shift reveals a compressive (hydrophobic) effect of water on both methylene and amino groups of EDA. Raman spectra of EDA at high pressures are used as reference to quantify the intermolecular EDA–H2O interactions in terms of local pressures. These results are compared with macroscopic solvation pressures calculated from the cohesive energy parameter. We compare and discuss all our observations with available computational and experimental studies. [ABSTRACT FROM AUTHOR]

The study of uranium oxides at different conditions is of paramount importance in the nuclear field, especially regarding characterization of the spent nuclear fuel behavior in dry storage scenarios. This paper reports results of XRD and Raman analysis on four powdered samples prepared in order to cover a specific stoichiometry range in UO 2+ x , i.e. x = 0.24, 0.26, 0.28 and 0.30. XRD results reveal a clear increase of the average tetragonal distortion with the increase in oxidation degree, with the main phase detected for all the samples being a weakly tetragonal phase identified as U 3 O 7- z ( c / a ≪ 1.032). U 4 O 9 has not been detected in any sample. The Raman study carried out consists of both qualitative and quantitative analysis. The former, where a profile analysis has been performed on the acquired spectra, shows that the most intense bands (centered at ∼455 and ∼635 cm -1 ) are actually a doublet each, in agreement with a previous experimental study. Moreover, this work shows, for the first time, that the band at ∼160 cm -1 is also a doublet, which makes its classical assignment no longer obvious. The most important and original results from this study are obtained by applying Quantitative Raman Spectroscopy (QRS). This analysis shows that the second contribution at ∼475 cm -1 to the known T 2g mode increases its relative intensity with the oxidation degree. This contribution may be related to the tetragonal distortion occurring in the cubic UO 2 lattice due to the addition of interstitial oxygen, based on its comparison with the obtained XRD outcomes. In addition, the so-called "defects band" (centered at around 600 cm -1 ) presents a remarkable kink, of around 20 cm -1 , in its Raman shift between UO 2.26 and UO 2.28 . Such behavior might be directly associated with the observed appearance of the stoichiometric U 3 O 7 phase ( c / a = 1.032) for UO 2.28 and UO 2.30 .