Investigation of transport processes of actinides by use of an analytical ultracentrifuge for optimizing the purex-process

Abstract

Transport data of Actinides in relevant solutions are urgently needed to optimize the electrochemical techniques introduced quite recently into the purex process. Therefore an Analytical Ultracentrifuge has been used for the determination of diffusion coefficients of Th(NO 3) 4, Pu(NO 3) 4, Np(NO 3) 4, NpO 2NO 3, NpO 2(NO 3) 2, PuO 2(NO 3) 2 and UO 2(NO 3) 2 in aqueous HNO 3 solutions and partially in TBP (30%) Dodecane-mixtures at 25 °C in the concentration range from 10 −2 M to 10 −1 M, applying Schlieren-, absorptions- and Rayleigh-Interference optics combined with laser techniques. In the Th(NO 3) 4–HNO 3–H 2O system which stood for the tetravalent actinides, it was shown that the apparent diffusion coefficient (D app = 5,8 X 10 −6 cm 2 s −1) equalled the main diffusion coefficient (D main = 6,3 X 10 −6 cm 2 s −1, proving that the cross term could be neglected. An analytical ultracentrifuge can also be used for investigating and determining the kinetics and distributions of extraction processes. Moreover diffusion coefficients of UO 2(NO 3) 2·2TBP in pure dodecane, pure TBP and TBP-dodecane mixtures (30%/70%) were determined within the concentration range from 5 × 10 −3 M to 5 × 10 −2 M. The obtained results plotted against concentration give straight lines. In pure dodecane the diffusion coefficient of UO 2(NO 3) 2·2TBP was found to be 3 × 10 −6 cm 2 s −1, this value decreasing for 10% by adding 30% TBP. The diffusion coefficients were compared with electrochemical transport data, obtained earlier from conductance and transference measurements, also with limiting ionic conductances of Am 3+ and Cm 3+, found quite recently.