Abstract
EELS based on features of ELNES of M 4 and M 5 edges can provide information regarding oxidation states of Ce and U in proposed host phases of radioactive wastes (e.g., pyrochlore, uraninite, and zirconolite). M 4 and M 5 edges of Ce 4+ have higher energy-loss than those of Ce 3+. Intensity ratio between M 4 and M 5 edges and weak peaks after the M 4 and M 5 edges can be used for quantification of Ce 3+ and Ce 4+. EELS results from an unaltered area of pyrochlore from Inner Mongolia of China shows Ce 3+ and other rare earth (RE) elements. However, EELS spectrum from the neighboring altered area shows Ce 4+, Ba and other RE elements. The oxidation of Ce results in loss of RE elements, U, and daughter product of α-decay, Pb during the alteration of the pyrochlore. However, most RE elements were incorporated in to alteration product, the Ce 4+-bearing pyrochlore. EELS spectra from a partially α-recoil damaged uraninite show that the ratio of U 6+/U 4+ is about 2/3. The alteration of uraninite and spent fuel (UO 2) in relatively reducing geological fluid results in the formation of coffinite that is a stable secondary waste form at low temperature.
Published Version
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