EXAFS and XANES Analysis of Plutonium and Cerium Edges From Titanate Ceramics for Fissile Materials Disposal

Abstract

We report extended x-ray absorption fine structure (EXAFS) spectra from the plutonium LIII edge and x-ray absorption near edge structure (XANES) from the cerium LII edge and plutonium LIII edge in prototype titanate ceramic hosts. The titanate ceramics studied are based upon the hafnium-pyrochlore and zirconolite mineral structures that will serve as an immobilization host for surplus fissile materials. Our samples approximate the composition envelope expected for production materials, which will contain as much as 10.5 weight % fissile plutonium and 21 weight % (natural or depleted) uranium. Three ceramic formulations were studied: one employed cerium as a “surrogate” element, replacing both plutonium and uranium in the ceramic matrix, another formulation contained plutonium in a “baseline” ceramic formulation, and a third contained plutonium in a formulation representing a high-impurity plutonium stream. The cerium XANES from the surrogate ceramic clearly indicates a mixed IIIIV oxidation state for the cerium. In contrast, XANES analysis of the two plutonium-bearing ceramics shows that the plutonium is present almost entirely as Pu(IV) and occupies the calcium site in the zirconolite and pyrochlore phases. The plutonium EXAFS real-space structure shows a strong second-shell peak, clearly distinct from that of PuO2, with remarkably little difference in the plutonium crystal chemistry indicated between the baseline and high-impurity formulations

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Correspondence to J. A. Fortner.

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Fortner, J.A., Kropf, A.J., Bakel, A.J. et al. EXAFS and XANES Analysis of Plutonium and Cerium Edges From Titanate Ceramics for Fissile Materials Disposal. MRS Online Proceedings Library 608, 401 (1999). https://doi.org/10.1557/PROC-608-401

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