Abstract
With their high chemical and self-irradiation stability, crystalline monazites are among the most promising materials for the encapsulation of nuclear wastes. Yet, the local and magnetic structures of the matrices doped with low-content actinide cation, depicted as most resistant, are still unclear. This limits the development of theoretical approaches predicting their behavior under extreme conditions—self-irradiation and long-term leaching. Here, we characterize the model matrices La1–xMxPO4 (0 ≤ x ≤ 0.10)—with M = Sm, 239Pu, 241Am—by X-ray diffraction and solid-state 31P NMR. As an example, we confirm that La0.96241Am0.04PO4 has higher self-irradiation resistance compared to 241AmPO4. Further, computational analyses show that magnetic properties of the Pu complex are strongly affected by the J-mixing and the paramagnetic NMR shifts are dominated by the Fermi contact contribution, arising from delocalization of the spin density of the cation toward the phosphorus through the bonds.
Highlights
In most countries, the lead directives for managing nuclear wastes are through deep geological disposal in glasses, metals, and crystalline ceramics.[1]
The physical and chemical durability of phosphate monazites is proven by the discovery of a well-crystallized 2-billion-year-old sample;[2] their low alteration to leaching;[3] and their high self-healing capacity as the α-decay produced is sufficient to repair the structure damaged by the recoil nuclei.[4]
They were characterized by X-ray diffraction (XRD) and 31P Magic angle spinning (MAS)-NMR
Summary
The lead directives for managing nuclear wastes are through deep geological disposal in glasses, metals, and crystalline ceramics.[1]. While the long-range structure is probed by X-ray diffraction (XRD), due to the low actinide content, the understanding of the atomic scale structure remains unknown. Results on a series of La1−xPuxPO4 using PuLIII extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge spectroscopy (XANES) shows unclear outputs as the spectra were similar.[6] Magic angle spinning (MAS)-NMR is a good alternative for such atomic scale analyses as it is sensitive to order, disorder,[7] and probing low metal content.[8−10] With the unpaired 5f electrons, MAS-NMR has a powerful dual capability: structural and magnetic.
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