Opportunities and challenges of applying advanced X-ray spectroscopy to actinide and lanthanide N-donor ligand systems.

Tim Pruessmann,Peter Nagel,Robert Gordon,Tonya Vitova,David Batchelor,Laura Simonelli,Michael Trumm,Bernd Schimmelpfennig

doi:10.1107/s1600577521012091

Abstract

N-donor ligands such as n-Pr-BTP [2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine] preferentially bind trivalent actinides (An3+) over trivalent lanthanides (Ln3+) in liquid-liquid separation. However, the chemical and physical processes responsible for this selectivity are not yet well understood. Here, an explorative comparative X-ray spectroscopy and computational (L3-edge) study for the An/Ln L3-edge and the N K-edge of [An/Ln(n-Pr-BTP)3](NO3)3, [Ln(n-Pr-BTP)3](CF3SO3)3 and [Ln(n-Pr-BTP)3](ClO4)3 complexes is presented. High-resolution X-ray absorption near-edge structure (HR-XANES) L3-edge data reveal additional features in the pre- and post-edge range of the spectra that are investigated using the quantum chemical codes FEFF and FDMNES. X-ray Raman spectroscopy studies demonstrate the applicability of this novel technique for investigations of liquid samples of partitioning systems at the N K-edge.

Highlights

A way to significantly reduce the volume and the heat load of a repository after some decades and the long-term radiotoxicity of spent nuclear fuel is the so-called Partitioning and Transmutation (P&T) strategy (Magill et al, 2003; OECD, 2011; Salvatores & Palmiotti, 2011; Gonzalez-Romero, 2011)
The electronic and geometric structures of [An/Ln(n-PrBTP)3](NO3)3, [Ln(n-Pr-BTP)3](CF3SO3)3 and [Ln(n-PrBTP)3](ClO4)3 complexes are probed from the metal ‘pointof-view’ using An/Ln L3-edge HR-XANES and core-to-core resonant inelastic X-ray scattering (CC-RIXS) as well as HR-XANES ab initio quantum chemical calculations
The Ln/An L3-edge HR-XANES technique reveals higher charge density on the metal Ln/An atoms for the [Ln/An(n-PrBTP)3](OTf/NO3)3 compared with the Ln/An(OTf/NO3)3 complexes

Summary

Introduction

A way to significantly reduce the volume and the heat load of a repository after some decades and the long-term radiotoxicity of spent nuclear fuel is the so-called Partitioning and Transmutation (P&T) strategy (Magill et al, 2003; OECD, 2011; Salvatores & Palmiotti, 2011; Gonzalez-Romero, 2011). The different components are separated (partitioning) and the transuranium elements are converted to short-lived or stable nuclides (transmutation) using neutron-induced fission or capture reactions. A major step in P&T is the separation of 5f elements, especially the minor actinides (An), from their chemically similar 4f counterparts. This separation is necessary, as the lanthanide (Ln) fission products have large neutron absorption cross sections and thereby compromise transmutation efficiency in the nuclear fission process.

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