A Feasibility Investigation of Laboratory Based X-ray Absorption Spectroscopy in Support of Nuclear Waste Management
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.44
A Feasibility Investigation of Laboratory Based X-ray Absorption Spectroscopy in Support of Nuclear Waste Management L.M. Mottram, M.C. Dixon Wilkins, L.R. Blackburn, T. Oulton, M.C. Stennett, S.K. Sun, C.L. Corkhill, and N.C. Hyatt Immobilisation Science Laboratory, University of Sheffield, Department of Materials Science and Engineering, Sir Robert Hadfield Building, Mappin Street, S13JD, UK
ABSTRACT
X-ray Absorption Spectroscopy is a technique of fundamental importance in nuclear waste management, as an element specific probe of speciation, which governs radionuclide solubility, immobilisation and migration. Here, we exploit recent developments in laboratory instrumentation for X-ray Absorption Spectroscopy, based on a Rowland circle geometry with a spherically bent crystal analyser, to demonstrate speciation in prototype ceramic and glass-ceramic waste forms. Laboratory and synchrotron XANES data acquired from the same materials, at the Ce and U L3 edges, were found to be in excellent quantitative agreement. We establish that analysable laboratory XANES data may be acquired, and interpreted for speciation, even from quite dilute absorber concentrations of a few mol%, albeit with data acquisition times of several hours. For materials with suitable absorber concentrations, this approach will enable routine element specific speciation studies to support rapid optimisation of radioactive waste forms and analysis of radiological materials in a purpose designed laboratory, without the risk associated with transport and manipulation at a synchrotron radiation facility.
INTRODUCTION As an element specific probe of speciation X-ray absorption spectroscopy (XAS) finds ubiquitous and powerful application in the field of nuclear waste management, in particular in the development of waste form materials 1-16. The fundamental requirement for a tunable broadband source of high brilliance X-rays, has, hitherto, generally required exploitation of synchrotron radiation sources for application of XAS techniques. However, recent advances in laboratory XAS instrumentation, exploiting spherically bent crystal analysers (SBCAs) in Rowland circle geometry, or bent cylindrical analysers in von Hamos geometry17-26. The use of SBCAs generally delivers higher spectral resolution 27
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in the region of the X-ray Absorption Near Edge Structure (XANES), but the requirement to work close to back scattering geometry requires several monochromator crystals to cover the range 5 – 18 keV, and a precision motor driven system to maintain optical alignment17-21. In contrast, the von Hamos geometry utilises only a single bent crystal analyser and does not necessarily require movement of components for acquisition of spectra, however, the achievable re
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