Abstract
X-ray absorption spectroscopy was applied to understand the speciation of elements relevant to the immobilisation and disposal of radioactive plutonium bearing wastes, utilizing Ce as a Pu surrogate. Ce L3 XANES (X-ray Absorption Near Edge Structure) characterisation of a crystallised glass material produced by cold crucible plasma vitrification, at demonstration scale, evidenced incorporation as Ce3+ within the glass phase, providing an important validation of laboratory scale studies. U and Ce L3 XANES investigation of brannerite ceramics, U0.9Ce0.1Ti2O6, synthesized under oxidizing, neutral and reducing conditions, established the charge compensation mechanism as incorporation of Ce3+ through formation of U5+ and/or U6+ In each of these examples, X-ray Absorption Spectroscopy has provided a pivotal understanding of element speciation in relation to the mechanism of incorporation within the host wasteform intended for geological disposal.
Highlights
The UK is engaged in a programme of decommissioning, clean up and disposal of legacy facilities and materials from over five decades of nuclear fuel cycle activities
A tool box of thermal treatment technologies is under development for conditioning of plutonium / Mixed Oxide (MOX) residues and plutonium contaminated materials (PCM) wastes, as well as other complex higher activity wastes, which are incompatible with cement encapsulation [2,3,4,5,6,7,8,9,10,11,12,13]
The Ce L3 edge XANES data of slag wasteforms produced by cold crucible plasma vitrification, provide a useful and essential verification of Ce partitioning and reduction in a demonstration scale cold crucible processing, which was not sensitive to waste loading
Summary
The UK is engaged in a programme of decommissioning, clean up and disposal of legacy facilities and materials from over five decades of nuclear fuel cycle activities This programme will extend over more than 120 years and cost in excess of £115 billion [1]. Primary drivers for the application of thermal treatment processes include the reduced volume, improved passive safety, and superior long term stability of the waste form products [3]. These benefits arise from destruction of the organic waste fraction, oxidation of the metal waste component, and evaporation of entrained water, in tandem with the immobilisation of radioactive and chemotoxic elements within a durable ceramic, glass, or glass-ceramic material. The critical role of speciation, determined by X-ray Absorption Spectroscopy, in controlling the incorporation mechanisms, is emphasised
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