Brannerite glass ceramic wasteforms for immobilisation of nuclear fuel residues.

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This project seeks to address the requirement for treating damaged and degraded nuclear fuel materials present on the Sellafield site, immobilising these highly radioactive wastes in a glass-ceramic wasteform suitable for long term storage and final disposal. These materials range from wet sludges to dry granular materials. At present, there is no accepted waste treatment route or this material.We propose to develop a suite of novel glass-ceramic wasteforms for this purpose, based on synthetic brannerite, UTi2O6. The fuel residues are principally 96% UO2, with 3% fission products and 1% plutonium dissolved as a solid solution. It has been shown that geochemically altered natural mineral brannerites retain their uranium inventory for hundreds of millions of years, even after radiation induced amorphisation by alpha-decay. Natural brannerites have been shown to incorporate up to 4 wt% water, providing confidence that a synthetic brannerite wasteform will be compatible with processing of wet fuel residues. This project will design and develop develop glass-ceramic brannerite wasteforms, in which the highly durable brannerite ceramic phase, based on UTi2O6, incorporates long lived U and Pu, with a less durable glass phase to incorporate the short lived fission products.These ceramic wasteforms will be fabricated using the unique Hot Isostatic Pressing (HIP) facility for radiological materials, at the University of Sheffield. Materials will be characterised by X-ray diffraction, electron microscopy with X-ray analysis, Raman spectroscopy, pycnometry,thermal analysis, and U L3 edge X-ray Absorption Spectroscopy (collaboration with Brookhaven National Laboratory).