Abstract
Glass-ceramics with high glass fractions (70 wt%) were fabricated in stainless steel canisters by hot isostatic pressing (HIP), at laboratory scale. High (600 °C) and low (300 °C) temperature pre-treatments were investigated to reduce the canister evacuation time and to understand the effect on the phase assemblage and microstructure of the hot isostatically pressed product. Characterisation of the HIPed materials was performed using scanning electron microscopy (SEM), coupled with energy dispersive X-ray analysis (EDX) and powder X-ray diffraction (XRD). This analysis showed the microstructure and phase assemblage was independent of the variation in pre-treatment parameters. It was demonstrated that a high temperature pre-treatment of batch reagents, prior to the HIP cycle, is beneficial when using oxide precursors, in order to remove volatiles and achieve high quality dense materials. Sample throughput can be increased significantly by utilising a high temperature ex-situ calcination prior to the HIP cycle. Investigation of glass-ceramic wasteform processing utilising a glass frit precursor, produced a phase assemblage and microstructure comparable to that obtained using oxide precursors. The use of a glass frit precursor should allow optimised throughput of waste packages in a production facility, avoiding the need for a calcination pre-treatment required to remove volatiles from oxide precursors.
Highlights
Hot Isostatic Pressing (HIPing) is a process which simultaneously applies heat and pressure to consolidate and sinter materials
With the aim to improve sample throughput whilst maintaining sample quality and reproducibility, we investigated the use of a waste/precursor ex-situ calcination step as an alternative or supplement to the in-canister bake-out on laboratory scale 30 ml canisters
Powder X-ray diffraction (XRD) of the raw batch material before and after the overnight calcination was performed to characterise any significant changes to the raw reagents during either of the exsitu calcination or in-canister bake-out high temperature pretreatments
Summary
Hot Isostatic Pressing (HIPing) is a process which simultaneously applies heat and pressure to consolidate and sinter materials. The use of isostatic pressure during consolidation, applied using an inert gas, promotes densification, eliminating internal porosity. The UK's Nuclear Decommissioning Authority (NDA) has identified HIP as a potential method for treating plutonium residues at the Sellafield site [1,2]. Aside from the potentially reusable plutonium stockpile, approximately 0.5 tonnes of material is not economically viable for reuse and has been identified as waste [4]. These Pu-residues are classified as higher activity waste due to the Pu content exceeding that of plutonium contaminated material wastes
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