Effect of Ti-metal addition on hot-isostatically pressed (HIPed) Synroc-C

Synroc, a candidate nuclear wasteform and Synroc technology, a waste treatment solution utilizing hot-isostatic pressing (HIPing) have significant potential for the immobilisation of challenging nuclear wastes from both current and innovative reactors and fuel cycles. Hot isostatic press (HIP) consolidation is undertaken within sealed metal HIP canisters, where metal buffers (e.g., Ti, Fe and Ni) can be incorporated to control the redox environment within the canister. This study, for the first time, reports the effect of varying Ti-metal addition (0, 2, 4, and 8 wt.%) on phase formation, microstructural characteristics, and wasteform performance for HIP consolidated Synroc-C containing 20 wt.% simulated PUREX type (PW-4b) high level waste. Quantitative X-ray diffraction analysis, scanning electron microscopy-energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy-EDS analyses were undertaken for analytical investigations. The chemical durability of the samples was assessed using ASTM C1220-21 standard test. Hot-isostatically pressed (HIPed) samples with 0 and 8 wt.% Ti added for redox control produced unfavourable phase formation. However, the HIPed samples with Ti additions of 2 and 4 wt.% as a redox buffer showed the desired phase formation of Synroc-C without any significant change to the partitioning of waste elements among the phases along with compatible durability results, when compared to previous literature for hot uniaxial pressing (HUPed) or sintered materials.