HIPed Pollucite Glass-Ceramics as Advanced Wasteforms for the Immobilization of Cs-Loaded IONSIV Wastes

A promising novel candidate glass-ceramic wasteform based on pollucite for the immobilization of Cs-loaded IONSIV^® with high Cs selectivity and retention has been developed. Inorganic ion exchangers have proven to be the most effective technology for sequestering radionuclides from liquid waste streams in the nuclear industry. The wasteform was designed to target pollucite, srilankite, and rutile phases where pollucite formation was a function of Cs loading on the IONSIV^®. This provides effective control over the phase formation as well as elimination of soluble Cs-rich phase(s) that may otherwise form during processing. The tailored pollucite glass-ceramic provides chemical and processing flexibility through the addition of small amounts of glass formers. Caesium was determined to be partitioned predominantly to the ceramic phase, thus taking advantage of pollucite’s relatively high chemical durability. Glass was included to provide chemical and processing flexibility and to increase the tolerance of the design to variations in Cs-loading on the IONSIV^®. Importantly, the wasteform design and tailored additives ensure the production of a consistent phase formation in the wasteform, irrespective of Cs-loading on the IONSIV^®.<br/><br/>Highly stable and durable wasteforms were produced via sintering and hot-isostatic pressing (HIP) with waste loadings of up to 70 – 80 wt.%. HIPing was employed to enhance the densification of the glass-ceramic and to ensure prevention of Cs-release <i>via</i> volatilisation to the off-gas during final consolidation within the HIP canister. The amount of glass in the formulation was further tailored to balance the processing benefits with the waste loading reduction. In addition, the properties of the HIPed wasteforms were compared with samples densified <i>via</i> sintering, to examine the impact of HIPing on its effectiveness for waste immobilisation.<br/><br/>The waste loading, extent of densification, phase stability of the wasteform, the HIP canister-wasteform interaction and aqueous durability of pollucite glass-ceramic wasteform were examined after densification <i>via</i> the HIPing process. The designed glass-ceramic wasteform provides an excellent wasteform candidate for permanent storage and final disposal of international Cs-loaded IONSIV^® wastes.