Hot Isostatic Pressing—A Potential Thermal Treatment Process for Pu Immobilisation

Hot Isostatic Pressing (HIPing) is a batch thermal treatment process where wastes are heated and compressed within a sealed container under controlled conditions. This results in consolidated high density wasteforms with minimal loss of volatile elements and easy accountability of active inventory [1]. In the UK, HIPing was highlighted as one of the credible options for plutonium immobilisation in the event that disposal is chosen as a management strategy [2]. To help inform the science underpinning larger-scale industrial applications of this technology, the University of Sheffield have a small-scale HIP facility capable of processing radiological simulant wasteforms using an active furnace isolation chamber (AFIC) [3]. The AFIC is designed to function within a conventional HIP set up and provides a novel opportunity in the UK to fabricate and characterise conceptual radioactive wasteforms and gain experience with radiological HIPing. It was under this remit that HIP wasteforms were fabricated as part of a broad research portfolio targeting zirconolite (CaZrTi₂O₇) as a single host ceramic wasteform. These trials investigated the bulk phase assemblage and HIP canister-ceramic interactions with a range of potential charge compensation cations (Al³⁺, Fe³⁺, Mg²⁺). Comparison was made with wasteforms produced using typical sintering methods, for which, semi-dynamic static dissolution was performed to understand zirconolite durability. Overall, both HIPing and conventional sintering were determined to yield robust and durable zirconolite ceramic wasteforms across a range of compositions.<br/><br/>[1] M.W.A. Stewart, S.A. Moricca, T. Eddowes, Y. Zhang, E.R. Vance, G.R. Lumpkin, M.L. Carter, M. Dowson, M. James, The use of hot-isostatic pressing to process nuclear waste forms, Proceedings of the 2009 12^th International Conference on Environmental Remediation and Radioactive Waste Management ICEM2009, Liverpool, UK, 2009, pp. ICEM2009-16253.<br/>[2] Nuclear Decommissioning Authority, Progress on plutonium consolidation, storage and disposition 2019.<br/>[3] S.A. Moricca, R. Persaud, Active Furnace Isolation Chamber, WO 2018/009782 A1, 2018. &lt;!--![endif]----&gt;