Browsing by Author "Maddrell, ER"

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    Flexible process options for the immobilisation of residues and wastes containing plutonium
    (American Society of Mechanical Engineers (ASME), 2007-09-02) Stewart, MWA; Moricca, SA; Begg, BD; Day, RA; Scales, CR; Maddrell, ER; Eilbeck, AB
    Residues and waste streams containing plutonium present unique technical, safety, regulatory, security, and sociopolitical challenges. In the UK these streams range from lightly plutonium contaminated materials (PCM) through to residues resulting directly from Pu processing operations. In addition there are potentially stocks of Pu oxide powders whose future designation may be either a waste or an asset, due to their levels of contamination making their reuse uneconomic, or to changes in nuclear policy. While waste management routes exist for PCM, an immobilisation process is required for streams containing higher levels of Pu. Such a process is being developed by Nexia Solutions and ANSTO to treat and immobilise Pu waste and residues currently stored on the Sellafield site. The characteristics of these Pu waste streams are highly variable. The physical form of the Pu waste ranges from liquids, sludges, powders/granules, to solid components (e.g., test fuels), with the Pu present as an ion in solution, as a salt, metal, oxide or other compound. The chemistry of the Pu waste streams also varies considerably with a variety of impurities present in many waste streams. Furthermore, with fissile isotopes present, criticality is an issue during operations and in the store or repository. Safeguards and security concerns must be assessed and controlled. The process under development, by using a combination of tailored waste form chemistry combined with flexible process technology aims to develop a process line to handle a broad range of Pu waste streams. It aims to be capable of dealing with not only current arisings but those anticipated to arise as a result of future operations or policy changes.
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    Silver iodide sodalite for 129I immobilisation
    (Elsevier B.V., 2016-11-01) Vance, ER; Gregg, DJ; Grant, C; Stopic, A; Maddrell, ER
    Silver iodide sodalite was initially synthesised as a fine-grained major phase in a nominally stoichiometric composition following hot isostatic pressing at 850 °C with 100 MPa and its composition, Ag4Al3Si3O12I, was approximately verified by scanning electron microscopy. An alternative preparative method yielded a more dense and stoichiometric AgI sodalite on sintering and HIPing. As found for AgI, the I is released from AgI sodalite much more readily in reducing water than in ordinary water. Thus in normal PCT-B tests, the I release was <0.3 g/L in water, but it was ∼70 g/L under highly reducing conditions. This is an important point with regard to can material if HIPing is used for consolidation. © 2016 Elsevier B.V.
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    Silver iodide sodalite – wasteform / HIP canister interactions and aqueous durability
    (Elsevier, 2019-04-15) Maddrell, ER; Vance, ER; Grant, C; Aly, Z; Stopic, A; Palmer, T; Harrison, JJ; Gregg, DJ
    The use of silver zeolite for the capture of radioiodine from the vapour phase, followed by thermal conversion now appears to be the most direct route by which a sodalite wasteform can be formed. In addition, consolidation by hot-isostatic pressing (HIP) in sealed canisters has many significant advantages over conventional methods such as sintering or melting these candidate wasteforms. The choice of HIP canister material is important as reaction at the wasteform/HIP canister interface results in an interaction zone that can potentially produce detrimental phases, wasteform porosity and canister thinning. This paper builds on a previous study that demonstrated that iodine could be captured from the vapour phase using silver exchanged zeolite and converted to sodalite by HIPing in Fe HIP canisters. The Cu or Ni metal HIP canisters used in this work result in an ∼100–200 μm thick local interaction zone with a variety of chemistries. Durability studies were conducted using a variety of reducing conditions and clearly demonstrated the redox sensitivity of silver sodalite. While the silver sodalite wasteform produced is, like the popular AgI-based wasteforms, highly leach resistant to leaching by deionised water it was unstable under highly reducing conditions, which are likely to occur in most geological disposal facilities. Post leaching characterisation revealed the redeposition of AgI and the formation of an aluminosilicate alteration layer under some leaching conditions. Appropriate precautions are required should a silver sodalite wasteform for iodine immobilisation be exposed to reducing groundwater conditions. Crown Copyright © 2019 Published by Elsevier B.V.