Browsing by Author "Grant, C"

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    Immobilization of iodine via copper iodide
    (Elsevier, 2018-07) Vance, ER; Grant, C; Karatchevtseva, I; Aly, Z; Stopic, A; Harrison, JJ; Thorogood, GJ; Wong, HKY; Gregg, DJ
    CuI is a candidate wasteform for the immobilization of the fission product 129I. CuI can be made simply by the addition of CuCl to an I− bearing solution such that exchange of Cl− with I− takes place. The CuI material can then be consolidated into a wasteform by sintering at approximately 550 °C in argon or by hot isostatically pressing at 550 °C with 100 MPa of pressure. A waste loading of greater than 60 wt.% is achievable with good water leach resistance, in keeping with the low solubility product of CuI. However, like the well known wasteform candidate AgI, CuI decomposes in water containing metallic Fe. To compensate this deficiency, the sintered CuI wasteform can be further protected by surrounding it by Sn powder and HIPing at the low temperature of 200 °C. © 2018 Elsevier B.V
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    Incorporation of Ba in Al and Fe pollucite
    (Elsevier B.V., 2016-09-01) Vance, ER; Gregg, DJ; Griffiths, GJ; Gaugliardo, PR; Grant, C
    Ba, the transmutation product of radioactive Cs, can be incorporated at levels of up to ∼0.07 formula units in Cs(1−2x)BaxAlSi2O6 aluminium pollucite formed by sol-gel methods and sintering at 1400 °C, with more Ba forming BaAl2Si2O8 phases. The effect of Ba substitution in pollucite-structured CsFeSi2O6 was also studied and no evidence of Ba substitution in the pollucite structure via cation vacancies or Fe2+ formation was obtained. The Ba entered a Fe-silicate glass structure. Charge compensation was also attempted with a Cs+ + Fe3+ ↔ Ba2+ + Ni2+ scheme but again the Ba formed a glass and NiO was evident. PCT leaching data showed CsFeSi2O6 to be very leach resistant. © 2016 Elsevier B.V.
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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.