Browsing by Author "Stewart, MWA"

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    Alternative Synroc formulations
    (Cambridge University Press/Springer Nature, 2011-02-25) Vance, ER; Smith, KL; Thorogood, GJ; Begg, BD; Moricca, SA; Angel, PJ; Stewart, MWA; Ball, CJ
    Perovskite is the least durable of the resistate minerals comprising Synroc-C and it is desirable to reduce its abundance in Synroc. Kinetic limitations and competition with Csapparently affect the incorporation of Sr into hollandite during hot-pressing at 1200°C/20 MPa so that ~ 10% of perovskite (a value below the percolation limit) is probably an optimum target. Zirconolite-rich Synroc formulations have been prepared for actinide-rich wastes. Background XRD and TEM studies have also been performed to study the crystal-chemical behaviour of Nd (a simulant of trivalent actinides) in zirconolite. Either rare-earth compensated perovskite or freudenbergite in Synroc can evidently be used to immobilise Na-bearing HLW. © 1992 Materials Research Society
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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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    Interim report task 3: immobilisation process/equipment testing – task 3.4: nondestructive evaluation Part 1 of 2 to Lawrence Livermore National Laboratory for contract B345772
    (US Department of Energy (DOE), 2000-04-10) Stewart, MWA; Vance, ER; Day, RA; Lumpkin, GR
    This report contains a summary of the results generated for Task 3.4: Non-destructive Evaluation (a subtask of Task 3: Immobilization Process/Equipment Testing). The aim of this task was to carry out X-ray diffraction (XRD) on selected samples from previous Task 1: Form Development work. These XRD results were to be compared to the results obtained using quantitative scanning electron microscopy.
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    The role of titanate ceramics in immobilisation of wastes arising from partitioning and weapons disposition
    (Japan Atomic Energy Research Institute (JAERI), 2002-03-01) Hart, KP; Zhang, YJ; Begg, BD; Aly, Z; Brownscombe, AJ; Day, RA; Stewart, MWA; Lumpkin, GR; Vance, ER; Jotsons, A
    The development of ceramics for the immobilisation of radioactive wastes has been on-going at ANSTO since 1980 and has involved collaboration with JAERI, the USDOE, LLNL and other international laboratories. This work has examined various processing routes, radiation damage effects and long-term aqueous durability for a range of titanate ceramics. Within these studies, information on the long-term behaviour of ceramics chosen to immobilities excess Pu and actinide-rich wastes arising from partitioning strategies have been obtained. Overall, the long-term durability, limitations on criticality under processing and disposal conditions and existence of viable natural analogues endorse the use of titanate ceramics for immobilisation of actinide-rich wastes. © 2002 Japan Atomic Energy Research Institute
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    Safe immobilization of high-level radioactive waste in waste forms for geological repositories
    (Elsevier, 2011-10) Vance, ER; Stewart, MWA; Moricca, SA; Lumpkin, GR; Begg, BD
    The idea that spent fuel and other hazardous radioactive high-level wastes (HLW) would need to be dealt with arose soon after the first experimental demonstration of nuclear reactors in 1942. HLW is spent nuclear power plant fuel or waste deriving directly from reprocessing or recycling of spent fuel. This latter waste consists of mainly fission products (FPs), as well as minor actinides such as Np, Pu, Am and Cm. Table 1 shows the main components and relevant half-lives of reprocessing waste from the well-known Purex process. Also, there are abundant wastes from the production of Pu for nuclear weapons, mainly in the US and Russia. These wastes (Table 2), although designated as HLW in the US, have only around 0.1- 1% of the radioactivity per unit volume of the Purex-type HLW, and if they were located in most other countries would be categorised as intermediate-level waste (ILW). Current HLW inventories around the world run into tens of millions of tonnes. The manageability of HLW impacts directly on the sustainability of nuclear power. © 2011 Elsevier Ltd.
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    Zirconolite-rich titanate ceramics for immobilisation of actinides - waste form/HIP can interactions and chemical durability
    (Elsevier, 2009-12) Zhang, YJ; Stewart, MWA; Li, HJ; Carter, ML; Vance, ER; Moricca, SA
    Zirconolite-based titanate ceramics containing U plus Th or Pu have been prepared. The final consolidation to produce a dense monolithic waste form was carried out using hot isostatic pressing (HIPing) of the calcined materials within a stainless steel can. The ceramics were characterised and tested for their overall feasibility to immobilise impure Pu or separated actinide-rich radioactive wastes. As designed, tetravalent U and Pu are mainly incorporated in a durable zirconolite phase, together with Gd or Hf added as neutron absorbers. The interaction of the waste form with the HIP can was also examined. No changes in the U valences or the U/Pu-bearing phase distributions were observed at the waste form–HIP can interface. © 2009, Elsevier Ltd.