Nuclear waste streams consist of a diversity of physical and chemical forms, requiring a toolbox approach in the application of materials to their disposal. Solid uranium metal wastes constitute a disposal challenge due to their tendency to oxidise, making encapsulation within cementitious waste packages for storage potentially troublesome. MKPC (Magnesium Potassium Phosphate Cement) is being considered as an alternative to Portland cement for U-metal encapsulation due to the potential for lower free water content, lower internal pH and the micro-encapsulation of radioactive isotopes as low-solubility phosphate minerals. In this work the development and characterisation of MKPCs optimised for U-metal encapsulation was undertaken. This included the investigation of MKPC property development under both near ambient and elevated temperature conditions, the performance of MKPC/U-metal wasteform corrosion trials utilising temperature elevation (to 30, 40 and 50 °C) for the acceleration of chemical kinetics, and assessment of the impact of dehydration treatments (at 50, 80 and 110 °C) on the cement properties. In general MKPC exhibited excellent processing and mechanical properties. Other significant outcomes of the work include, firstly, the determination that uranium corrosion rate dependencies in MKPC are dominated heavily by the presence of water over other chemical effects, with an anoxic activation energy of 68 ± 6 kJ/mol. Secondly, the development of a methodology for determining the bound water content of MKPC, which allowed the calculation of the extent of reaction. This enabled analysis yielding empirical strength-porosity and kinetic models of the material, capable of facilitating improved mix design for the tailoring of MKPC properties. Finally, the instability of the K-struvite matrix toward dehydration at temperatures of ≥ 72 °C has been recorded. The work concluded that MKPC has many properties which make it suitable as a general encapsulant, whilst being ultimately unsuitable for U-metal storage without further development around the reduction of water availability.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:702765 |
| Date | January 2014 |
| Creators | Montague, William |
| Contributors | Vandeperre, Luc |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/44117 |
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