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Abstract
Abstract
Radioactive waste streams that include metallic uranium are incompatible with conventional ordinary Portland cement (OPC)-based encapsulation matrices. These encapsulation systems are essentially composite materials that incorporate high replacement levels of pulverised fly ash (PFA) or blast furnace slag (BFS). A potential alternative encapsulant for the treatment of problematic waste streams is magnesium phosphate cement. This paper discusses the fundamental characterisation results obtained from two magnesium phosphate cement formulations being developed in the UK for the encapsulation of metallic intermediate level waste (ILW). When compared to conventional OPC based systems, the two magnesium phosphate cement formulations investigated have lower pH, are able to chemically combine more mix water into the system and provide sufficient workability at water/solid ratios close to the theoretical confines needed for paste saturation. The results presented have confirmed compliance of this material against NDA RWMD guidelines for strength and expansion. The X-ray diffraction (XRD) and differential scanning calorimetry (DSC) results obtained for both formulations up to 360 days cure time have indicated that the cement system shows evidence of chemical stability.
Thanks are given to the Immobilisation Science Laboratory at the University of Sheffield and AMEC Nuclear UK Ltd for funding. The authors are grateful to AMEC Nuclear UK Ltd for facilitating a long term placement in their laboratories, where the research was undertaken. The authors gratefully acknowledge Engineering and Physical Sciences Research Council for provision of an EngD studentship to the corresponding author, through the Nuclear Engineering Industrial Doctorate Centre.
Notes
This paper is part of a special issue on Cement and Concrete Science