Glass - Back to the Future!

Presenting Author:
Sean T. Barlow

article posted 21 March 2016/em>

Sean T. Barlow is a second year PhD research student at the University of Sheffields Immobilisation Science Laboratory and Nuclear Fission Research Science and Technology Doctoral Training Course. In 2013 Sean graduated from the University of Salford with an Honours degree in physics and is currently researching the safe immobilisation and encapsulation of damaged and corroded nuclear fuel residues.

Glass formulations for Magnox sludge immobilisation

Sean T. Barlow1*, Martin C. Stennett1, Russell J. Hand1, Sean P. Morgan2 & Neil C. Hyatt1
1 Department of Materials Science & Engineering, The University of Sheffield, Sheffield S1 3JD, UK 2 Sellafield Ltd., Hinton House, Risley, Warrington WA3 6GR, UK

This project investigates thermal treatment options for sludge wastes arising from long term storage of Magnox fuel elements under aqueous conditions. Two bounding extremes for the waste found within the First Generation Magnox Storage Ponds were proposed, one with 90% corroded Magnox cladding and 10% metallic content and the other 80% metallic content and 20% corroded Magnox cladding. Surrogates, neodymium metal and mischmetal (CeLaPrNd mixed metals) were used alongside uranium metal to assess their suitability in glass formulation studies. Glasses based on magnesium borosilicate and magnesium aluminosilicate systems were prepared doped with the simulant wastes. XRD and SEM-EDX identified UO2 (Figure 1.), U3O8, NdB6 & Nd0.3Ce0.7O1.85 crystal phases in the bulk glass. The U oxidation state for each sample was confirmed by XANES analysis (Figure 2.). All samples containing the low metallic waste stream melted homogeneously forming an X-ray amorphous material. Volume reduction achieved by vitrification was between 59% and 75%. DTA was performed for all samples identifying glass transition (670C, borosilicate glass; 630C, aluminosilicate glass), crystallisation points (between 700C and 1000C) and melting temperatures (~1150C, borosilicate glass; ~1400C, aluminosilicate glass). Dissolution studies of the U and Nd samples showed leach rates of boron =14 g/m2/d in the aluminosilicate glasses and =8 g/m2/d in the borosilicate glasses. Normalised mass loss of Nd did not exceed 0.01 gm-2 whilst U release was =1.3 gm-2. All samples were found to be at least as chemically durable as UK high level waste glass in terms of boron release rates over the 28 day accelerated leaching experiments.