Glass - Back to the Future!

Presenting Author:
M. T. Harrison

article posted 22 March

M. T. Harrison is a technical specialist with over 10 years experience in the vitrification of a wide range of radioactive waste streams, including HLW, ILW, plutonium and uranium. He is technical lead of vitrified wasteform performance activities, and has developed considerable knowledge of glass dissolution mechanisms and durability testing methodologies, including a wide range of ASTM standards. His work also includes glass formulation chemistry, vitrification processes and wasteform properties.

Product quality assessment of alternative glass formulations for vitrification of nuclear waste streams containing high concentrations of sodium

M. T. Harrison*1, C. J. Steele2, M. Cowley2, K. Ferguson2, C. T. Brigden3, R. J. Hand3
1 National Nuclear Laboratory, Sellafield, Seascale, Cumbria, CA20 1PG, UK 2 Sellafield Ltd, Sellafield, Seascale, Cumbria, CA20 1PG, UK 3 ISL, Department of Materials Science & Engineering, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD, UK

Sodium carbonate is currently being considered as a wash-out reagent for the removal of the settled solids in the unagitated Highly Active Liquor (HAL) storage tanks at Sellafield. As the settled solids are expected to comprise mainly zirconium molybdate (ZM), this will result in a feed to the Waste Vitrification Plant (WVP) containing high concentrations of both molybdenum and sodium. This feed is expected to be challenging for WVP due to solubility limitations in existing base glass compositions and the operating temperature. In particular, depending on the wash-out strategy employed, there is the potential to produce high volumes of sodium-containing waste, which will result in large quantities of vitrified HLW containers. Hence, new glass compositions are being investigated in order to maximise the sodium content of the vitrified product and minimise the number of containers produced. This paper describes the product quality assessment of two candidates that have been investigated to date; namely sodium aluminium phosphate and sodium titanosilicate. These two glasses can potentially contain up to 25 wt% Na2O, more than doubling that possible in existing borosilicate compositions.