Glass - Back to the Future!

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article posted 20 june 2016

Clive Brigden I am an inorganic chemist with particular experience in glass and ceramic synthesis and characterisation. I am currently working on the immobilisation of POCO waste.

Titanosilicate glasses for the immobilisation of high soda wastes

Clive Brigden*,1, Russell Hand1, Lisa Hollands1, Mike Harrison2, Cath Stephen2, Tracey Taylor2, Michelle Cowley3, Katy Spencer3, Carl Steele3, John Longmore4 & Rowan Patel4
1ISL, Department of Materials Science & Engineering, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD, UK
2National Nuclear Laboratory, Sellafield, Seascale, Cumbria, CA20 1PG, UK
3Sellafield Ltd, Sellafield, Seascale, Cumbria, CA20 1PG, UK
4Cera Dynamics, Fountain Street, Fenton, Stoke-on-Trent, ST4 2HB, UK

One option for the post-operational clean-out of highly active storage tanks at Sellafield will result in a high soda-content waste stream that will also contain significant amounts of molybdenum and zirconium. Current base glasses used for the vitrification of nuclear waste in the UK contain significant amounts of soda and lithia which imposes a relatively low loading limit for such a waste with high soda and molybdenum contents. As part of a project to develop alternative glasses which could accommodate higher loadings of these wastes, thus reducing the number of final waste packages, we are investigating titanosilicate glasses which are known to accommodate high levels of soda.

The introduction of a simplified POCO waste of molybdenum oxide and zirconia into a series of sodium titanosilicate glasses with up to 10 mol% alumina and/or boron oxide has been investigated. The effects on waste uptake of introducing different components (including mixed alkali oxides, calcium oxide and boron oxide) into the base glass compositions have been examined.

In addition, work has been carried out into the synthesis of base glasses, including melting at a larger scale, without waste and with reduced soda contents (to allow for soda which would be supplied by the waste). Initial results including the identification of any crystalline phases formed using X-ray diffraction analysis and quantification of the extent of any phase separation observed is reported.

Results so far indicate that the introduction of boron oxide into the glass composition shows the most promise, a significant reduction in phase separation is observed and a lowering effect upon melt temperature.

Preliminary hydrothermal durability trials have begun and these will be reported as well as characterisation of the most promising samples.

In addition to establishing glass durability remaining challenges also include quantification and the reduction or elimination of any sodium molybdate phase present in the glass and to determine the extent to which soda can be removed from the base glass formulation and still produce a viable glass.

This document has been prepared by Clive Brigden as part of collaborative project involving Sellafield Ltd. Some of the information it contains is owned by Sellafield Ltd or NDA and is, or may be, proprietary or subject to restrictions relating to national security, commercial or personal obligations. It is submitted to Society of Glass Technology Centenary Conference 2016 for the purposes of professional assessment. It may be copied and distributed as required for this purpose but no other use may be made of any component owned by Sellafield Ltd or NDA without the prior permission of Sellafield Ltd.