article posted 18 March 2016
Daniel Backhouse completed a Master’s degree in Physics at the University of Warwick before beginning a PhD
in high-pH dissolution of nuclear waste glasses in 2012, under the supervision of Prof Russell Hand, Dr Claire Corkhill, Prof Neil Hyatt
and Dr Mike Harrison. His work has involved investigating the dissolution behaviour of current and proposed nuclear waste glasses, as well
as investigating the roles of specific elements, such as Ca and Mg, in affecting this
Is the International Simple Glass a Valid Analogue for the Dissolution of UK High-Level Waste Glass at High-pH?
Daniel J. Backhouse*1, Claire L. Corkhill1, Mike T. Harrison2, Neil C. Hyatt1 and Russell J. Hand1.
1Immobilisation Science Laboratory, Department of Materials Science and Engineering, University of Sheffield, Sheffield, S1 3JD
2National Nuclear Laboratory, Central Laboratory, Sellafield, Seascale, Cumbria, CA20 1PG
n accurate picture of the dissolution behaviour of UK High-Level Waste (HLW) glass is a vital part of the safety case for the disposal of HLW
in a Geological Disposal Facility (GDF). However, due to a number of factors, including the wide array of different nuclides that glasses can
incorporate within their structure, the mechanisms of nuclear waste glass dissolution are not thoroughly understood. As part of an initiative to
address this, the International Simple Glass (ISG) was designed . The composition is that of a boroaluminosilicate glass, containing elements
consistent with those in the nuclear waste glasses of a number of countries, including the US and France. The composition of some of the UK’s
HLW glass is quite different to this, containing, for example, signficant amounts of Mg and Fe, both of which are known to affect glass dissolution [2,3].
We present the results of long-term durability experiments conducted on MW-25%, a waste-loaded simulant of UK HLW vitrified product, and ISG.
Experiments were carried out utilising both the MCC-1 (up to 720 days duration) and PCT-B (up to 112 days) protocols, at 50 °C in saturated Ca(OH)2
11.6), in order to model the potential situation of a highly-alkaline plume within the GDF. Normalised mass losses were calculated from ICP-OES analysis
of the leachates. Alteration layers and crystalline precipitates were observed for each glass at each time interval, the structures and compositions of which are
detailed here through analysis by SEM-EDS, TEM with electron diffraction, micro-focus XRD and geochemical modelling using PHREEQC. We compare the dissolution
behaviour of the two glasses, and highlight the issues which suggest that ISG is not a valid analogue for the dissolution of UK HLW glass in high-pH environments.
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