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Abstract
Assessment of glass dissolution kinetics, under disposal relevant temperature and pH environments, is required to credibly estimate radionuclide release rates from vitrified radioactive waste. Leaching of the International Simple Glass (ISG) under acidic to hyperalkaline conditions was examined. Forward rate measurements have been obtained using the dynamic leaching SPFT protocol and rate parameters for B, Na and Si in the basic regime; errors in rates predicted using these parameters at high pH and temperature are significant because the fitting uses logarithmic data. Longer term behaviour under hyperalkaline conditions, representative of some disposal environments, was investigated using the PCT and MCC-1 static leaching protocols with Ca(OH)2 solutions for up to 120 days (PCT) and 720 days (MCC-1). In hyperalkaline conditions dissolution was incongruent for all elements and the presence of alternating zirconia-rich and zirconia-poor alteration layers was observed on all leached monoliths, indicating the occurrence of a self-organisation phenomenon during leaching.
Highlights
Radioactive waste produced from the reprocessing of spent nuclear fuel in the UK and other countries is immobilized in alkaliborosilicate glasses, and is destined for final disposal in a deep geological disposal facility (GDF)
Possible interactions of the vitrified high level waste (HLW) with a highly alkaline plume originating from the intermediate level waste (ILW) repository have to be taken into account
Understanding the leaching behaviour of vitrified waste glasses under the hyperalkaline conditions imposed by a cementitious environment is important for the development of the repository safety case
Summary
Radioactive waste produced from the reprocessing of spent nuclear fuel in the UK and other countries is immobilized in alkaliborosilicate glasses, and is destined for final disposal in a deep (typically >500 m) geological disposal facility (GDF). Providing that forward dissolution rates are measured in experiments performed over a range of temperature and pH values, the SPFT methodology enables the determination of the rate law parameters k0, Ea and η.
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