Abstract
AbstractThe first comprehensive assessment of the dissolution kinetics of simulant Magnox–ThORP blended UK high-level waste glass, obtained by performing a range of single-pass flow-through experiments, is reported here. Inherent forward rates of glass dissolution were determined over a temperature range of 23 to 70°C and an alkaline pH range of 8.0 to 12.0. Linear regression techniques were applied to the TST kinetic rate law to obtain fundamental parameters necessary to model the dissolution kinetics of UK high-level waste glass (the activation energy (Ea), pH power law coefficient (η) and the intrinsic rate constant (k0)), which is of importance to the post-closure safety case for the geological disposal of vitreous products. The activation energies based on B release ranged from 55 ± 3 to 83 ± 9 kJ mol–1, indicating that Magnox–THORP blend glass dissolution has a surface-controlled mechanism, similar to that of other high-level waste simulant glass compositions such as the French SON68 and LAW in the US. Forward dissolution rates, based on Si, B and Na release, suggested that the dissolution mechanism under dilute conditions, and pH and temperature ranges of this study, was not sensitive to composition as defined by HLW-incorporation rate.
Highlights
TO predict the performance of nuclear waste glasses in a geological disposal facility (GDF), an understanding of the glass dissolution rate, in the context of the geochemical settings, is required
As it is understood that using the highest possible q/S value eliminates the potential effects of temperature increase on the dissolution rate (McGrail et al, 1997), a log10 (q/S) value of –6.5 ± 10% m s–1 was selected to determine the forward rate of dissolution for both MT25 and MT30 blend glasses
We report the first comprehensive study of the dissolution kinetics of simulant UK Magnox– ThORP blended high-level waste (HLW) glasses over a range of temperatures and alkaline pH regimes, including an investigation of the effect of altering glass composition on dissolution rate
Summary
TO predict the performance of nuclear waste glasses in a geological disposal facility (GDF), an understanding of the glass dissolution rate, in the context of the geochemical settings, is required. Flow-through approaches, including single-pass flow-through (SPFT) and micro-channel flow-through (MCFT) methodologies, are considered most appropriate to determine the reaction kinetics of glass dissolution (McGrail and Peeler, 1995). The continual introduction of fresh reaction media in the ‘flow-through’ methodology ensures that conditions are dilute, which is necessary to prevent the accumulation of reaction products. This maintains the chemical affinity term, Q/K, at near zero so that the inherent ‘forward rate’ of dissolution is sustained and experimental parameters such as temperature and pH can be varied to yield an accurate quantitative description of their impact on dissolution kinetics
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