ISSUES AFFECTING THE PREDICTION OF GLASS REACTIVITY IN AN UNSATURATED ENVIRONMENT

Prior to the licensing of a high-level waste repository, the US Department of Energy (DOE) will seek to initiate hot startup of the high-level waste glass processing facilities at Savannah River and West Valley. To provide confidence that issues related to glass reactivity and disposal are evaluated prior to startup, the Environmental Restoration and Waste Management branch of DOE is studying important physical parameters that will affect glass reaction in a repository environment and is developing a modeling approach to predict glass performance. In this report, results are presented comparing the reactivity of fully radioactive glass with simulated glass of the same nominal composition. While differences in elemental releases between the glass types are observed, the differences are moderated with time and can be related to the dominant reaction mechanism. Additionally, the relationship between glass surface area and the volume of leachate (SA/V) is evaluated. The reactivity at different SA/V is dominated by solution pH and reaction affinity, with an increase in reactivity observed at long reaction times. Finally, data are presented which provide necessary parameters for the application of predictive modeling. In particular, forward reaction rate constants are presented, for a 165-frit based glass and a simple analogue, and a list of secondary phases observed during glass reaction under a variety of conditions is compiled.