Waste Form Release Calculations for Performance Assessment of the Hanford Immobilized Low-Activity Waste Disposal Facility Using a Parallel, Coupled Unsaturated Flow and Reactive Transport Simulator

摘要

A set of reactive chemical transport calculations was conducted with the Subsurface Transport Over Reactive Multi-phases (STORM) code to evaluate the long-term performance of a representative low-activity waste glass in a shallow subsurface disposal system located on the Hanford Site. Technetium, the main contributor to a drinking water dose, is assumed to be released congruently with the dissolution of the glass. Sodium is released at a higher rate via a kinetic ion-exchange reaction. Aqueous equilibrium reactions involving sodium and other dissolved glass constituents increase the pH, and hence the rate of glass dissolution. The precipitation of secondary minerals can also lower the amount of aqueous dissolved silica, which can increase the rate of glass dissolution. Predicted technetium release rates, however, remain several orders of magnitude lower than required by drinking water regulations.