PNNL

Abstract

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. Two different trench designs were considered, one with four rows of small waste packages, the other with three layers of larger waste packages. One-dimensional simulations were carried out to 20,000 years, whereas two-dimensional simulations could only be carried out for several hundred years due to constraints on computational time. Both the 1-D and 2-D simulations predict that the Technetium release rate from the waste packages will be lower for the new trench design at later times. Because the glass corrosion rate is significantly higher at the backfill/glass interfaces, having less interfacial area in the new trench design offsets the effect of the slightly higher pH relative to the old trench design. In the two-dimensional simulations, water can flow around the waste packages, which causes a decrease in the water flux through the waste packages and lower release rates than predicted in the 1-D simulations. This result reinforces the importance of performing multi-dimensional waste form release simulations.