Performance assessment of low-level waste disposal facilities using coupled unsaturated flow and reactive transport simulators

摘要

Recent advances in the development of reactive chemical transport simulators have made it possible to use these tools in performance assessments (PAs) for nuclear waste disposal. Reactive transport codes were used to evaluate the impacts of design modifications on the performance of two shallow subsurface disposal systems for low-level radioactive waste. The first disposal system, located at the Hanford site in Richland, Washington, is for disposal of low-level waste glass. Glass waste blocks will be disposed in subsurface trenches, surrounded by backfill material. Using different waste package sizes and layering had a small impact on technetium release rates to the vadose zone. The second disposal system involves a hypothetical repository for low-level waste in Italy. A model of uranium release from a grout waste form was developed using the STORM reactive transport code. Uranium is predicted to be relatively insoluble for several hundred years under the high-pH environment of the cement pore water. The effect of using different filler materials between the waste packages on uranium flux to the vadose zone proved to have a negligible impact on release rates.