Subsidence Study for Non-Crushable Containers in Slit Trenches at the Savannah River Site

摘要

Using PC-based PorFlow™ Version 5.97, this study addresses the issue of waste and cover subsidence caused by corrosion of the non-crushable waste containers defined as containers with significant void space that will not be stabilized by dynamic compaction of the E-area Slit Trenches at the Savanaah River Site (SRS). Concentrations at the hypothetical 100-m (distance) well were evaluated for 1,000 years and compared with the base case value for compliance. To generalize the results, a hypothetical, no-decay radionuclide characterized by a partition coefficient Kd (5 ml/g) that would be most problematic was selected. Although the non-crushable containers will not be stabilized by dynamic compaction, these containers will gradually corrode, eventually collapse after placement of the final closure cap and cause the cap to subside resulting in an increase of the infiltration rates. The vadose zone model estimated the contaminant fluxes that were input to the aquifer model for prediction of concentrations at the 100-m well.rnTo study the potential effect of trench subsidence on the well concentrations (i.e., concentrations at the 100-m well) within the 1000-year time window, two high-impact cases were considered. In the first case, trenches subsided right after dynamic compaction (i.e., at 125 years). In the second case, trenches subsided at 419 years to make the peak concentrations from both the subsided and unsubsided area align in space and time. The study shows that the first case presented no compliance problem for the subsidence of up to two trenches. In the second case, even a single trench subsidence caused the well concentration to be out of compliance. The peak concentration exceeded the base case value by as much as 15%. This paper discusses the general modeling approach and presents the study results.