Methodology for performance assessment of double-shell tank waste at Hanford

The low-level liquid waste stored in double-shell tanks at Hanford will be solidified in a cementitious matrix (grout) and disposed in subsurface vaults. This paper discusses activities related to the preparation of a site-specific performance assessment as required by DOE Order 5820.2A. A performance assessment is being prepared for the planned grout disposal system at Hanford using site-specific data. The assessment will estimate the incremental increase in the radiological dose to future populations who, after loss of institutional control at the site, use groundwater downgradient of the disposal site. Increases in nonradiological species in water from a hypothetical well will also be estimated. Two-dimensional transport models are being used to estimate contaminant concentrations in groundwater. Sensitivity studies on various parameters are in progress. This performance assessment will be updated as additional data become available. 16 refs., 1 fig., 2 tabs.