Elements of uncertainty in a radiological performance assessment of a Saltstone Disposal Facility for low level waste

Oak Ridge National Laboratory is currently conducting a radiological performance assessment for the Saltstone Disposal Facility at the Savannah River Site near Aiken, South Carolina. Saltstone is a solidified, low-level waste form which contains very low levels of radionuclides but considerable levels of nitrate. The preliminary results of the performance assessment indicate that the final outcome will be very sensitive to the degradation scenario for the cover and containment system for this facility. The uncertainty in the results beyond several hundred years, arising from the choice of elements in this scenario, is extremely large due to the limited knowledge of the behavior of the clay and cementitious materials beyond this time frame. Design of low-level waste facilities should address this uncertainty, and policy makers and regulators should decide both what the tolerable level of uncertainty is and the length of time over which a facility's performance should be predictively evaluated. 6 refs., 4 figs