Overview of Performance Assessment for the Waste Isolation Pilot Plant

The Waste Isolation Pilot Plant (WIPP) has been developed by the U.S. Department of Energy for the geologic (deep underground) disposal of transuranic waste. Compliance with the containment requirements is demonstrated by means of performance assessment (PA). The term PA signifies an analysis that 1) identifies the features, processes and events (FEPs) that might affect the disposal system; 2) examines the effects of these FEPs on the performance of the disposal system; 3) estimates the cumulative releases of radionuclides caused by all significant FEPs; and 4) accounts for uncertainty in the parameters of the PA models. Modifying the WIPP PA is a reoccurring process, which ensures confidence in the PA results. The updated WIPP PA demonstrates that the results continue to lie entirely below the specified limits and the WIPP therefore continues to be in compliance with the containment requirements. Analysis of the results shows that the total releases are dominated by radionuclide releases that could occur during an inadvertent penetration of the repository by a future drilling operation. The natural and engineered barrier systems of the WIPP provide robust and effective containment of transuranic waste even if the repository is penetrated by multiple borehole intrusions.