[en] The Waste Isolation Pilot Plant (WIPP) Seal System Performance Program, addresses the sealing of all manmade penetrations. Sealing concepts for shafts, drifts, and boreholes have been developed, and candidate seal materials were identified. Ongoing laboratory tests and model calculations have confirmed the potential effectiveness of reconsolidated WIPP crushed salt as a primary long-term seal material. Grouts based on crushed WIPP salt appear to be viable materials for sealing anhydritic interbeds at drift and panel seal locations. In situ tests have demonstrated the viability of concrete bulkheads as temporary seal materials that preserve the integrity of the seal system until the crushed salt components have reconsolidated sufficiently. Cementitious grouts have also been tested in WIPP boreholes drilled from the surface. Scaled in situ of crushed salt and bentonite (as a temporary seal material to prevent downflow of water into the crushed salt in shafts) are currently underway. Large scale seal tests and the development of models that predict the performance of seal systems are being developed from the test data. 13 refs., 6 figs