Conceptual structure of the 1996 performance assessment for the Waste Isolation Pilot Plant

The conceptual structure of the 1996 performance assessment (PA) for the Waste Isolation Pilot Plant (WIPP) is described. This structure involves three basic entities (EN1, EN2, EN3): (i) EN1, a probabilistic characterization of the likelihood of different futures occurring at the WIPP site over the next 10,000 years; (ii) EN2, a procedure for estimating the radionuclide releases to the accessible environment associated with each of the possible futures that could occur at the WIPP site over the next 10,000 years; and (iii) EN3, a probabilistic characterization of the uncertainty in the parameters used in the definition of EN1 and EN2. In the formal development of the 1996 WIPP PA, EN1 is characterized by a probability space (Sst, Sst, pst) for stochastic (i.e. aleatory) uncertainty; EN2 is characterized by a function f that corresponds to the models and associated computer programs used to estimate radionuclide releases; and EN3 is characterized by a probability space (Ssu, Ssu, psu) for subjective (i.e. epistemic) uncertainty. A high-level overview of the 1996 WIPP PA and references to additional sources of information are given in the context of (Sst, Sst, pst), f and (Ssu, Ssu, psu).