Probability, conditional probability and complementary cumulative distribution functions in performance assessment for radioactive waste disposal

A formal description of the structure of several recent performance assessments (PAs) for the Waste Isolation Pilot Plant (WIPP) is given in terms of the following three components: a probability space (Sst, Lst, Pst) for stochastic uncertainty, a probability space (Ssu, Lsu, Psu) for subjective uncertainty and a function (i.e., a random variable) defined on the product space associated with (Sst, Lst, Pst) and (Ssu, Lsu, Psu). The explicit recognition of the existence of these three components allows a careful description of the use of probability, conditional probability and complementary cumulative distribution functions within the WIPP PA. This usage is illustrated in the context of the US Environmental Protection Agencyʹs standard for the geologic disposal of radioactive waste (40 CFR 191, Subpart B). The paradigm described in this presentation can also be used to impose a logically consistent structure on PAs for other complex systems.