Characterization of stochastic uncertainty in the 1996 performance assessment for the Waste Isolation Pilot Plant

The 1996 performance assessment (PA) for the Waste Isolation Pilot Plant (WIPP) maintains a separation between stochastic (i.e., aleatory) and subjective (i.e., episternic) uncertainty, with stochastic uncertainty arising from the possible disruptions that could occur at the WIPP over the 10,000 yr regulatory period specified by the U.S. Environmental Protection Agency (40 CFR 191,40 CFR 194) and subjective uncertainty arising from an inability to uniquely characterize many of the inputs required in the 1996 WIPP PA. The characterization of stochastic uncertainty is discussed including drilling intrusion time, drilling locatio~ penetration of excavatedhonexcavated areas of the repository, penetration of pressurized brine beneath the repository, borehole plugging patterns, activity level of waste, and occurrence of potash mining. Additional topics discussed include sampling~rocedures, generation of individual 10,000 yr futures for the WIPP, construction of complementary cumulative distribution functions (CCDFS), mechanistic calculations carried out to support CCDF construction the Kaplan/Garrick ordered &iple representation forrislq and determination of scenarios and scenario probabilities.