Scenario development for the Waste Isolation Pilot Plant Compliance Certification Application

Demonstrating compliance with the applicable regulations for the Waste Isol ation Pilot Plant (WIPP) requires an assessment of the longterm performance of the disposal system. Scenario development is one starting point of this assessment, and generates inquiry about the present state and future evolu tion of the disposal system. Scenario development consists of four tasks: ( i) identifying and classifying features, events and processes (FEPs); (ii) screening FEPs according to well-defined criteria; (iii) forming scenarios (combinations of FEPs) in the context of regulatory performance criteria, a nd (iv) specifying of scenarios for consequence analysis. The development a nd screening of a comprehensive FEP list provides assurance that the identi fication of significant processes and events is complete, that potential in teractions between FEPs are not overlooked, and that responses to possible questions are available and well documented. Two basic scenarios have been identified for the WIPP: undisturbed performance (UP) and disturbed perform ance (DP). The UP scenario is used to evaluate compliance with the Environm ental Protection Agency's (EPA's) Individual Dose (40 CFR 191.15) and Groun dwater Protection (40 CFR 191.24) standards and accounts for all natural an d waste- and repository-induced FEPs that survive the screening process. Th e DP scenario is required fur assessment calculations for the EPA's cumulat ive release standard (Containment Requirements, 40 CFR 191.13) and accounts for disruptive future human events, which have an uncertain probability of occurrence, in addition to the UP FEPs. (C) 2000 Elsevier Science Ltd. All rights reserved.