Scenario development for the Waste Isolation Pilot Plant Compliance Certification Application

Demonstrating compliance with the applicable regulations for the Waste Isolation Pilot Plant (WIPP) requires an assessment of the long-term performance of the disposal system. Scenario development is one starting point of this assessment, and generates inquiry about the present state and future evolution 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, and (iv) specifying of scenarios for consequence analysis. The development and screening of a comprehensive FEP list provides assurance that the identification of significant processes and events is complete, that potential interactions 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 performance (DP). The UP scenario is used to evaluate compliance with the Environmental Protection Agencyʹs (EPAʹs) Individual Dose (40 CFR § 191.15) and Groundwater Protection (40 CFR § 191.24) standards and accounts for all natural and waste- and repository-induced FEPs that survive the screening process. The DP scenario is required for assessment calculations for the EPAʹs cumulative 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.