WIPP Performance Assessment: A 1990 Snapshot of Compliance With 40 CFR 191, Subpart B

This paper describes the results of the 1990 iteration of the performance assessment for the Waste Isolation Pilot Plant (WIPP) under the Environmental Protection Agency's Standard, Environmental Radiation Standards for Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive Wastes (40 CFR Part 191, Subpart B). This iteration incorporates development and screening of potentially disruptive scenarios. The analysis of the WIPP disposal system's response to the undisturbed scenario and human intrusion scenarios produces preliminary complementary cumulative distribution functions (CCDFs). Similar CCDFs will ultimately be used to evaluate the compliance of the WIPP with the Containment Requirements of the Standard. The conceptual model of the disposal system consists of geologic, hydrologic, and disposal system subsystems along with the physical and chemical processes associated with these subsystems. Parameter values defining the systems contain uncertainties, and modeling approximations of such a disposal system contributes to those uncertainties. The WIPP compliance assessment methodology consists of a system of techniques and computer codes that estimate releases of radionuclides from the disposal system, incorporating analysis of the parameter uncertainties in the estimates. The CCDFs presented are not yet credible enough to judge the final probability of compliance of the WIPP with the EPA Standard. CCDFs for the current WIPP system that are based primarily on conservative reference data, conservative conceptual models, and possible engineered alternatives to the current design will be presented.