Conceptual basis of a systems prioritization methodology for the Waste Isolation Pilot Plant

A systems prioritization methodology (SPM) is under development at Sandia National Laboratories (SNL) to provide guidance to the US Department of Energy (DOE) on experimental programs and design modifications to be supported in the development of a successful compliance certification application to the US Environmental Protection Agency (EPA) for the Waste Isolation Pilot Plant (WIPP) for the geologic disposal of transuranic (TRU) waste. The purpose of the SPM is to determine the probabilities that the implementation of different combinations of experimental programs and design modifications, referred to as activity sets, will lead to compliance with 40 CFR 191, Subparts B and C (Environmental Radiation Protection Standards for the Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Waste) and 40 CFR 268·6 (Petitions to Allow Land Disposal of a Waste Prohibited under Subpart C of Part 268, which implements the Resource Conservation and Recovery Act, i.e., RCRA). Appropriate tradeoffs between compliance probability, implementation cost and implementation time can then be made in the selection of the activity set to be supported in the development of a licensing application. Determination of compliance probabilities for individual activity sets involves probability spaces for (1) possible outcomes of the experimental programs, (2) uncertainty in analysis input given specific experimental outcomes and (3) possible future occurrences at the WIPP, and also models for (1) fluid flow in the vicinity of the repository, (2) radionuclide release from the repository due to flowing groundwater, (3) groundwater flow and radionuclide transport in geologic formations overlying the repository, (4) radionuclide release to the surface environment due to cuttings and spallings removal in the event of a drilling intrusion and (5) transport of RCRA contaminants in gas and brine. Descriptions are given for the conceptual structure of the SPM and the manner in which this structure determines the computational implementation of an example SPM application. Due to the sophisticated structure of the SPM and the computational demands of many of its components, the overall computational structure must be organized carefully to provide the compliance probabilities for the large number of activity sets under consideration at an acceptable computational cost. Conceptually, the determination of each compliance probability is equivalent to a large numerical integration problem.